Chapter: Respiratory System Anatomy; Topic: Larynx; Subtopic: Cartilages of Larynx
Keyword Definitions:
Larynx: A cartilaginous structure located in the neck that houses the vocal cords and is involved in breathing, sound production, and airway protection.
Unpaired cartilage: Cartilages that occur singly in the larynx such as thyroid, cricoid, and epiglottis.
Paired cartilage: Cartilages that occur in pairs, including arytenoid, corniculate, and cuneiform.
Epiglottis: A leaf-shaped unpaired cartilage that covers the glottis during swallowing, preventing aspiration.
Arytenoid cartilage: Paired cartilages involved in vocal cord movement and phonation.
Lead Question – 2014
Unpaired laryngeal cartilage ?
a) Arytenoid
b) Corniculate
c) Cuneiform
d) Epiglottis
Explanation:
The larynx consists of three unpaired (thyroid, cricoid, epiglottis) and three paired cartilages (arytenoid, corniculate, cuneiform). The epiglottis is a leaf-shaped unpaired cartilage that prevents food from entering the trachea during swallowing. It plays a crucial role in protecting the airway and facilitating speech. Hence, the correct answer is epiglottis (d).
1) Which cartilage forms a complete ring in the larynx?
a) Thyroid
b) Cricoid
c) Arytenoid
d) Corniculate
Explanation: The cricoid cartilage forms a complete ring around the larynx and is the only cartilage with such structure. It provides structural support and connects the larynx to the trachea. The correct answer is cricoid (b).
2) The vocal cords are attached posteriorly to which cartilage?
a) Thyroid
b) Cricoid
c) Arytenoid
d) Epiglottis
Explanation: The vocal cords are attached posteriorly to the arytenoid cartilages and anteriorly to the thyroid cartilage. Arytenoids control tension and position of vocal cords for phonation. The correct answer is arytenoid (c).
3) Which nerve supplies the cricothyroid muscle?
a) Recurrent laryngeal nerve
b) External branch of superior laryngeal nerve
c) Glossopharyngeal nerve
d) Internal laryngeal nerve
Explanation: The cricothyroid muscle is supplied by the external branch of the superior laryngeal nerve. It tenses the vocal cords and modulates pitch. The correct answer is external branch of superior laryngeal nerve (b).
4) A patient with hoarseness after thyroid surgery has likely injured which nerve?
a) Recurrent laryngeal
b) Phrenic
c) Glossopharyngeal
d) Accessory
Explanation: The recurrent laryngeal nerve innervates most intrinsic laryngeal muscles responsible for voice production. Injury during thyroid surgery leads to hoarseness or voice loss. The correct answer is recurrent laryngeal nerve (a).
5) Which muscle abducts the vocal cords?
a) Lateral cricoarytenoid
b) Posterior cricoarytenoid
c) Thyroarytenoid
d) Cricothyroid
Explanation: The posterior cricoarytenoid is the only abductor of the vocal cords, opening the rima glottidis during inspiration. Paralysis causes airway obstruction. The correct answer is posterior cricoarytenoid (b).
6) A child presents with high-pitched breathing after choking. The likely site of obstruction is?
a) Trachea
b) Larynx
c) Nasopharynx
d) Bronchi
Explanation: Stridor, a high-pitched sound, indicates laryngeal obstruction. The larynx’s narrow lumen in children predisposes them to airway compromise. The correct answer is larynx (b).
7) Which cartilage provides attachment for the vocal cords anteriorly?
a) Thyroid
b) Cricoid
c) Arytenoid
d) Epiglottis
Explanation: The anterior ends of the vocal cords attach to the thyroid cartilage at the laryngeal prominence. It provides anchoring for sound modulation. The correct answer is thyroid (a).
8) The laryngeal inlet is guarded by which structure during swallowing?
a) Epiglottis
b) Aryepiglottic fold
c) Vocal cords
d) Cricoid cartilage
Explanation: During swallowing, the epiglottis folds down to cover the laryngeal inlet, preventing food from entering the trachea. The correct answer is epiglottis (a).
9) Which of the following is a paired laryngeal cartilage?
a) Epiglottis
b) Thyroid
c) Corniculate
d) Cricoid
Explanation: The corniculate cartilages are small paired nodules situated on the apices of arytenoid cartilages, assisting in voice production and airway control. The correct answer is corniculate (c).
10) During intubation, which cartilage is felt as the "Adam’s apple"?
a) Cricoid
b) Thyroid
c) Epiglottis
d) Arytenoid
Explanation: The thyroid cartilage projects anteriorly to form the Adam’s apple, most prominent in males. It protects the vocal cords and serves as an important landmark for cricothyrotomy. The correct answer is thyroid (b).
Subtopic: Bronchopulmonary Segments
Keyword Definitions:
Bronchopulmonary segment: A distinct, functionally independent unit of a lung, supplied by its own bronchus and artery.
Lobes of lung: The right lung has three lobes, while the left has two lobes due to the position of the heart.
Segmental bronchus: The tertiary bronchus supplying each bronchopulmonary segment.
Pulmonary circulation: The blood flow between the heart and lungs for oxygenation.
Lead Question (2014):
Bronchopulmonary segments in right and left lungs respectively?
a) 9, 11
b) 11, 9
c) 10, 10
d) 8, 10
Explanation:
Each lung is divided into bronchopulmonary segments — 10 on the right and 8–10 on the left. These segments are separated by connective tissue and have independent blood supply and airways. Answer: c) 10, 10. This structural independence allows surgical removal of one segment without affecting others.
1)
Which bronchopulmonary segment of the right lung is most prone to aspiration of foreign bodies in a supine patient?
a) Apical
b) Posterior
c) Superior segment of lower lobe
d) Medial basal
In supine position, aspirated material often enters the superior segment of the right lower lobe due to the bronchus’ vertical orientation. Answer: c) Superior segment of lower lobe. This segment’s airway is a direct continuation of the bronchus, making it the commonest aspiration site.
2)
Which of the following statements about bronchopulmonary segments is true?
a) Veins lie within the segments
b) Arteries are intersegmental
c) Veins are intersegmental
d) Each segment shares arteries
Pulmonary veins are intersegmental, draining blood between segments, while arteries and bronchi are segmental. Answer: c) Veins are intersegmental. This distinct arrangement facilitates anatomical lung resections with minimal bleeding and segmental preservation during surgery.
3)
A 40-year-old man undergoes segmentectomy for localized bronchiectasis. Which feature helps the surgeon identify the diseased segment?
a) Segmental artery
b) Lymphatic drainage
c) Intersegmental veins
d) Bronchioles pattern
During surgery, intersegmental veins mark the boundaries between bronchopulmonary segments. Answer: c) Intersegmental veins. These veins run in connective tissue planes separating adjacent segments and act as important anatomical landmarks in lung segmental resections.
4)
How many bronchopulmonary segments are present in the left lung?
a) 9
b) 10
c) 8–10
d) 11
The left lung has 8–10 segments, commonly described as 8 due to fusion of some segments. Answer: c) 8–10. The left upper lobe segments are often fused, such as apicoposterior, leading to minor variations in segment counts among individuals.
5)
A patient with tuberculosis develops localized cavitation in the apical segment of the upper lobe. This infection affects which lung region?
a) Apex of right lower lobe
b) Apical segment of right upper lobe
c) Superior segment of middle lobe
d) Anterior basal segment
Tuberculosis commonly involves the apical segment of the upper lobe due to higher oxygen tension supporting bacterial growth. Answer: b) Apical segment of right upper lobe. This region has better aeration and is less perfused, creating a favorable environment for Mycobacterium tuberculosis.
6)
Each bronchopulmonary segment is supplied by which of the following?
a) Primary bronchus
b) Secondary bronchus
c) Tertiary bronchus
d) Terminal bronchiole
Each bronchopulmonary segment receives air through a tertiary or segmental bronchus, along with its own artery. Answer: c) Tertiary bronchus. This independent supply allows selective surgical removal of diseased segments without compromising adjacent lung areas or causing collapse.
7)
A 50-year-old chronic smoker presents with localized carcinoma confined to one bronchopulmonary segment. What type of surgical procedure is most suitable?
a) Lobectomy
b) Segmentectomy
c) Pneumonectomy
d) Wedge resection
Segmentectomy is removal of a bronchopulmonary segment while preserving the rest of the lobe. Answer: b) Segmentectomy. It is preferred when the lesion is confined to a single segment, ensuring preservation of maximal healthy lung tissue for respiratory function.
8)
Which structure separates bronchopulmonary segments from one another?
a) Elastic tissue
b) Connective tissue septa
c) Bronchial cartilage
d) Pleural folds
Each bronchopulmonary segment is separated by thin connective tissue septa containing intersegmental veins. Answer: b) Connective tissue septa. This separation permits selective surgical resection and defines the anatomic boundaries between individual functional lung units.
9)
A CT scan reveals consolidation limited to the medial basal segment of the right lower lobe. Which bronchus is affected?
a) Tertiary bronchus of right middle lobe
b) Medial basal segmental bronchus
c) Superior segmental bronchus
d) Posterior basal bronchus
Each segment has its own bronchus, and infection in the medial basal segment implies involvement of the medial basal segmental bronchus. Answer: b) Medial basal segmental bronchus. Such localized findings help radiologists identify exact sites of pulmonary infection or tumor growth.
10)
Which of the following statements about surgical importance of bronchopulmonary segments is correct?
a) They cannot be removed independently
b) Each segment has its own venous drainage
c) Segments are not functionally separate
d) They share bronchi among lobes
Each segment is functionally independent, supplied by its own bronchus and artery, allowing isolated removal. Answer: b) Each segment has its own venous drainage. This independence makes bronchopulmonary segmentation crucial in surgical planning and pulmonary disease localization.
Topic: Lungs and Bronchi
Subtopic: Right Principal Bronchus
Keyword Definitions:
Principal bronchus: Primary bronchus arising from trachea, supplying each lung.
Right principal bronchus: Wider, shorter, and more vertical than left; directs aspirated foreign bodies.
Left principal bronchus: Longer, narrower, and more horizontal, passing under arch of aorta.
Trachea: Airway tube dividing at carina into right and left bronchi.
Lobar bronchus: Secondary bronchus supplying each lobe of the lung.
Lead Question - 2014
True about right principal bronchus ?
a) Narrower
b) Horizontal
c) Shorter
d) All are true
Explanation: The right principal bronchus is wider, shorter, and more vertical compared to left. This explains why inhaled foreign bodies often lodge in right lung. It is not narrower or horizontal. Correct answer is c) Shorter. Knowledge of bronchial anatomy is crucial for bronchoscopy and foreign body removal. (50 words)
1. Which bronchus is more prone to foreign body aspiration?
a) Right
b) Left
c) Both equally
d) Neither
Explanation: Right principal bronchus is wider, shorter, and vertical, creating a direct path for foreign bodies. Left is narrower and oblique. Correct answer is a) Right. This anatomical difference explains clinical findings in children and adults with accidental aspiration. Prompt bronchoscopy is needed for removal. (50 words)
2. Left principal bronchus passes beneath which structure?
a) Arch of aorta
b) Superior vena cava
c) Right pulmonary artery
d) Right atrium
Explanation: The left bronchus is longer and runs beneath the arch of aorta and anterior to esophagus. Correct answer is a) Arch of aorta. Its oblique path protects it from direct entry of foreign bodies. Important in imaging and thoracic surgeries involving mediastinum. (50 words)
3. Carina corresponds to which vertebral level?
a) T2
b) T4
c) T6
d) T8
Explanation: Carina, the ridge where trachea bifurcates into principal bronchi, lies at the level of T4/T5 intervertebral disc and sternal angle. Correct answer is b) T4. The carina is a sensitive structure; irritation triggers cough reflex, important in bronchoscopy. (50 words)
4. During bronchoscopy, foreign body is seen lodged in right middle lobe bronchus. This is branch of:
a) Left bronchus
b) Right principal bronchus
c) Trachea directly
d) Posterior mediastinum
Explanation: Right principal bronchus divides into three lobar bronchi—upper, middle, and lower—supplying corresponding lobes. A foreign body in right middle lobe bronchus originates from right principal bronchus. Correct answer is b) Right principal bronchus. Knowledge of lobar divisions is crucial for targeted bronchoscopy and segmentectomy. (50 words)
5. Which artery crosses anterior to right principal bronchus?
a) Right pulmonary artery
b) Left pulmonary artery
c) Ascending aorta
d) Subclavian artery
Explanation: The right pulmonary artery crosses anterior to the right principal bronchus. On the left, pulmonary artery passes superior to left bronchus. Correct answer is a) Right pulmonary artery. These relationships are important during pulmonary angiography, mediastinal surgery, and CT interpretation. (50 words)
6. Which bronchus is longer and narrower?
a) Right
b) Left
c) Both equal
d) Neither
Explanation: Left principal bronchus is longer (5 cm) and narrower, with a more oblique course compared to right. Correct answer is b) Left. This makes aspiration less common on the left side. Anatomical difference is important in intubation and pathology interpretation. (50 words)
7. A 3-year-old child aspirates a peanut. It is most likely found in:
a) Left upper lobe bronchus
b) Right lower lobe bronchus
c) Left lower lobe bronchus
d) Trachea
Explanation: Due to vertical orientation, right lower lobe bronchus is the most common site for foreign body aspiration. Correct answer is b) Right lower lobe bronchus. Radiological confirmation and prompt bronchoscopy are essential for removal. This is a frequent pediatric emergency. (50 words)
8. The angle between right principal bronchus and trachea is:
a) 25°
b) 45°
c) 60°
d) 90°
Explanation: Right principal bronchus forms an angle of about 25° with trachea, making it more in line with tracheal axis. Left forms an angle of about 45°. Correct answer is a) 25°. This anatomical angle explains clinical predisposition for right-sided aspiration. (50 words)
9. Which structure lies posterior to left principal bronchus?
a) Azygos vein
b) Descending thoracic aorta
c) Superior vena cava
d) Right atrium
Explanation: The descending thoracic aorta lies posterior to the left principal bronchus. Correct answer is b) Descending thoracic aorta. This anatomical relation is significant in mediastinal imaging and during surgeries involving aortic aneurysms. (50 words)
10. In case of bronchogenic carcinoma of right main bronchus, which symptom is most expected?
a) Hoarseness
b) Cough with aspiration
c) Hematuria
d) Dysphagia
Explanation: Tumors involving right principal bronchus commonly present with cough and recurrent aspiration pneumonia due to obstruction. Correct answer is b) Cough with aspiration. Other symptoms may include wheezing, hemoptysis, and dyspnea. Clinical correlation with imaging and bronchoscopy is essential for diagnosis. (50 words)
Chapter: Respiratory Physiology
Topic: Pulmonary Circulation
Subtopic: Hypoxic Pulmonary Vasoconstriction (HPV)
Keywords:
Hypoxic Pulmonary Vasoconstriction (HPV): Physiological mechanism where pulmonary arteries constrict in low oxygen regions to divert blood to better-ventilated alveoli, optimizing gas exchange.
Reversible Vasoconstriction: Vasoconstriction that resolves when oxygen levels normalize, allowing dynamic regulation of pulmonary blood flow.
Irreversible Vasoconstriction: Permanent narrowing of pulmonary vessels due to chronic hypoxia, contributing to pulmonary hypertension.
Ventilation-Perfusion (V/Q) Matching: Process by which blood flow is matched to areas of the lung with higher ventilation for optimal gas exchange.
Lead Question - 2013:
Hypoxic pulmonary vasoconstriction due to -
a) Irreversible pulmonary vasocontriction hypoxia
b) Reversible pulmonary vasoconstriction due to hypoxia
c) Direct blood to poorly ventilated areas
d) Occurs hours after pulmonary vasoconstriction
Answer & Explanation:
Correct answer: b) Reversible pulmonary vasoconstriction due to hypoxia.
Explanation: Hypoxic pulmonary vasoconstriction (HPV) is a protective, reversible mechanism. It reduces blood flow to poorly ventilated areas of the lung, improving V/Q matching. The process is reversible and occurs within seconds of hypoxia, optimizing oxygenation. Chronic hypoxia may lead to irreversible changes but is not the primary mechanism.
MCQ 1:
What is the primary purpose of hypoxic pulmonary vasoconstriction?
a) Increase systemic blood pressure
b) Prevent alveolar collapse
c) Optimize V/Q matching
d) Reduce cardiac output
Answer & Explanation:
Correct answer: c) Optimize V/Q matching.
Explanation: HPV serves to match ventilation to perfusion by diverting blood from poorly ventilated alveoli to well-ventilated ones. This adaptive mechanism improves gas exchange efficiency by maintaining optimal oxygen and CO₂ balance in the blood, especially during localized hypoxia or lung disease.
MCQ 2 (Clinical):
Which clinical condition commonly leads to exaggerated hypoxic pulmonary vasoconstriction?
a) Asthma
b) Chronic obstructive pulmonary disease (COPD)
c) Pneumonia
d) Pulmonary embolism
Answer & Explanation:
Correct answer: b) Chronic obstructive pulmonary disease (COPD).
Explanation: In COPD, chronic alveolar hypoxia leads to persistent HPV, contributing to pulmonary hypertension. The repeated or sustained hypoxic stimulus causes thickening of pulmonary arterial walls and vascular remodeling, increasing pulmonary vascular resistance and leading to right heart strain over time.
MCQ 3:
Hypoxic pulmonary vasoconstriction occurs predominantly in response to:
a) Systemic hypoxia
b) Local alveolar hypoxia
c) High PaCO₂
d) Hypercapnia
Answer & Explanation:
Correct answer: b) Local alveolar hypoxia.
Explanation: HPV is triggered by localized alveolar hypoxia, not systemic hypoxia. It enables redistribution of blood flow from poorly ventilated alveoli to better-ventilated areas, enhancing overall gas exchange. Systemic hypoxia affects peripheral chemoreceptors but does not directly cause HPV.
MCQ 4 (Clinical):
A patient with interstitial lung disease shows persistent pulmonary hypertension. The likely mechanism is:
a) Excessive oxygen therapy
b) Chronic hypoxia-induced HPV
c) Increased left atrial pressure
d) Systemic hypotension
Answer & Explanation:
Correct answer: b) Chronic hypoxia-induced HPV.
Explanation: In interstitial lung disease, sustained alveolar hypoxia triggers chronic HPV, leading to pulmonary arterial remodeling and hypertension. Over time, irreversible structural changes in the pulmonary vasculature develop, worsening pulmonary hypertension and right heart dysfunction.
MCQ 5:
Which of the following statements is TRUE about HPV?
a) Occurs minutes after hypoxia
b) Irreversible
c) Reversible and rapid
d) Causes increased alveolar oxygenation
Answer & Explanation:
Correct answer: c) Reversible and rapid.
Explanation: HPV occurs rapidly, within seconds to minutes of alveolar hypoxia, and is reversible upon reoxygenation. This ensures a quick adaptive response to regional ventilation deficits, improving ventilation-perfusion matching without causing systemic effects, unless sustained hypoxia leads to irreversible vascular changes.
MCQ 6 (Clinical):
Which drug is known to inhibit hypoxic pulmonary vasoconstriction?
a) Albuterol
b) Nitric oxide
c) Furosemide
d) Beta-blockers
Answer & Explanation:
Correct answer: b) Nitric oxide.
Explanation: Inhaled nitric oxide selectively dilates pulmonary vessels and inhibits HPV. Clinically, it is used in cases of persistent pulmonary hypertension of the newborn (PPHN) or acute respiratory distress syndrome (ARDS) to improve oxygenation without systemic hypotension.
MCQ 7:
Which is a potential negative consequence of global hypoxic pulmonary vasoconstriction?
a) Improved oxygenation
b) Pulmonary hypertension
c) Enhanced ventilation
d) Reduced cardiac workload
Answer & Explanation:
Correct answer: b) Pulmonary hypertension.
Explanation: While localized HPV is adaptive, global hypoxia leads to widespread pulmonary vasoconstriction, increasing pulmonary vascular resistance. This chronic effect can cause pulmonary hypertension and strain the right ventricle, potentially leading to right heart failure in long-term conditions like COPD or sleep apnea.
MCQ 8:
Which cells primarily mediate HPV?
a) Type I alveolar cells
b) Endothelial cells
c) Smooth muscle cells of pulmonary arteries
d) Alveolar macrophages
Answer & Explanation:
Correct answer: c) Smooth muscle cells of pulmonary arteries.
Explanation: HPV is mediated by contraction of smooth muscle cells in small pulmonary arteries and arterioles. Low alveolar oxygen tension causes these muscle cells to constrict, redirecting blood flow, which enhances gas exchange efficiency during localized hypoxia.
MCQ 9 (Clinical):
A patient with high-altitude exposure develops increased pulmonary arterial pressure. This is due to:
a) Dehydration
b) Systemic vasoconstriction
c) Hypoxic pulmonary vasoconstriction
d) Hyperventilation
Answer & Explanation:
Correct answer: c) Hypoxic pulmonary vasoconstriction.
Explanation: At high altitude, reduced atmospheric oxygen leads to generalized alveolar hypoxia, causing global HPV. The resulting increased pulmonary vascular resistance elevates pulmonary arterial pressure, contributing to high-altitude pulmonary hypertension and risk of edema without effective acclimatization.
MCQ 10:
Which factor does NOT influence hypoxic pulmonary vasoconstriction?
a) Alveolar oxygen tension
b) Systemic arterial CO₂
c) pH of CSF
d) Sympathetic nervous system activity
Answer & Explanation:
Correct answer: c) pH of CSF.
Explanation: Central chemoreceptors respond to CSF pH, not directly influencing HPV. HPV is primarily driven by alveolar oxygen tension. Sympathetic nervous system may modulate pulmonary vascular tone, and systemic arterial CO₂ indirectly affects ventilation, but pH of CSF is not a direct mediator of HPV.
Chapter: Respiratory Physiology
Topic: Control of Respiration
Subtopic: Chemoreceptor Function
Keywords:
Central Chemoreceptors: Located in the medulla oblongata, sensitive to changes in CO₂ and pH in cerebrospinal fluid, regulating ventilation.
PaCO₂ (Partial Pressure of CO₂): The pressure exerted by CO₂ in arterial blood, a major factor influencing central chemoreceptor activity.
pH: A measure of hydrogen ion concentration; affects chemoreceptor response, especially in central regulation of respiration.
TP O₂ (Total Partial Pressure of O₂): Partial pressure of oxygen in arterial blood, primarily sensed by peripheral chemoreceptors.
Lead Question - 2013:
Central Chemoreceptors are most sensitive to following changes in blood:
a) TPCO₂
b) I PCO₂
c) TH+
d) T PO₂
Answer & Explanation:
Correct answer: a) TPCO₂.
Explanation: Central chemoreceptors are most sensitive to changes in total partial pressure of CO₂ (TPCO₂) in the blood. Elevated CO₂ crosses the blood-brain barrier, increasing H⁺ concentration in cerebrospinal fluid and stimulating chemoreceptors to increase ventilation. Oxygen levels (T PO₂) are sensed by peripheral chemoreceptors.
MCQ 1:
Where are central chemoreceptors located?
a) Carotid body
b) Aortic arch
c) Medulla oblongata
d) Hypothalamus
Answer & Explanation:
Correct answer: c) Medulla oblongata.
Explanation: Central chemoreceptors are situated in the medulla oblongata near the respiratory centers. They respond primarily to elevated CO₂ by sensing changes in cerebrospinal fluid pH, thus regulating ventilation rate and depth to maintain homeostasis of blood gases.
MCQ 2 (Clinical):
In which condition is central chemoreceptor sensitivity reduced?
a) Chronic hypercapnia
b) Acute hypoxia
c) Pulmonary embolism
d) Asthma
Answer & Explanation:
Correct answer: a) Chronic hypercapnia.
Explanation: In chronic hypercapnia, as seen in COPD, central chemoreceptors adapt by becoming less sensitive to CO₂, relying more on peripheral chemoreceptors (which respond to low O₂) for respiratory drive. This is a critical consideration in managing chronic respiratory patients clinically.
MCQ 3:
Peripheral chemoreceptors primarily respond to changes in:
a) CO₂
b) pH
c) O₂
d) Temperature
Answer & Explanation:
Correct answer: c) O₂.
Explanation: Peripheral chemoreceptors in the carotid and aortic bodies primarily respond to low oxygen levels (hypoxemia), as well as pH and CO₂ changes to a lesser extent. Central chemoreceptors do not directly sense O₂ but respond to CO₂ and H⁺ levels in cerebrospinal fluid.
MCQ 4 (Clinical):
Which condition stimulates central chemoreceptors leading to hyperventilation?
a) Hypocapnia
b) Hypercapnia
c) Anemia
d) Polycythemia
Answer & Explanation:
Correct answer: b) Hypercapnia.
Explanation: Elevated arterial CO₂ (hypercapnia) crosses the blood-brain barrier, increasing cerebrospinal fluid H⁺ concentration. Central chemoreceptors sense this acidification, triggering increased respiratory rate and depth (hyperventilation) to expel CO₂ and restore homeostasis in conditions like respiratory failure.
MCQ 5:
Which is NOT true about central chemoreceptors?
a) They respond to changes in PaCO₂
b) They directly sense arterial pH
c) Located in medulla oblongata
d) Influence ventilation rate
Answer & Explanation:
Correct answer: b) They directly sense arterial pH.
Explanation: Central chemoreceptors do not directly respond to arterial pH but detect pH changes in cerebrospinal fluid due to CO₂ diffusion. Arterial H⁺ cannot cross the blood-brain barrier, so central chemoreceptors specifically respond to CO₂ levels impacting CSF pH.
MCQ 6 (Clinical):
Why is oxygen not a major stimulus for central chemoreceptors?
a) O₂ readily crosses blood-brain barrier
b) O₂ does not affect CSF pH
c) O₂ directly stimulates respiratory centers
d) O₂ sensitivity is higher than CO₂
Answer & Explanation:
Correct answer: b) O₂ does not affect CSF pH.
Explanation: Central chemoreceptors detect changes in CSF pH primarily caused by CO₂ diffusion. Oxygen does not significantly alter CSF pH, and its partial pressure is sensed by peripheral chemoreceptors. Therefore, central chemoreceptors mainly regulate ventilation by responding to CO₂ levels.
MCQ 7:
Which chemical change triggers central chemoreceptor response?
a) Increased H+ concentration
b) Decreased PaO₂
c) Decreased HCO₃⁻
d) Increased blood glucose
Answer & Explanation:
Correct answer: a) Increased H+ concentration.
Explanation: Central chemoreceptors are activated by increased H⁺ concentration in the cerebrospinal fluid, which occurs when arterial CO₂ rises and crosses into the CSF, producing carbonic acid and increasing acidity, thereby stimulating respiratory centers to enhance ventilation.
MCQ 8 (Clinical):
A patient with brain injury has suppressed central chemoreceptor function. What is expected?
a) Increased ventilation
b) Decreased respiratory drive
c) Hyperventilation
d) Tachypnea
Answer & Explanation:
Correct answer: b) Decreased respiratory drive.
Explanation: Damage to the medulla impairs central chemoreceptor function, blunting the ventilatory response to CO₂ accumulation. This leads to decreased respiratory drive, risk of CO₂ retention, and respiratory acidosis, necessitating mechanical ventilation and close clinical monitoring.
MCQ 9:
Which ion change directly stimulates central chemoreceptors?
a) Increase in Na⁺
b) Decrease in K⁺
c) Increase in H⁺
d) Decrease in Cl⁻
Answer & Explanation:
Correct answer: c) Increase in H⁺.
Explanation: Central chemoreceptors respond to increased H⁺ concentration in the CSF, which reflects elevated PaCO₂ levels. This stimulates the respiratory centers in the medulla to increase ventilation, aiming to reduce CO₂ and restore acid-base balance.
MCQ 10 (Clinical):
Which situation would least stimulate central chemoreceptors?
a) Hypoventilation
b) Hypercapnia
c) Hypoxia
d) Increased PaCO₂
Answer & Explanation:
Correct answer: c) Hypoxia.
Explanation: Central chemoreceptors are insensitive to hypoxia; they predominantly respond to CO₂ and pH changes in the CSF. Hypoxia stimulates peripheral chemoreceptors in the carotid and aortic bodies, making oxygen a poor direct stimulus for central chemoreceptors during respiratory control.
Chapter: Respiratory Physiology
Topic: Pulmonary Function Tests
Subtopic: Dead Space Measurement
Keywords:
Physiological Dead Space: The total volume of the lungs that does not participate in gas exchange, including anatomical and alveolar dead space.
Bohr Equation: A formula used to calculate the physiological dead space based on CO₂ concentration differences between alveolar gas and expired air.
Dalton’s Law: States that the total pressure exerted by a mixture of non-reacting gases is equal to the sum of the partial pressures of individual gases.
Boyle's Law: Describes the inverse relationship between pressure and volume of gas at constant temperature (PV = constant).
Lead Question - 2013:
Physiological dead space is calculated by ?
a) Boyle's law
b) Dalton's law
c) Bohr equation
d) Charle's law
Answer & Explanation:
Correct answer: c) Bohr equation.
Explanation: Physiological dead space is calculated using the Bohr equation, which evaluates the fraction of tidal volume that does not participate in gas exchange by comparing CO₂ concentrations in alveolar and expired air. This calculation is crucial in assessing ventilation efficiency, especially in pulmonary diseases.
MCQ 1:
What does the Bohr equation primarily measure?
a) Lung compliance
b) Physiological dead space
c) Airway resistance
d) Tidal volume
Answer & Explanation:
Correct answer: b) Physiological dead space.
Explanation: The Bohr equation calculates physiological dead space, representing the portion of inspired air not engaged in gas exchange. It compares alveolar and expired CO₂ concentrations, serving as an important index in evaluating respiratory disorders and mechanical ventilation efficiency.
MCQ 2 (Clinical):
In which condition is physiological dead space expected to be significantly increased?
a) Pulmonary embolism
b) Asthma
c) Bronchitis
d) Normal lungs
Answer & Explanation:
Correct answer: a) Pulmonary embolism.
Explanation: Pulmonary embolism blocks pulmonary blood flow, resulting in alveoli that are ventilated but not perfused. This increases physiological dead space and impairs gas exchange efficiency, leading to hypoxemia and requiring urgent diagnosis and treatment in clinical practice.
MCQ 3:
Which is NOT a component of physiological dead space?
a) Anatomical dead space
b) Alveolar dead space
c) Residual volume
d) Both anatomical and alveolar dead space
Answer & Explanation:
Correct answer: c) Residual volume.
Explanation: Physiological dead space consists of anatomical dead space (airways not participating in gas exchange) and alveolar dead space (non-perfused alveoli). Residual volume is the air remaining in the lungs after maximal expiration and is not part of dead space calculation.
MCQ 4 (Clinical):
Why is measuring physiological dead space clinically useful?
a) To assess lung compliance
b) To detect airway obstruction
c) To evaluate gas exchange inefficiency
d) To measure blood oxygen content
Answer & Explanation:
Correct answer: c) To evaluate gas exchange inefficiency.
Explanation: Measuring physiological dead space helps assess the efficiency of ventilation and gas exchange. Elevated dead space suggests ventilation-perfusion mismatch, which can be caused by diseases like pulmonary embolism, chronic obstructive pulmonary disease, or acute respiratory distress syndrome.
MCQ 5:
Which law is used to describe the relationship between gas pressure and volume?
a) Bohr equation
b) Dalton’s law
c) Boyle’s law
d) Charles’s law
Answer & Explanation:
Correct answer: c) Boyle’s law.
Explanation: Boyle's Law states that pressure and volume of a gas are inversely proportional at constant temperature. This principle explains lung inflation and deflation during breathing but is not used to calculate physiological dead space.
MCQ 6 (Clinical):
How does COPD affect physiological dead space?
a) Decreases it
b) No change
c) Increases it
d) Eliminates it
Answer & Explanation:
Correct answer: c) Increases it.
Explanation: COPD leads to destruction of alveolar walls and poor perfusion, causing more alveoli to be ventilated but not perfused, increasing physiological dead space. This worsens gas exchange and contributes to hypoxia, making dead space measurement crucial in clinical assessments.
MCQ 7:
Dalton’s law pertains to?
a) Volume and pressure
b) Gas solubility
c) Partial pressures of gases in a mixture
d) Gas temperature relationship
Answer & Explanation:
Correct answer: c) Partial pressures of gases in a mixture.
Explanation: Dalton’s Law states that the total pressure of a gas mixture equals the sum of the partial pressures of individual gases. This principle is important in understanding gas exchange but does not calculate physiological dead space.
MCQ 8 (Clinical):
Which clinical tool helps measure expired CO₂ for Bohr equation calculation?
a) Spirometer
b) Capnograph
c) Pulse oximeter
d) Peak flow meter
Answer & Explanation:
Correct answer: b) Capnograph.
Explanation: A capnograph continuously measures the CO₂ concentration in exhaled air, allowing clinicians to calculate physiological dead space using the Bohr equation. It provides important data about ventilation and perfusion status, especially during anesthesia and in critically ill patients.
MCQ 9:
Physiological dead space fraction (VD/VT) in healthy adults is approximately?
a) 0.1
b) 0.3
c) 0.5
d) 0.7
Answer & Explanation:
Correct answer: b) 0.3.
Explanation: In healthy adults, the physiological dead space fraction (VD/VT) is typically around 0.3, meaning about 30% of each breath does not participate in gas exchange. Higher fractions indicate impaired ventilation efficiency and are observed in various respiratory disorders.
MCQ 10 (Clinical):
In which situation would physiological dead space decrease?
a) Pulmonary embolism
b) Severe emphysema
c) Hyperventilation
d) Acute respiratory distress syndrome
Answer & Explanation:
Correct answer: c) Hyperventilation.
Explanation: During hyperventilation, increased respiratory rate reduces the relative proportion of dead space compared to tidal volume, temporarily lowering the dead space fraction. However, chronic respiratory diseases typically increase physiological dead space due to ventilation-perfusion mismatch and alveolar destruction.
Chapter: Respiratory Physiology
Topic: Pulmonary Function Tests
Subtopic: Maximum Voluntary Ventilation (MVV)
Keywords:
Maximum Voluntary Ventilation (MVV): The greatest amount of air that can be inhaled and exhaled within one minute during rapid, deep breathing.
Minute Ventilation: The volume of air breathed in one minute during normal breathing (TV × Respiratory Rate).
Forced Vital Capacity (FVC): The total volume of air that can be forcefully exhaled after full inspiration.
Obstructive Lung Disease: Disorders that block airflow and make breathing difficult (e.g., COPD, asthma).
Lead Question - 2013:
Maximum voluntary ventilation is -
a) 25 L/min
b) 50 L/min
c) 100 L/min
d) 150 L/min
Answer & Explanation:
Correct answer: c) 100 L/min.
Explanation: Maximum voluntary ventilation (MVV) measures the maximal amount of air a person can breathe in and out in one minute through rapid, deep breathing. In healthy adults, MVV typically ranges around 100 L/min. This test assesses respiratory muscle strength, airway resistance, and lung compliance in both clinical and research settings.
MCQ 1:
What does Maximum Voluntary Ventilation primarily assess?
a) Gas exchange efficiency
b) Respiratory muscle strength
c) Alveolar oxygen pressure
d) Arterial blood pH
Answer & Explanation:
Correct answer: b) Respiratory muscle strength.
Explanation: MVV assesses the strength and endurance of respiratory muscles, airway resistance, and lung compliance. A reduced MVV can suggest respiratory muscle weakness or obstructive lung disease. It helps differentiate between restrictive and obstructive respiratory pathologies during clinical evaluation.
MCQ 2 (Clinical):
A patient with severe COPD is likely to have which of the following MVV results?
a) Increased MVV
b) Normal MVV
c) Decreased MVV
d) MVV unaffected
Answer & Explanation:
Correct answer: c) Decreased MVV.
Explanation: COPD is an obstructive lung disease characterized by airway narrowing, increased airway resistance, and air trapping. These factors reduce the ability to perform rapid deep breaths, leading to significantly decreased MVV, serving as an important clinical indicator of disease severity.
MCQ 3:
Which of the following factors does NOT influence MVV?
a) Respiratory muscle strength
b) Lung compliance
c) Airway resistance
d) Arterial oxygen content
Answer & Explanation:
Correct answer: d) Arterial oxygen content.
Explanation: MVV depends primarily on respiratory muscle strength, lung compliance, and airway resistance. Arterial oxygen content does not directly affect the mechanical ability to breathe in and out rapidly but reflects gas exchange efficiency, which is assessed separately in pulmonary function tests.
MCQ 4 (Clinical):
Why is MVV useful in preoperative assessments?
a) Measures cardiac output
b) Evaluates pulmonary reserve
c) Determines blood glucose
d) Assesses renal function
Answer & Explanation:
Correct answer: b) Evaluates pulmonary reserve.
Explanation: MVV testing helps estimate a patient’s pulmonary reserve before surgery. A low MVV may indicate a higher risk of postoperative respiratory complications. Assessing MVV ensures optimal perioperative management by guiding anesthetic and ventilatory strategies to prevent hypoventilation or respiratory failure.
MCQ 5:
Which equation represents the relationship in Boyle's Law?
a) PV = constant
b) P/T = constant
c) V/T = constant
d) PV = nRT
Answer & Explanation:
Correct answer: a) PV = constant.
Explanation: Boyle’s Law states that at constant temperature, the pressure (P) of a gas is inversely proportional to its volume (V), expressed as PV = constant. This principle explains lung inflation and deflation mechanics during breathing cycles and is foundational in respiratory physiology.
MCQ 6 (Clinical):
Which patient condition could result in abnormally low MVV?
a) Emphysema
b) Asthma
c) Myasthenia gravis
d) Normal lung function
Answer & Explanation:
Correct answer: c) Myasthenia gravis.
Explanation: Myasthenia gravis causes muscle weakness, including respiratory muscles, reducing the ability to perform sustained or forceful breathing required in MVV tests. Such a low MVV helps clinicians detect neuromuscular involvement and distinguish it from primary pulmonary disorders.
MCQ 7:
Which of the following best describes Tidal Volume (TV)?
a) Volume during deep breathing
b) Volume exchanged during normal breathing
c) Air remaining after expiration
d) Maximum air exhaled forcefully
Answer & Explanation:
Correct answer: b) Volume exchanged during normal breathing.
Explanation: Tidal Volume (TV) is the volume of air moved in or out of the lungs during a normal, relaxed breath, typically around 500 mL in adults. It is essential for maintaining regular gas exchange and ventilation during everyday activities.
MCQ 8 (Clinical):
In which scenario is MVV measurement contraindicated?
a) Asthma exacerbation
b) Routine health checkup
c) Controlled COPD
d) Preoperative evaluation
Answer & Explanation:
Correct answer: a) Asthma exacerbation.
Explanation: During an asthma attack, forced and rapid breathing is unsafe and can worsen bronchospasm. Measuring MVV in this condition is contraindicated as it may provoke respiratory distress, worsen hypoxia, and is not diagnostically useful during acute episodes.
MCQ 9:
What is a typical MVV value for a healthy adult male?
a) 25 L/min
b) 50 L/min
c) 100 L/min
d) 150 L/min
Answer & Explanation:
Correct answer: c) 100 L/min.
Explanation: The normal maximum voluntary ventilation (MVV) in healthy adults is approximately 100 L/min. Values significantly lower suggest respiratory muscle weakness, lung disease, or neuromuscular disorders, making MVV a valuable clinical diagnostic tool.
MCQ 10 (Clinical):
Which intervention can improve MVV in a patient with chronic lung disease?
a) Pulmonary rehabilitation
b) High-dose corticosteroids
c) Restrictive diets
d) Beta-blockers
Answer & Explanation:
Correct answer: a) Pulmonary rehabilitation.
Explanation: Pulmonary rehabilitation, including breathing exercises, physical training, and education, improves respiratory muscle strength, endurance, and lung function, thereby increasing MVV in patients with chronic obstructive pulmonary diseases. It enhances quality of life and decreases hospitalizations.
Chapter: Respiratory Physiology
Topic: Lung Volumes and Capacities
Subtopic: Residual Volume and Functional Residual Capacity
Keywords:
Tidal Volume (TV): The volume of air inhaled or exhaled during normal, relaxed breathing.
Residual Volume (RV): The amount of air remaining in the lungs after a maximal exhalation, preventing lung collapse.
Functional Residual Capacity (FRC): The volume of air remaining in the lungs after normal expiration (FRC = RV + Expiratory Reserve Volume).
Vital Capacity (VC): The maximum volume of air that can be exhaled after a maximal inhalation.
Lead Question - 2013:
Air remaining in lung after normal expiration?
a) TV
b) RV
c) FRC
d) VC
Answer & Explanation:
Correct answer: c) FRC.
Explanation: Functional Residual Capacity (FRC) refers to the amount of air remaining in the lungs after a normal expiration. It consists of the Residual Volume (RV) plus Expiratory Reserve Volume (ERV). FRC prevents alveolar collapse by maintaining a constant volume and helps in gas exchange between breaths.
MCQ 1:
Which of the following is NOT part of Functional Residual Capacity?
a) Residual Volume
b) Expiratory Reserve Volume
c) Tidal Volume
d) None of the above
Answer & Explanation:
Correct answer: c) Tidal Volume.
Explanation: FRC is the volume of air in the lungs at the end of normal expiration and consists of Residual Volume and Expiratory Reserve Volume. Tidal Volume is the air exchanged during normal breathing and is not part of FRC, as it is actively involved in each breath cycle.
MCQ 2 (Clinical):
Which measurement is most reduced in restrictive lung disease?
a) Residual Volume
b) Functional Residual Capacity
c) Vital Capacity
d) Tidal Volume
Answer & Explanation:
Correct answer: c) Vital Capacity.
Explanation: Restrictive lung diseases, such as pulmonary fibrosis, decrease lung compliance and overall lung volumes. Vital Capacity (VC) is most affected as total lung capacity reduces significantly. FRC and RV may also be reduced but VC shows the most pronounced change clinically, indicating poor lung expansion ability.
MCQ 3:
Which is the primary purpose of Residual Volume?
a) Maximizes oxygen intake
b) Prevents alveolar collapse
c) Facilitates gas exchange
d) Regulates pH balance
Answer & Explanation:
Correct answer: b) Prevents alveolar collapse.
Explanation: Residual Volume (RV) ensures a constant volume of air remains in the lungs even after maximal exhalation. This prevents alveolar collapse (atelectasis) and maintains continuous gas exchange between breaths. Boyle's Law explains that a stable intrapulmonary volume avoids drastic pressure changes and keeps lungs inflated.
MCQ 4 (Clinical):
Which lung volume measurement is useful to detect obstructive lung disease?
a) Residual Volume
b) Functional Residual Capacity
c) Tidal Volume
d) Inspiratory Reserve Volume
Answer & Explanation:
Correct answer: a) Residual Volume.
Explanation: Obstructive lung diseases (e.g., COPD, asthma) impair air exhalation, causing an increase in Residual Volume (RV) and Functional Residual Capacity (FRC). Elevated RV indicates trapped air due to airway obstruction, helping in early diagnosis and appropriate management of these conditions.
MCQ 5:
Which lung capacity represents the total air volume after maximum inspiration?
a) Residual Volume
b) Functional Residual Capacity
c) Total Lung Capacity
d) Tidal Volume
Answer & Explanation:
Correct answer: c) Total Lung Capacity.
Explanation: Total Lung Capacity (TLC) is the maximum volume of air the lungs can hold, including Residual Volume (RV), Tidal Volume (TV), Inspiratory Reserve Volume (IRV), and Expiratory Reserve Volume (ERV). It indicates overall lung health and capacity to ventilate adequately.
MCQ 6 (Clinical):
Which condition is associated with an increased Functional Residual Capacity (FRC)?
a) Pulmonary fibrosis
b) Obstructive lung disease
c) Acute respiratory distress syndrome
d) Pneumonia
Answer & Explanation:
Correct answer: b) Obstructive lung disease.
Explanation: Obstructive diseases like emphysema cause air trapping, increasing FRC. This reflects impaired expiratory airflow and helps distinguish obstructive from restrictive diseases. Elevated FRC worsens gas exchange and leads to dyspnea and exercise intolerance in chronic conditions.
MCQ 7:
Which lung volume is not directly measurable by spirometry?
a) Tidal Volume
b) Residual Volume
c) Expiratory Reserve Volume
d) Inspiratory Capacity
Answer & Explanation:
Correct answer: b) Residual Volume.
Explanation: Residual Volume (RV) cannot be measured by spirometry as it represents the air left in lungs after maximum exhalation. Special techniques like helium dilution or body plethysmography are required. This understanding helps evaluate restrictive and obstructive disorders accurately.
MCQ 8 (Clinical):
What happens to FRC during anesthesia?
a) Increases
b) Decreases
c) Remains unchanged
d) Fluctuates unpredictably
Answer & Explanation:
Correct answer: b) Decreases.
Explanation: Anesthesia reduces muscle tone and chest wall expansion, lowering Functional Residual Capacity (FRC). This can cause alveolar collapse (atelectasis) and impaired gas exchange. Awareness of this helps anesthesiologists optimize ventilation and prevent hypoxia during surgery.
MCQ 9:
Which is correct regarding Functional Residual Capacity?
a) Equals TV + RV
b) Equals IRV + ERV
c) Equals RV + ERV
d) Equals TLC - RV
Answer & Explanation:
Correct answer: c) Equals RV + ERV.
Explanation: Functional Residual Capacity (FRC) is the volume of air in lungs after normal expiration and comprises Residual Volume (RV) plus Expiratory Reserve Volume (ERV). This is crucial in maintaining gas exchange during the breathing cycle and avoiding alveolar collapse.
MCQ 10 (Clinical):
Why is knowledge of lung volumes important in critical care?
a) To set ventilator parameters
b) To diagnose heart diseases
c) To measure blood glucose
d) To assess kidney function
Answer & Explanation:
Correct answer: a) To set ventilator parameters.
Explanation: Lung volumes, especially FRC and VC, guide mechanical ventilation settings. Knowledge of these parameters prevents overdistension, atelectasis, or hypoventilation, crucial for patient safety in ICU settings. Clinicians use lung volume data to customize respiratory support accurately.
Chapter: Respiratory Physiology
Topic: Gas Laws in Respiration
Subtopic: Boyle’s Law
Keywords:
Boyle’s Law: States that at constant temperature, the pressure and volume of a gas are inversely proportional (P × V = constant).
Charles’s Law: States that the volume of a gas is directly proportional to its absolute temperature at constant pressure (V/T = constant).
Ideal Gas Law: PV = nRT, relates pressure, volume, number of moles, gas constant, and temperature of a gas.
Pressure (P): The force exerted by gas molecules per unit area of container walls.
Volume (V): The space occupied by the gas.
Lead Question - 2013:
Boyle's Law states that ?
a) P/T = constant
b) PV = constant
c) PV = nRT
d) V/T = constant
Answer & Explanation:
Correct answer: b) PV = constant.
Explanation: Boyle's Law describes the inverse relationship between pressure (P) and volume (V) of a gas at constant temperature: when volume decreases, pressure increases proportionally, and vice versa. This principle explains the mechanics of lung inflation and deflation during breathing cycles in respiratory physiology.
MCQ 1:
Charles’s Law states that ?
a) P/T = constant
b) PV = constant
c) V/T = constant
d) P + V = constant
Answer & Explanation:
Correct answer: c) V/T = constant.
Explanation: Charles's Law states that the volume (V) of a gas is directly proportional to its absolute temperature (T) when pressure is constant. This explains how lung volume changes during breathing, especially in temperature regulation and understanding gas behavior in different respiratory conditions.
MCQ 2 (Clinical):
In emphysema, the lung compliance is:
a) Increased due to alveolar wall destruction
b) Decreased due to fibrosis
c) Normal
d) Increased due to bronchoconstriction
Answer & Explanation:
Correct answer: a) Increased due to alveolar wall destruction.
Explanation: In emphysema, destruction of alveolar walls reduces elastic recoil, increasing lung compliance. Boyle's Law helps explain how alveolar expansion occurs easily but leads to inefficient ventilation due to poor elastic recoil, causing air trapping and impaired gas exchange.
MCQ 3:
Which law relates to pressure, volume, and temperature of gas together?
a) Boyle’s Law
b) Charles’s Law
c) Ideal Gas Law
d) Avogadro’s Law
Answer & Explanation:
Correct answer: c) Ideal Gas Law.
Explanation: The Ideal Gas Law (PV = nRT) relates pressure, volume, and temperature of a gas together, considering the number of moles and gas constant. It applies to respiratory gas exchange and mechanical ventilation, providing a comprehensive understanding of gas behavior in the lungs.
MCQ 4 (Clinical):
Which condition reduces lung compliance?
a) Pulmonary fibrosis
b) Emphysema
c) Bronchiectasis
d) Asthma
Answer & Explanation:
Correct answer: a) Pulmonary fibrosis.
Explanation: Pulmonary fibrosis stiffens lung tissue due to collagen deposition, reducing compliance. Boyle's Law explains that increased stiffness resists volume changes despite pressure variations, leading to difficulty in lung expansion during inspiration and causing breathlessness.
MCQ 5:
At constant temperature, when lung volume increases, pressure inside the alveoli:
a) Increases
b) Remains constant
c) Decreases
d) Fluctuates randomly
Answer & Explanation:
Correct answer: c) Decreases.
Explanation: According to Boyle's Law, during inspiration, diaphragm contracts, thoracic volume increases, and alveolar pressure decreases below atmospheric pressure. This pressure gradient drives air into the lungs, illustrating the inverse relationship between pressure and volume at constant temperature.
MCQ 6 (Clinical):
Which of the following is true during mechanical ventilation?
a) Boyle's Law does not apply
b) Volume is constant despite pressure changes
c) Pressure and volume changes follow Boyle's Law
d) Temperature varies significantly
Answer & Explanation:
Correct answer: c) Pressure and volume changes follow Boyle's Law.
Explanation: Mechanical ventilators apply pressure to inflate lungs; Boyle's Law governs how pressure increases lead to proportional volume expansion. Understanding this helps optimize ventilator settings, prevent barotrauma, and ensure adequate alveolar ventilation without damaging lung tissues.
MCQ 7:
Which is NOT a key variable in Boyle’s Law?
a) Pressure
b) Volume
c) Temperature
d) Gas constant
Answer & Explanation:
Correct answer: c) Temperature.
Explanation: Boyle's Law applies when temperature is constant (isothermal conditions). It only relates pressure and volume inversely. Temperature changes are considered in Charles’s Law or the Ideal Gas Law, so Boyle's Law focuses purely on pressure-volume relationship in the lungs during normal breathing.
MCQ 8 (Clinical):
Why is Boyle's Law significant during anesthesia?
a) It helps calculate drug dosage
b) Explains gas expansion in body cavities
c) Predicts cardiac output
d) Determines renal filtration rate
Answer & Explanation:
Correct answer: b) Explains gas expansion in body cavities.
Explanation: Boyle’s Law explains how gas expands when pressure decreases, crucial in anesthesia where gas-filled spaces (e.g., pneumothorax, intestines) may expand dangerously. Proper understanding prevents complications by adjusting ventilator pressures to avoid overexpansion.
MCQ 9:
In which situation does Boyle’s Law apply during respiration?
a) Airflow during forced expiration
b) Air entering lungs during inspiration
c) Blood flow in pulmonary circulation
d) Oxygen binding to hemoglobin
Answer & Explanation:
Correct answer: b) Air entering lungs during inspiration.
Explanation: During inspiration, thoracic cavity volume increases, alveolar pressure decreases, and air flows from higher to lower pressure. Boyle’s Law (P × V = constant) precisely describes this fundamental principle of normal breathing mechanics in pulmonary physiology.
MCQ 10 (Clinical):
In pneumothorax, Boyle’s Law explains that:
a) Lung volume increases due to external pressure
b) Air enters pleural space lowering intrapleural pressure
c) Loss of negative intrapleural pressure causes lung collapse
d) Gas laws are irrelevant
Answer & Explanation:
Correct answer: c) Loss of negative intrapleural pressure causes lung collapse.
Explanation: Boyle’s Law explains that when intrapleural pressure rises (air enters pleural space), pressure difference disappears, and lungs collapse as volume can’t expand. This understanding is crucial in diagnosing and managing pneumothorax with chest tube drainage to restore negative pressure and lung function.
Chapter: Respiratory Physiology
Topic: Pulmonary Function Tests
Subtopic: Vital Capacity
Keywords:
Vital Capacity (VC): Maximum amount of air exhaled after maximum inspiration, important for respiratory health assessment.
Tidal Volume: Volume of air inhaled and exhaled in normal breathing (~500 ml).
Inspiratory Reserve Volume (IRV): Additional air inhaled beyond tidal volume during deep inspiration.
Expiratory Reserve Volume (ERV): Additional air exhaled beyond tidal volume during forceful expiration.
Residual Volume (RV): Air remaining in lungs after maximal exhalation, not part of vital capacity.
Lead Question - 2013:
Normal vital capacity in an adult is -
a) 1200 ml
b) 2500 ml
c) 3000 ml
d) 4700 ml
Answer & Explanation:
Correct answer: d) 4700 ml.
Explanation: Vital capacity (VC) reflects the maximal air volume a person can expel from the lungs after a maximal inhalation. In a healthy adult, the normal VC typically ranges between 4000-5000 ml, depending on age, sex, and body size. It is critical for assessing respiratory function during pulmonary function tests.
MCQ 1:
Tidal volume in a healthy adult averages approximately:
a) 150 ml
b) 300 ml
c) 500 ml
d) 750 ml
Answer & Explanation:
Correct answer: c) 500 ml.
Explanation: Tidal volume (TV) is the volume of air exchanged during normal, quiet breathing. In healthy adults, this averages about 500 ml per breath. TV reflects baseline ventilation, critical for maintaining adequate gas exchange at rest without involving inspiratory or expiratory reserve volumes.
MCQ 2 (Clinical):
Which pulmonary function test parameter indicates obstructive lung disease?
a) Increased VC
b) Decreased FEV1/FVC ratio
c) Increased RV
d) Decreased IRV
Answer & Explanation:
Correct answer: b) Decreased FEV1/FVC ratio.
Explanation: Obstructive lung diseases like COPD and asthma cause airflow limitation. The forced expiratory volume in 1 second (FEV1) reduces significantly compared to the forced vital capacity (FVC), resulting in a decreased FEV1/FVC ratio, essential for diagnosing obstructive patterns during spirometry.
MCQ 3:
Which of the following is NOT part of vital capacity?
a) Inspiratory Reserve Volume (IRV)
b) Expiratory Reserve Volume (ERV)
c) Residual Volume (RV)
d) Tidal Volume (TV)
Answer & Explanation:
Correct answer: c) Residual Volume (RV).
Explanation: Vital capacity (VC) includes tidal volume (TV), inspiratory reserve volume (IRV), and expiratory reserve volume (ERV). Residual volume (RV) is the air remaining in lungs after maximal exhalation and cannot be voluntarily expelled, hence not included in VC calculations.
MCQ 4 (Clinical):
Which condition leads to reduced vital capacity?
a) Emphysema
b) Restrictive lung disease
c) Asthma
d) Pneumothorax
Answer & Explanation:
Correct answer: b) Restrictive lung disease.
Explanation: In restrictive lung diseases (e.g., pulmonary fibrosis), lung expansion is impaired, decreasing lung volumes including vital capacity. Patients experience reduced VC and total lung capacity, leading to increased respiratory effort, dyspnea, and compromised oxygen exchange due to stiff, non-compliant lung tissue.
MCQ 5:
What does the inspiratory reserve volume (IRV) represent?
a) Volume exhaled during forced expiration
b) Additional air inhaled after normal inspiration
c) Air remaining in lungs after full expiration
d) Volume inhaled during quiet breathing
Answer & Explanation:
Correct answer: b) Additional air inhaled after normal inspiration.
Explanation: Inspiratory Reserve Volume (IRV) refers to the extra air a person can inhale beyond the tidal volume during deep inspiration. It reflects lung elasticity and inspiratory muscle strength and is important in assessing respiratory reserve and overall pulmonary function.
MCQ 6 (Clinical):
Reduced vital capacity in obesity is mainly due to:
a) Decreased respiratory muscle strength
b) Increased airway resistance
c) Reduced lung compliance due to fat deposition
d) Loss of alveolar surfactant
Answer & Explanation:
Correct answer: c) Reduced lung compliance due to fat deposition.
Explanation: Obesity restricts chest wall and diaphragm movement because of fat deposition, reducing lung compliance and vital capacity. Patients experience increased work of breathing and reduced functional residual capacity, potentially causing hypoventilation and decreased oxygenation.
MCQ 7:
What is typical residual volume in healthy adults?
a) 500 ml
b) 1200 ml
c) 1500 ml
d) 2000 ml
Answer & Explanation:
Correct answer: b) 1200 ml.
Explanation: Residual Volume (RV) is the volume of air remaining in the lungs after maximal expiration. Typically around 1200 ml in healthy adults, RV prevents alveolar collapse and maintains gas exchange between breaths, measured indirectly during pulmonary function tests.
MCQ 8 (Clinical):
In which condition does vital capacity improve after bronchodilator use?
a) Restrictive lung disease
b) Asthma
c) Pulmonary fibrosis
d) Pneumonia
Answer & Explanation:
Correct answer: b) Asthma.
Explanation: Asthma causes reversible airway obstruction. Bronchodilators relax bronchial smooth muscle, improve airflow, and increase vital capacity by reducing airway resistance. Pulmonary fibrosis and other restrictive disorders do not respond to bronchodilators, as the problem lies in lung parenchyma stiffness.
MCQ 9:
Which factor affects vital capacity?
a) Age
b) Sex
c) Body size
d) All of the above
Answer & Explanation:
Correct answer: d) All of the above.
Explanation: Vital capacity varies with age, sex, and body size. Young, tall males generally have higher VC due to larger thoracic volume and stronger respiratory muscles. Aging and restrictive diseases reduce VC due to decreased elasticity and muscle strength.
MCQ 10 (Clinical):
Which measurement is commonly reduced in restrictive lung disease?
a) Vital Capacity
b) FEV1/FVC ratio
c) Residual Volume
d) Tidal Volume
Answer & Explanation:
Correct answer: a) Vital Capacity.
Explanation: Restrictive lung disease reduces total lung volumes, especially vital capacity, due to limited lung expansion from fibrosis or structural deformities. FEV1/FVC ratio remains normal or increases because both FEV1 and FVC decrease proportionally, distinguishing restrictive from obstructive patterns.
Chapter: Respiratory Physiology
Topic: Mechanism of Breathing
Subtopic: Pulmonary Mechanics and Gas Exchange
Keywords:
Transpulmonary Pressure: Difference between alveolar pressure and pleural pressure, important for lung expansion.
Compliance: Measure of lung distensibility, determined by elasticity and surfactant presence.
Surfactant: Surface-active agent produced by alveolar cells to reduce surface tension, aiding lung expansion.
Passive Expiration: Relaxation of respiratory muscles allowing elastic recoil of lungs during quiet breathing.
Active Inspiration: Involves contraction of diaphragm and external intercostal muscles to draw air into lungs.
Lead Question - 2013:
True about breathing are all except?
a) Normal breathing occurs when transpulmonary pressure is 8-5 cm H2O
b) Compliance depends only on surfactant
c) Expiration during quiet breathing is passive
d) Inspiration is an active process
Answer & Explanation:
Correct answer: b) Compliance depends only on surfactant.
Explanation: Pulmonary compliance depends on both the elastic properties of lung tissue and the presence of surfactant, not surfactant alone. Transpulmonary pressure drives lung expansion. Quiet expiration is passive due to elastic recoil, and inspiration is active via muscular contraction. This coordination maintains effective ventilation.
MCQ 1:
Which muscle is primarily responsible for quiet inspiration?
a) Diaphragm
b) Internal intercostal
c) Abdominal muscles
d) Sternocleidomastoid
Answer & Explanation:
Correct answer: a) Diaphragm.
Explanation: The diaphragm contracts and flattens during quiet inspiration, increasing thoracic volume and reducing intrathoracic pressure, facilitating air entry into the lungs. Internal intercostals and accessory muscles participate during forced breathing, but the diaphragm remains the primary muscle during restful breathing.
MCQ 2 (Clinical):
Which condition reduces lung compliance?
a) Pulmonary fibrosis
b) Emphysema
c) Asthma
d) Bronchitis
Answer & Explanation:
Correct answer: a) Pulmonary fibrosis.
Explanation: Pulmonary fibrosis causes stiff, scarred lung tissue, significantly reducing compliance. Patients exhibit increased work of breathing and reduced gas exchange efficiency. Emphysema, conversely, increases compliance due to loss of elastic recoil, making inhalation easier but compromising exhalation and gas exchange.
MCQ 3:
What is the primary role of surfactant in the lungs?
a) Increase alveolar surface tension
b) Reduce alveolar surface tension
c) Facilitate gas diffusion
d) Prevent blood clot formation
Answer & Explanation:
Correct answer: b) Reduce alveolar surface tension.
Explanation: Surfactant, secreted by alveolar type II cells, reduces surface tension within alveoli, preventing their collapse during expiration and lowering the work required for inflation. This mechanism enhances lung compliance and ensures uniform alveolar expansion during inspiration and exhalation.
MCQ 4 (Clinical):
In which disease is surfactant production insufficient in neonates?
a) Neonatal Respiratory Distress Syndrome
b) Cystic fibrosis
c) Pneumonia
d) Asthma
Answer & Explanation:
Correct answer: a) Neonatal Respiratory Distress Syndrome.
Explanation: Premature infants often have underdeveloped lungs with insufficient surfactant production, leading to alveolar collapse, poor gas exchange, and respiratory distress. Treatment includes exogenous surfactant administration and respiratory support to reduce morbidity and mortality in affected neonates.
MCQ 5:
Which factor primarily drives normal quiet expiration?
a) Active muscle contraction
b) Elastic recoil of lungs
c) Diaphragm contraction
d) Surfactant secretion
Answer & Explanation:
Correct answer: b) Elastic recoil of lungs.
Explanation: During quiet expiration, the diaphragm and external intercostal muscles relax, and the elastic properties of lung tissue cause passive expulsion of air. Active expiration involves abdominal and internal intercostal muscle contraction during forced breathing.
MCQ 6 (Clinical):
Transpulmonary pressure is calculated as:
a) Alveolar pressure minus atmospheric pressure
b) Intrapleural pressure minus alveolar pressure
c) Alveolar pressure minus intrapleural pressure
d) Atmospheric pressure minus intrapleural pressure
Answer & Explanation:
Correct answer: c) Alveolar pressure minus intrapleural pressure.
Explanation: Transpulmonary pressure (Ptp) represents the distending pressure that keeps lungs open. It is calculated by subtracting intrapleural pressure (Pip) from alveolar pressure (Pa): Ptp = Pa - Pip. Proper Ptp ensures adequate lung expansion during inspiration and prevents collapse during expiration.
MCQ 7:
In obstructive lung disease, compliance is typically:
a) Increased
b) Decreased
c) Unchanged
d) Variable
Answer & Explanation:
Correct answer: a) Increased.
Explanation: Obstructive lung diseases like emphysema damage elastic fibers, increasing compliance as lungs become more distensible. However, this increased compliance does not improve function; it impairs elastic recoil, leading to air trapping and inefficient ventilation, contributing to respiratory insufficiency.
MCQ 8 (Clinical):
What is the effect of pulmonary surfactant deficiency in adults?
a) Asthma
b) Acute Respiratory Distress Syndrome (ARDS)
c) Chronic bronchitis
d) Tuberculosis
Answer & Explanation:
Correct answer: b) Acute Respiratory Distress Syndrome (ARDS).
Explanation: In ARDS, surfactant production decreases due to alveolar damage, leading to increased surface tension, alveolar collapse, and impaired gas exchange. Management includes mechanical ventilation and exogenous surfactant replacement in severe cases to improve oxygenation.
MCQ 9:
Which pressure difference is critical for alveolar inflation?
a) Atmospheric pressure - alveolar pressure
b) Alveolar pressure - intrapleural pressure
c) Atmospheric pressure - intrapleural pressure
d) Intrapleural pressure - atmospheric pressure
Answer & Explanation:
Correct answer: b) Alveolar pressure - intrapleural pressure.
Explanation: The transpulmonary pressure difference (Pa - Pip) determines alveolar expansion during inspiration. It must remain positive to prevent lung collapse and allow air inflow. Proper balance of pressures ensures adequate ventilation and gas exchange.
MCQ 10 (Clinical):
Which condition increases work of breathing significantly?
a) Pneumothorax
b) Normal breathing
c) Hyperventilation
d) Increased lung compliance
Answer & Explanation:
Correct answer: a) Pneumothorax.
Explanation: Pneumothorax causes loss of negative intrapleural pressure, lung collapse, and increased work of breathing due to impaired alveolar expansion. Immediate medical intervention is required to restore pleural integrity and reduce respiratory distress.
Chapter: Respiratory System
Topic: Respiratory Failure
Subtopic: Classification and Causes of Respiratory Failure
Keywords:
Respiratory Failure: Condition where the respiratory system fails to maintain adequate gas exchange, leading to hypoxemia or hypercapnia.
Type 3 Respiratory Failure: Perioperative respiratory failure primarily caused by postoperative atelectasis leading to impaired gas exchange.
Atelectasis: Collapse of alveoli in the lung, reducing gas exchange surface area, often post-surgery or due to obstruction.
Kyphoscoliosis: Abnormal curvature of the spine causing restrictive lung disease and chronic hypoventilation.
Flail Chest: Segment of the thoracic cage breaks, impairs ventilation, and leads to respiratory distress.
Pulmonary Fibrosis: Progressive lung scarring reducing lung compliance and causing chronic hypoxia.
Lead Question - 2013:
Type 3 respiratory failure occurs due to ?
a) Post-operative atelectasis
b) Kyphoscoliosis
c) Flail chest
d) Pulmonary fibrosis
Answer & Explanation:
Correct answer: a) Post-operative atelectasis.
Explanation: Type 3 respiratory failure refers to perioperative respiratory failure primarily caused by post-operative atelectasis. This condition reduces alveolar surface area, impairing gas exchange and leading to hypoxia and hypercapnia. It is common in surgeries involving the thoracic cavity or upper abdomen and requires proactive management to prevent complications.
MCQ 1:
Which type of respiratory failure is mainly due to alveolar hypoventilation?
a) Type 1
b) Type 2
c) Type 3
d) Type 4
Answer & Explanation:
Correct answer: b) Type 2.
Explanation: Type 2 respiratory failure involves alveolar hypoventilation, causing both hypoxemia and hypercapnia. It is often due to respiratory muscle weakness, CNS depression, or obstructive diseases. Monitoring PaCO2 levels and using ventilatory support are essential management strategies in these patients.
MCQ 2 (Clinical):
Postoperative atelectasis commonly occurs due to:
a) Deep breathing exercises
b) Prolonged immobility
c) Early ambulation
d) Incentive spirometry
Answer & Explanation:
Correct answer: b) Prolonged immobility.
Explanation: Prolonged immobility post-surgery contributes to postoperative atelectasis by reducing deep breaths and leading to alveolar collapse. Preventive measures include incentive spirometry and early ambulation. Failure to address this may cause type 3 respiratory failure due to impaired gas exchange and hypoventilation.
MCQ 3:
Kyphoscoliosis leads to which type of respiratory impairment?
a) Obstructive
b) Restrictive
c) Mixed
d) None
Answer & Explanation:
Correct answer: b) Restrictive.
Explanation: Kyphoscoliosis causes restrictive lung disease by deforming the thoracic cage, decreasing lung expansion, and leading to hypoventilation. This contributes to chronic type 2 respiratory failure. Management includes respiratory physiotherapy and, in severe cases, ventilatory support to correct hypoxia and hypercapnia.
MCQ 4 (Clinical):
Flail chest causes respiratory failure due to:
a) Pneumothorax
b) Paradoxical movement
c) Pleural effusion
d) Bronchospasm
Answer & Explanation:
Correct answer: b) Paradoxical movement.
Explanation: Flail chest involves fracture of consecutive ribs, causing paradoxical movement during respiration. This leads to ineffective ventilation and hypoxia, contributing to type 2 respiratory failure. Supportive measures include oxygen therapy and mechanical ventilation if necessary to stabilize breathing and gas exchange.
MCQ 5:
Pulmonary fibrosis primarily affects:
a) Airways
b) Alveoli
c) Pleura
d) Bronchioles
Answer & Explanation:
Correct answer: b) Alveoli.
Explanation: Pulmonary fibrosis involves progressive scarring of alveolar tissue, reducing lung compliance and impairing oxygen diffusion. Though not classified as type 3 respiratory failure, it contributes to chronic hypoxia and, in advanced stages, leads to type 1 or type 2 respiratory failure.
MCQ 6 (Clinical):
Best intervention to prevent postoperative atelectasis is:
a) Bed rest
b) Incentive spirometry
c) Sedation
d) Diuretics
Answer & Explanation:
Correct answer: b) Incentive spirometry.
Explanation: Incentive spirometry encourages deep breathing to prevent alveolar collapse after surgery, reducing the risk of postoperative atelectasis and type 3 respiratory failure. It enhances lung expansion, improves oxygenation, and facilitates early mobilization, vital in perioperative care protocols.
MCQ 7:
Type 1 respiratory failure is characterized by:
a) Hypoxia without hypercapnia
b) Hypercapnia without hypoxia
c) Both hypoxia and hypercapnia
d) Normal blood gases
Answer & Explanation:
Correct answer: a) Hypoxia without hypercapnia.
Explanation: Type 1 respiratory failure results from diseases like ARDS or pneumonia causing impaired oxygenation without affecting carbon dioxide removal. Oxygen therapy is the primary treatment, focusing on correcting hypoxemia without ventilation support unless CO2 retention develops.
MCQ 8 (Clinical):
Which factor contributes most to Type 3 respiratory failure?
a) Chronic bronchitis
b) Postoperative atelectasis
c) COPD exacerbation
d) Asthma attack
Answer & Explanation:
Correct answer: b) Postoperative atelectasis.
Explanation: Type 3 respiratory failure, also termed perioperative respiratory failure, typically occurs due to postoperative atelectasis. It reduces effective alveolar ventilation, impairing oxygenation and causing hypoventilation. Proactive respiratory physiotherapy and monitoring reduce this risk during the perioperative period.
MCQ 9:
Which is a typical sign of Type 3 respiratory failure?
a) Severe dyspnea
b) Hypoxia following surgery
c) Hypercapnia in asthma
d) Chronic cough
Answer & Explanation:
Correct answer: b) Hypoxia following surgery.
Explanation: Type 3 respiratory failure presents with hypoxia postoperatively due to atelectasis and reduced alveolar ventilation. It is critical to monitor postoperative patients for oxygen desaturation and respiratory effort changes, initiating timely interventions to prevent deterioration.
MCQ 10 (Clinical):
Management of Type 3 respiratory failure includes:
a) Oxygen therapy
b) Incentive spirometry
c) Non-invasive ventilation
d) All of the above
Answer & Explanation:
Correct answer: d) All of the above.
Explanation: Managing Type 3 respiratory failure involves oxygen therapy to correct hypoxemia, incentive spirometry to prevent or resolve atelectasis, and non-invasive ventilation if required. These strategies ensure effective alveolar ventilation and prevent progression to severe respiratory compromise.
Chapter: Anatomy
Topic: Thorax
Subtopic: Trachea and Bronchi
Keyword Definitions:
Right bronchus: Primary bronchus supplying right lung, shorter, wider, and more vertical than left.
Left bronchus: Narrower, longer, and more oblique, passes below the arch of aorta.
Carina: Ridge at tracheal bifurcation, highly sensitive, directs airflow.
Aspiration: Foreign bodies are more likely to lodge in right bronchus due to its alignment.
Bronchoscopy: Clinical procedure to visualize and manage airway pathologies.
Clinical relevance: Bronchial anatomy is crucial for intubation, aspiration, and radiology interpretation.
Lead Question - 2013
Not true about right bronchus
a) Shorter
b) Wider
c) More horizontal
d) In the line of trachea
Explanation: The right bronchus is shorter, wider, and more vertical, aligning with the trachea, making it a common site for aspirated foreign bodies. The statement “more horizontal” is false. Thus, the correct answer is c) More horizontal.
Guessed Question 2
Which bronchus is more prone to foreign body aspiration?
a) Left
b) Right
c) Both equally
d) Neither
Explanation: The right bronchus is wider, shorter, and more vertical, making it the commonest site for aspirated objects in adults and children. The correct answer is b) Right.
Guessed Question 3
Carina is located at which vertebral level?
a) T2
b) T4/T5
c) T6
d) T8
Explanation: The trachea bifurcates at the sternal angle (angle of Louis) corresponding to T4/T5 vertebral level, where the carina is located. The correct answer is b) T4/T5.
Guessed Question 4
The left bronchus passes beneath which vascular structure?
a) Aortic arch
b) Pulmonary trunk
c) SVC
d) Right atrium
Explanation: The left main bronchus runs under the arch of aorta and in front of the esophagus, making it longer and more oblique than the right bronchus. The correct answer is a) Aortic arch.
Guessed Question 5
In bronchoscopy, which structure indicates the division of bronchi?
a) Hilum
b) Carina
c) Trachealis muscle
d) Pulmonary ligament
Explanation: The carina is a ridge inside the trachea at the bifurcation into right and left bronchi. It is a key landmark in bronchoscopy and highly sensitive to stimulation. The correct answer is b) Carina.
Guessed Question 6
Which bronchus is longer?
a) Left
b) Right
c) Both equal
d) Depends on respiration
Explanation: The left main bronchus is longer (about 5 cm) compared to the right (2.5 cm), as it needs to cross structures like the aorta to reach the left lung. The correct answer is a) Left.
Guessed Question 7
A child aspirates a peanut. Where is it most likely to lodge?
a) Left main bronchus
b) Right main bronchus
c) Larynx
d) Esophagus
Explanation: Due to its wider, shorter, and more vertical orientation, the right bronchus is the most common site for foreign body aspiration. The correct answer is b) Right main bronchus.
Guessed Question 8
The right upper lobe bronchus branches off before?
a) Carina
b) Hilum
c) Right pulmonary artery
d) Right atrium
Explanation: The right upper lobe bronchus arises before the hilum of the right lung and above the right pulmonary artery, making the right bronchus eparterial. The correct answer is c) Right pulmonary artery.
Guessed Question 9
The left bronchus in relation to pulmonary artery is termed?
a) Eparterial
b) Hyparterial
c) Subarterial
d) Supraarterial
Explanation: The left bronchus lies inferior to the left pulmonary artery, hence it is termed hyparterial, while the right upper bronchus is eparterial. The correct answer is b) Hyparterial.
Guessed Question 10
During intubation, if tube enters right bronchus, what occurs?
a) Both lungs ventilated
b) Only right lung ventilated
c) Only left lung ventilated
d) No ventilation
Explanation: If the endotracheal tube goes too deep, it often enters the right bronchus, ventilating only the right lung, leading to hypoxia and left lung collapse. The correct answer is b) Only right lung ventilated.
Guessed Question 11
Which bronchus is more oblique in direction?
a) Right
b) Left
c) Both
d) Neither
Explanation: The left main bronchus is longer and runs more obliquely to reach the left lung, unlike the right bronchus which is more vertical. The correct answer is b) Left.
Keyword Definitions
• Central chemoreceptors: Medullary sensors responding to CSF pH/CO₂ changes and driving ventilation.
• Peripheral chemoreceptors: Carotid and aortic body receptors sensing arterial O₂, CO₂ and pH.
• Carotid body: Small chemo-sensitive organ at carotid bifurcation.
• Aortic body: Chemoreceptor tissue near aortic arch.
• Area postrema: Brainstem chemoreceptive region outside blood-brain barrier.
• Nucleus tractus solitarius (NTS): Medullary visceral sensory nucleus receiving vagal and glossopharyngeal afferents.
• Hypercapnia: Elevated arterial CO₂ stimulating central chemoreceptors.
• Hypoxia: Low arterial O₂ primarily stimulating peripheral chemoreceptors.
• Ventilatory drive: Neural control that adjusts rate and depth of breathing.
• Respiratory reflexes: Integrated responses coordinating breathing with cardiovascular state.
• Respiratory failure: Clinical condition from inadequate ventilation or gas exchange.
Chapter: Respiratory Physiology
Topic: Chemoreceptors and Respiratory Control
Subtopic: Central and Peripheral Chemoreceptors
Lead Question – 2012 (177)
Chemoreceptors are located in which area?
a) Medulla
b) Arch of aorta
c) Bifurcation of carotid artery
d) All of the above
Explanation: Chemoreceptors that regulate ventilation are both central and peripheral: central receptors in the medulla sense CSF pH changes from CO₂; peripheral chemoreceptors reside in the carotid bifurcation and aortic arch sensing arterial O₂, CO₂ and pH. They act together to regulate breathing. Answer: d) All of the above.
Question 2
Central chemoreceptors primarily respond to which stimulus?
a) Arterial O₂ fall
b) CSF pH change due to CO₂ diffusion
c) Blood glucose levels
d) Systemic blood pressure changes
Explanation: Central chemoreceptors in the ventrolateral medulla detect changes in CSF pH produced by CO₂ diffusion across the blood-brain barrier. This mechanism drives ventilation in response to hypercapnia and maintains acid-base homeostasis. Peripheral O₂ sensing is separate. Answer: b) CSF pH change due to CO₂ diffusion.
Question 3
Peripheral chemoreceptors that sense hypoxia at the carotid bifurcation transmit via which nerve?
a) Vagus nerve (X)
b) Glossopharyngeal nerve (IX)
c) Hypoglossal nerve (XII)
d) Facial nerve (VII)
Explanation: Carotid body afferents travel in the glossopharyngeal nerve (cranial nerve IX) to the nucleus tractus solitarius, which relays to respiratory centers, producing rapid ventilatory responses to hypoxia. Answer: b) Glossopharyngeal nerve (IX).
Question 4
Aortic body chemoreceptors convey information primarily via which pathway?
a) Glossopharyngeal nerve (IX) only
b) Vagus nerve (X) afferents
c) Trigeminal nerve (V) afferents
d) Direct spinal tract only
Explanation: Aortic arch chemoreceptors send afferent signals largely through vagal (X) fibers to the nucleus tractus solitarius in the medulla, complementing carotid body input to adjust ventilation and autonomic reflexes. Answer: b) Vagus nerve (X) afferents.
Question 5
Which chemoreceptor set predominates in response to acute hypoxemia?
a) Central medullary chemoreceptors
b) Peripheral carotid chemoreceptors
c) Renal chemoreceptors
d) Cortical chemoreceptors
Explanation: Peripheral carotid chemoreceptors are the primary detectors of arterial hypoxemia, responding rapidly to low PaO₂ and increasing ventilation quickly; central chemoreceptors mainly respond to CO₂/pH changes. Answer: b) Peripheral carotid chemoreceptors.
Question 6
Which condition blunts the ventilatory response to hypoxia due to carotid body removal or dysfunction?
a) Enhanced hypoxic drive
b) Diminished hypoxic ventilatory response
c) Increased cough reflex
d) Hyperventilation at rest
Explanation: Loss or dysfunction of carotid bodies reduces the rapid ventilatory response to hypoxia, causing a blunted hypoxic ventilatory drive clinically; patients rely more on central CO₂ sensitivity, risking inadequate ventilation during low oxygen states. Answer: b) Diminished hypoxic ventilatory response.
Question 7
Drugs that depress central chemoreceptor sensitivity commonly cause which effect?
a) Tachypnea
b) Hypoventilation and hypercapnia
c) Increased oxygen saturation
d) Enhanced hypoxic drive
Explanation: Sedatives and opioids depress central chemoreceptor responsiveness, reducing ventilatory drive to CO₂ and causing hypoventilation with rising arterial CO₂ and respiratory acidosis; careful monitoring and dose adjustment are clinically required. Answer: b) Hypoventilation and hypercapnia.
Question 8
Which bedside test best evaluates peripheral chemoreceptor function?
a) Hypercapnic ventilatory challenge
b) Hypoxic ventilatory response testing
c) Valsalva maneuver only
d) Pupillary reflex testing
Explanation: Hypoxic ventilatory response testing assesses peripheral chemoreceptor sensitivity by measuring ventilation changes when inspired oxygen is lowered; it helps distinguish peripheral dysfunction from central CO₂ responsiveness. Answer: b) Hypoxic ventilatory response testing.
Question 9
Which pathology explains reduced central chemosensitivity causing sleep hypoventilation?
a) Medullary lesion or congenital central hypoventilation syndrome
b) Peripheral nerve entrapment
c) Middle ear infection
d) Muscle strain
Explanation: Central hypoventilation may arise from medullary damage or congenital central hypoventilation syndrome, impairing CO₂ detection and ventilation particularly during sleep, often necessitating ventilatory support. Answer: a) Medullary lesion or congenital central hypoventilation syndrome.
Question 10
Which combination best describes chemoreceptor roles?
a) Carotid bodies sense CO₂ only; medulla senses O₂ only
b) Peripheral receptors detect hypoxia quickly; central receptors monitor CO₂/pH continuously
c) Aortic arch controls consciousness; carotid bodies control heart rate only
d) None of the above
Explanation: Peripheral receptors (carotid and aortic bodies) detect hypoxia rapidly and signal ventilatory increase; central medullary chemoreceptors continuously monitor CO₂/pH to regulate baseline ventilation. Together they coordinate appropriate respiratory responses. Answer: b) Peripheral receptors detect hypoxia quickly; central receptors monitor CO₂/pH continuously.
Question 11
Which clinical statement is correct regarding chemoreceptor physiology?
a) Only central receptors respond to severe hypoxia
b) Peripheral receptors play no role in ventilatory adaptation at altitude
c) Both central and peripheral chemoreceptors integrate to control ventilation
d) Chemoreceptors exclusively control heart rate, not breathing
Explanation: Ventilatory control reflects integrated input from central and peripheral chemoreceptors, with each contributing specific sensitivity to CO₂/pH and O₂ changes; combined signaling ensures respiratory adaptation to metabolic demands, altitude, and disease states. Answer: c) Both central and peripheral chemoreceptors integrate to control ventilation.
Keywords (for all questions)
Diffusion: Movement of gas down partial pressure gradients across thin membranes.
Partial pressure (P): Driving force for gas transfer; P_O₂ and P_CO₂ determine direction and rate.
Capillary: Thin-walled microvessel providing maximal surface area for gas exchange.
Transit time: Time blood spends in capillary; affects equilibration of gases.
Fick’s law: Rate ∝ (diffusion coefficient × area × ΔP) / thickness.
Diffusion coefficient: Depends on gas solubility and molecular weight (CO₂ diffuses faster than O₂).
Diffusion distance: Separation between blood and tissue; increased by edema or fibrosis.
Capillary recruitment: More capillaries perfused increases exchange surface area (important in exercise).
Oxygen content vs PO₂: Content depends on hemoglobin concentration and saturation; PO₂ measures dissolved gas.
Diffusion limitation vs perfusion limitation: Diffusion-limited when membrane thickening limits equilibration; perfusion-limited when transit time limits uptake.
Clinical examples: Pulmonary fibrosis → diffusion limitation; anemia → low O₂ content; pulmonary edema → increased diffusion distance.
Chapter: Respiratory Physiology | Topic: Gas Exchange | Subtopic: Tissue Gas Exchange
Lead Question – 2012
Gas exchange in tissues takes place at ?
a) Artery
b) Capillary
c) Vein
d) Venules
Explanation: Gas exchange in tissues occurs across capillary walls where oxygen diffuses from blood to cells and carbon dioxide diffuses back into plasma. Capillaries provide thin endothelium and large surface area for diffusion; arterioles/venules serve as conduits. Thus exchange primarily occurs in capillaries. Answer: b) Capillary.
1) Which law best describes the rate of gas transfer across the capillary membrane?
a) Fick's law
b) Boyle's law
c) Henry's law
d) Charles's law
Explanation: Fick’s law quantifies net gas transfer across membranes: rate = (diffusion coefficient × area × partial pressure difference)/thickness. Increasing surface area or partial pressure gradient or diffusion coefficient, or decreasing membrane thickness, augments exchange. Clinically, emphysema reduces area, pulmonary fibrosis increases thickness, reducing oxygen transfer markedly. Answer: a) Fick’s law.
2) During strenuous exercise capillary transit time falls. What is the usual effect on O₂ uptake?
a) O₂ uptake falls drastically
b) Minimal effect due to compensation
c) Equilibration impossible
d) O₂ uptake becomes zero
Explanation: During exercise capillary transit time shortens due to increased cardiac output; despite reduced transit, elevated perfusion and larger partial pressure gradients maintain oxygen uptake by increased diffusion and recruitment of capillaries. In severe pathology, very short transit may limit saturation. Answer: b) Minimal effect due to compensation in healthy individuals.
3) Interstitial edema increases diffusion distance. What happens to tissue oxygenation?
a) No change
b) Increased oxygenation
c) Decreased tissue oxygenation
d) Only CO₂ affected
Explanation: Interstitial edema increases diffusion distance between capillary and cells, reducing oxygen delivery and impairing CO₂ removal; tissues may become hypoxic despite normal arterial oxygen content. Severe edema in lungs causes impaired gas exchange and hypoxemia. Clinically, pulmonary edema reduces arterial PO₂. Answer: c) Decreased tissue oxygenation, especially during exertion episodes.
4) Which gas diffuses faster across biological membranes?
a) Carbon dioxide
b) Oxygen
c) Nitrogen
d) Helium
Explanation: Carbon dioxide diffuses approximately 20 times faster than oxygen across biological membranes because of higher solubility despite lower gradient; CO₂'s greater diffusion coefficient allows rapid removal from tissues though O₂ transport remains diffusion-limited. Clinically, CO₂ clearance often preserved when oxygenation fails. Answer: a) Carbon dioxide in many disease states too.
5) Typical systemic arterial PO₂ that provides driving force for tissue diffusion is approximately?
a) 40 mmHg
b) 100 mmHg
c) 250 mmHg
d) 760 mmHg
Explanation: Normal systemic arterial PO₂ is about 100 mmHg, creating a substantial gradient versus tissue PO₂ (~40 mmHg) that drives diffusion. Lowered arterial PO₂ reduces this gradient and compromises oxygen delivery, leading to tissue hypoxia if severe. Answer: b) Arterial PO₂ ≈ 100 mmHg, commonly measured by arterial blood gas analysis.
6) In anemia, how is tissue oxygen delivery affected despite normal PaO₂?
a) Unchanged oxygen content
b) Increased oxygen content
c) Reduced oxygen content despite normal PaO₂
d) PaO₂ falls dramatically
Explanation: In anemia arterial oxygen content falls due to reduced hemoglobin concentration despite normal saturation and PO₂; tissues compensate by increasing cardiac output and extracting more oxygen, but severe anemia produces tissue hypoxia even with normal gas exchange. Transfusion raises oxygen content. Answer: c) Reduced oxygen content despite normal PaO₂ levels.
7) Which pathology is classically diffusion-limited for O₂ transfer?
a) Pulmonary fibrosis
b) Right-to-left shunt
c) Hypoventilation
d) Anemia
Explanation: Pulmonary fibrosis thickens alveolar-capillary membrane, increasing diffusion distance and causing diffusion limitation especially during exercise when transit time shortens; oxygen uptake is impaired causing hypoxemia and widened A–a gradient. Right-to-left shunt causes hypoxemia but not diffusion limitation mechanism. Answer: a) Pulmonary fibrosis treatment may include oxygen therapy and antifibrotic agents.
8) Exercise increases oxygen exchange by which microvascular change?
a) Decreased diffusion capacity
b) Increased diffusion capacity due to recruitment
c) Reduced capillary surface area
d) Increased diffusion distance
Explanation: During exercise pulmonary and systemic capillary recruitment and increased perfusion elevate overall diffusion capacity for oxygen (DL_O₂), shortening transit time but increasing surface area and partial pressure gradients, thereby enhancing gas exchange. Diffusion capacity measurements rise with workload. Answer: b) Increased diffusion capacity due to recruitment and higher cardiac output.
9) Diffusion hypoxia is a clinical phenomenon seen when?
a) Nitrous oxide is discontinued
b) Patient breathes 100% oxygen for prolonged period
c) During carbon monoxide poisoning
d) With severe anemia only
Explanation: Diffusion hypoxia occurs when nitrous oxide is discontinued; rapid efflux of N₂O from blood into alveoli dilutes alveolar oxygen and may transiently lower its partial pressure, causing hypoxia if supplemental oxygen not provided. This is a clinical example of diffusion phenomenon. Answer: a) After nitrous oxide discontinuation during emergence recovery.
10) Why are venules not primary sites for gas exchange?
a) They have maximal exchange
b) They have thin walls like capillaries
c) They are upstream of capillaries
d) Venules are not primary exchange sites
Explanation: Venules and veins have thicker walls, lower surface area, and are located downstream where diffusion gradients are reduced; primary gas exchange occurs across capillary endothelium with minimal exchange at venules. Venules specialize in fluid and leukocyte trafficking rather than gas diffusion. Answer: d) Venules are not primary exchange sites clinically.
Keywords (for all questions)
Hering–Breuer reflex: Vagal afferent–mediated inflation reflex that terminates inspiration and prolongs expiration.
Pulmonary stretch receptors (PSR): Slowly adapting receptors in airway smooth muscle activated by lung inflation.
J receptors (juxtacapillary): C-fiber endings in alveolar walls; stimulated by interstitial edema; cause rapid, shallow breathing.
Deflation reflex: Lung deflation triggers increased inspiratory effort via vagal afferents.
Vagotomy: Cutting vagus abolishes Hering–Breuer reflex; tends to produce slow, deep breaths.
Apneustic center: Pontine area that promotes prolonged inspiration; normally inhibited by vagal input and pneumotaxic center.
Pneumotaxic center: Pontine center limiting inspiration, regulating rate and pattern.
Compliance: Change in lung volume per unit pressure; higher compliance augments PSR activation at a given pressure.
Tidal volume (VT): Volume of air inhaled or exhaled per normal breath (~500 mL adult).
PEEP: Positive end-expiratory pressure; affects lung volume, PSR firing, and reflexes during ventilation.
Central chemoreceptors: Sense CSF pH/PaCO₂; drive ventilation independent of PSR.
Peripheral chemoreceptors: Carotid/aortic bodies sensing PaO₂, PaCO₂, pH; mediate hypoxic drive.
Chapter: Respiratory Physiology | Topic: Neural Control of Breathing | Subtopic: Hering–Breuer Reflex
Lead Question – 2012
Herring Breuer reflex is an increase in ?
a) Duration of inspiration
b) Duration of expiration
c) Depth of inspiration
d) Depth of expiration
Explanation: The Hering–Breuer inflation reflex, mediated by slowly adapting pulmonary stretch receptors via the vagus, terminates inspiration to prevent overinflation, thereby prolonging expiratory time. This reflex is prominent at larger tidal volumes (e.g., exercise or mechanical ventilation) and is abolished by vagotomy. Answer: b) Duration of expiration.
1) In a ventilated ICU patient with high VT, activation of pulmonary stretch receptors will most likely:
a) Increase inspiratory time b) Prolong expiratory time c) Cause apnea via chemoreceptors d) Reduce vagal tone
Explanation: Large tidal volumes increase PSR firing, engaging the Hering–Breuer inflation reflex that ends inspiration and prolongs expiration, reducing respiratory rate. Chemoreceptors are not the primary mediators here; vagal afferents are. Answer: b) Prolong expiratory time.
2) Which nerve carries afferents essential for the Hering–Breuer inflation reflex?
a) Glossopharyngeal b) Vagus c) Phrenic d) Intercostal
Explanation: Slowly adapting pulmonary stretch receptors send impulses via the vagus to medullary respiratory centers. Vagotomy abolishes the reflex and leads to slower, deeper breathing patterns due to loss of inspiratory termination. Answer: b) Vagus.
3) A neonate’s breathing pattern is strongly influenced by the Hering–Breuer reflex. The primary functional benefit is:
a) Enhancing hypoxic drive b) Preventing alveolar overdistension c) Increasing dead space d) Facilitating CO₂ retention
Explanation: In neonates, the Hering–Breuer reflex is more prominent and helps terminate inspiration to avoid overdistension of compliant lungs, stabilizing VT and FRC. It does not increase dead space or promote CO₂ retention physiologically. Answer: b) Preventing alveolar overdistension.
4) Following bilateral vagotomy in an animal model, which breathing pattern is expected?
a) Rapid, shallow breathing b) Slow, deep breathing c) Cheyne–Stokes respiration d) Apneustic breathing relieved
Explanation: Loss of vagal afferents removes stretch-mediated inspiratory termination, producing slow, deep breaths. Apneustic patterns arise with pontine lesions, not isolated vagotomy. Rapid shallow breathing reflects J-receptor activity, not PSR loss. Answer: b) Slow, deep breathing.
5) In interstitial pulmonary edema, stimulation of J receptors leads to:
a) Prolonged expiration b) Rapid, shallow breathing c) Increased VT with slower rate d) Apnea followed by hyperpnea
Explanation: J (juxtacapillary) receptors are C-fiber endings sensitive to interstitial fluid; activation triggers tachypnea with low VT (rapid, shallow). This is distinct from PSR-mediated inflation reflex which prolongs expiration. Answer: b) Rapid, shallow breathing.
6) During exercise, why does the Hering–Breuer reflex become more relevant?
a) Higher PaCO₂ sensitizes PSR b) Larger VT increases PSR firing c) Airway resistance falls, silencing PSR d) Peripheral chemoreceptors inhibit PSR
Explanation: Exercise increases tidal volume; lung inflation enhances slowly adapting PSR discharge, aiding appropriate inspiratory termination and expiratory timing at high volumes. Chemoreceptor changes are parallel but not the mechanism for PSR activation. Answer: b) Larger VT increases PSR firing.
7) A patient on high PEEP shows decreased inspiratory time on the ventilator. The best explanation is:
a) Central chemoreceptor suppression b) Increased PSR activation by higher lung volume c) Haldane effect d) Reduced compliance lowering PSR firing
Explanation: PEEP elevates end-expiratory lung volume, increasing PSR activity and promoting earlier inspiratory cutoff (shorter inspiratory time), consistent with the Hering–Breuer effect. Central chemoreceptors and Haldane effect are unrelated. Answer: b) Increased PSR activation by higher lung volume.
8) Which brain region integrates vagal stretch afferents to terminate inspiration?
a) Dorsal respiratory group (DRG) b) Ventral respiratory group (VRG) c) Apneustic center alone d) Cerebellum
Explanation: DRG in the medulla receives vagal afferents from PSR and modulates inspiratory off-switch; pontine pneumotaxic influences also help, but DRG is the key medullary integrator. VRG is more active in forced breathing. Answer: a) Dorsal respiratory group (DRG).
9) In an apneustic animal (pontine lesion), intact vagal afferents would:
a) Worsen apneusis b) Partially relieve prolonged inspiration c) Cause Cheyne–Stokes pattern d) Have no effect
Explanation: Vagal stretch input can partially terminate the prolonged inspiratory “apneustic” pattern by providing an inspiratory off-switch, reducing the severity of breath-holding phases. Answer: b) Partially relieve prolonged inspiration.
10) A COPD patient shows larger VT after bronchodilator. How does this affect the Hering–Breuer reflex?
a) Diminishes reflex due to less stretch b) Augments reflex via greater stretch c) No change expected d) Converts to deflation reflex
Explanation: Improved airflow can increase VT at similar effort, raising lung stretch and PSR firing, thus enhancing the inflation reflex and earlier inspiratory termination. Answer: b) Augments reflex via greater stretch.
11) Which change most directly abolishes the Hering–Breuer inflation reflex?
a) Carotid body denervation b) Vagotomy c) Phrenic neurectomy d) Increased CSF bicarbonate
Explanation: The inflation reflex depends on vagal afferents from pulmonary stretch receptors. Cutting the vagus removes the signal to medullary centers, abolishing inspiratory off-switch. Carotid bodies and CSF buffering affect chemoreception, not PSR afferents. Answer: b) Vagotomy.
Chapter: Respiratory System
Topic: Pulmonary Volumes and Capacities
Subtopic: Vital Capacity
Keyword Definitions:
Tidal Volume (TV) - Air inspired or expired during normal breathing.
Inspiratory Reserve Volume (IRV) - Extra volume of air inhaled after normal inspiration.
Expiratory Reserve Volume (ERV) - Extra air exhaled after normal expiration.
Residual Volume (RV) - Air remaining in lungs after maximal expiration.
Vital Capacity (VC) - Maximum air exhaled after maximum inspiration.
Total Lung Capacity (TLC) - Sum of all lung volumes.
Functional Residual Capacity (FRC) - Air left after normal expiration.
Spirometry - Test to measure lung volumes and capacities (except RV).
Restrictive Lung Disease - Condition with reduced VC due to decreased lung expansion.
Obstructive Lung Disease - Condition with increased RV due to airflow limitation.
Lead Question - 2012
Which of the following defines vital capacity?
a) Air in lung after normal expiration
b) Maximum air that can be expirated after normal inspiration
c) Maximum air that can be expirated after maximum inspiration
d) Maximum air in lung after end of maximal inspiration
Explanation: Vital capacity is defined as the maximum volume of air a person can exhale after a maximal inspiration. It includes tidal volume, inspiratory reserve volume, and expiratory reserve volume but excludes residual volume. The correct answer is c) Maximum air that can be expirated after maximum inspiration.
Guessed Question 1
A 50-year-old smoker undergoes spirometry. His vital capacity is reduced. Likely cause?
a) Emphysema
b) Pulmonary fibrosis
c) Asthma
d) Chronic bronchitis
Explanation: Pulmonary fibrosis restricts lung expansion, lowering vital capacity. In obstructive diseases like asthma and emphysema, VC is relatively preserved, though residual volume increases. Thus, the correct answer is b) Pulmonary fibrosis.
Guessed Question 2
Which lung volume cannot be measured by spirometry?
a) Tidal volume
b) Vital capacity
c) Residual volume
d) Inspiratory reserve volume
Explanation: Spirometry measures all volumes except residual volume, functional residual capacity, and total lung capacity. Residual volume cannot be exhaled and requires helium dilution or body plethysmography. Correct answer: c) Residual volume.
Guessed Question 3
A patient with kyphoscoliosis has reduced vital capacity. The mechanism is?
a) Increased compliance
b) Reduced chest wall expansion
c) Increased residual volume
d) Airway obstruction
Explanation: In kyphoscoliosis, chest wall restriction prevents full lung expansion, reducing vital capacity. It is a restrictive pattern. Correct answer: b) Reduced chest wall expansion.
Guessed Question 4
Which combination of volumes constitutes vital capacity?
a) TV + IRV + ERV
b) TV + IRV + RV
c) IRV + ERV + RV
d) TV + ERV + RV
Explanation: Vital capacity is the sum of tidal volume, inspiratory reserve volume, and expiratory reserve volume. It does not include residual volume. Correct answer: a) TV + IRV + ERV.
Guessed Question 5
Vital capacity is maximum in which position?
a) Supine
b) Standing
c) Sitting
d) Prone
Explanation: Vital capacity is maximum in standing position due to reduced abdominal pressure on diaphragm and maximum lung expansion. It decreases in supine due to abdominal viscera pushing the diaphragm upwards. Correct answer: b) Standing.
Guessed Question 6
A patient with severe COPD shows increased total lung capacity but decreased vital capacity. Cause?
a) Increased IRV
b) Increased RV
c) Reduced TV
d) Reduced ERV
Explanation: In COPD, air trapping leads to increased residual volume, which decreases vital capacity despite increased TLC. Correct answer: b) Increased RV.
Guessed Question 7
A medical student performs spirometry. FVC = 3L, FEV1 = 2.7L. Interpretation?
a) Normal lung function
b) Obstructive disease
c) Restrictive disease
d) Mixed disorder
Explanation: FEV1/FVC ratio = 2.7/3 = 90% (normal >80%), with reduced FVC. This suggests restrictive lung disease where vital capacity is reduced. Correct answer: c) Restrictive disease.
Guessed Question 8
In an athlete, which factor contributes to increased vital capacity?
a) Decreased residual volume
b) Stronger respiratory muscles
c) Reduced total lung capacity
d) Decreased tidal volume
Explanation: Athletes have stronger respiratory muscles and better lung expansion, leading to increased vital capacity. Correct answer: b) Stronger respiratory muscles.
Guessed Question 9
A patient has TLC = 6L, RV = 2L. What is the vital capacity?
a) 2L
b) 4L
c) 6L
d) 8L
Explanation: Vital capacity = TLC – RV = 6 – 2 = 4L. Correct answer: b) 4L.
Guessed Question 10
A 70-year-old man shows age-related changes in lung volumes. Which is true?
a) VC increases
b) RV decreases
c) VC decreases
d) TLC decreases
Explanation: With aging, lung compliance increases, residual volume increases, and vital capacity decreases due to weaker respiratory muscles. Total lung capacity remains nearly constant. Correct answer: c) VC decreases.
Chapter: Respiratory System
Topic: Pulmonary Physiology
Subtopic: Alveolar Stability
Keyword Definitions:
Alveoli - Tiny air sacs in lungs where gas exchange occurs.
Surfactant - Substance secreted by type II pneumocytes that reduces surface tension in alveoli.
Residual Volume - Amount of air left in lungs after maximal expiration.
Lung Compliance - Measure of lung’s ability to expand.
Intrapleural Pressure - Negative pressure within pleural cavity that prevents lung collapse.
Surface Tension - Force at the liquid-air interface tending to collapse alveoli.
Type II Pneumocytes - Alveolar cells producing surfactant.
Atelectasis - Collapse of alveoli due to lack of surfactant or obstruction.
Lead Question - 2012
Stability of alveoli is maintained by?
a) Lung compliance
b) Negative intrapleural pressure
c) Increase in alveolar surface area by the surfactant
d) Residual air in alveoli
Explanation: Alveolar stability is primarily maintained by surfactant, which reduces surface tension, preventing collapse of smaller alveoli into larger ones. Compliance and intrapleural pressure support lung expansion, but surfactant directly stabilizes alveoli. Thus, the correct answer is c) Increase in alveolar surface area by the surfactant.
Guessed Question 1
Newborn with respiratory distress likely has deficiency of?
a) Type I pneumocytes
b) Type II pneumocytes
c) Macrophages
d) Ciliated cells
Explanation: Neonatal respiratory distress syndrome is due to deficiency of surfactant, secreted by type II pneumocytes. This leads to alveolar collapse and hypoxemia. Hence the correct answer is b) Type II pneumocytes.
Guessed Question 2
A 45-year-old smoker develops recurrent alveolar collapse. Which factor is most impaired?
a) Residual volume
b) Surfactant secretion
c) Intrapleural pressure
d) Lung compliance
Explanation: Smoking reduces surfactant production and damages alveolar walls. Lack of surfactant increases surface tension, leading to alveolar instability. The correct answer is b) Surfactant secretion.
Guessed Question 3
In premature infants, alveolar collapse is due to?
a) Increased intrapleural pressure
b) Surfactant deficiency
c) Increased lung compliance
d) Increased residual volume
Explanation: Premature infants (b) Surfactant deficiency.
Guessed Question 4
Which law explains tendency of alveoli to collapse without surfactant?
a) Poiseuille’s law
b) Boyle’s law
c) Laplace’s law
d) Dalton’s law
Explanation: Laplace’s law states pressure within alveoli is directly proportional to surface tension and inversely proportional to radius. Without surfactant, small alveoli collapse. Correct answer: c) Laplace’s law.
Guessed Question 5
Which condition leads to increased surfactant production?
a) Prolonged bed rest
b) Glucocorticoid administration
c) Hypercapnia
d) Hypothermia
Explanation: Corticosteroids stimulate surfactant production, hence are given antenatally to mothers at risk of preterm delivery. Correct answer: b) Glucocorticoid administration.
Guessed Question 6
Surfactant secretion starts at which fetal week?
a) 12 weeks
b) 20 weeks
c) 24 weeks
d) 34 weeks
Explanation: Surfactant production begins at 24 weeks and reaches sufficient levels for alveolar stability by 34–36 weeks of gestation. Correct answer: c) 24 weeks.
Guessed Question 7
A patient with ARDS develops alveolar collapse. Mechanism?
a) Increased compliance
b) Loss of surfactant
c) Increased intrapleural negativity
d) Increased residual air
Explanation: ARDS leads to diffuse alveolar damage and surfactant dysfunction, causing alveolar collapse and impaired gas exchange. Correct answer: b) Loss of surfactant.
Guessed Question 8
Which component of surfactant is most important?
a) Sphingomyelin
b) Lecithin (Dipalmitoylphosphatidylcholine)
c) Cholesterol
d) Glycolipids
Explanation: The major active component of surfactant is lecithin (DPPC), which lowers alveolar surface tension and maintains alveolar stability. Correct answer: b) Lecithin (DPPC).
Guessed Question 9
Which test estimates fetal lung maturity?
a) Lecithin-sphingomyelin ratio
b) Amniotic fluid bilirubin
c) Amniotic fluid creatinine
d) Fetal hemoglobin
Explanation: Lecithin-sphingomyelin (L/S) ratio in amniotic fluid indicates fetal lung maturity. Ratio ≥2 suggests adequate surfactant and alveolar stability. Correct answer: a) Lecithin-sphingomyelin ratio.
Guessed Question 10
Which alveolar cell is responsible for surfactant recycling?
a) Type I pneumocyte
b) Type II pneumocyte
c) Macrophage
d) Endothelial cell
Explanation: Type II pneumocytes both secrete and recycle surfactant, ensuring continuous maintenance of alveolar stability. Correct answer: b) Type II pneumocyte.
Keyword Definitions
Compliance - Change in lung volume per unit change in transpulmonary pressure (ΔV/ΔP).
Surfactant - Surface-active lipoprotein from type II pneumocytes that lowers alveolar surface tension.
Elastance - Reciprocal of compliance; tendency of lung to recoil.
Static compliance - Compliance measured with no airflow (plateau conditions).
Dynamic compliance - Compliance measured during active airflow, includes resistance effects.
FRC (Functional residual capacity) - Lung volume at end-normal expiration where elastic forces balance.
Emphysema - Destructive airspace disease increasing lung compliance and reducing elastic recoil.
Fibrosis - Interstitial scarring that reduces lung compliance and increases elastic recoil.
Esophageal pressure - Clinical surrogate for pleural pressure used to estimate transpulmonary pressure.
Surface tension - Liquid film force at air–liquid interface that reduces lung compliance if high.
Chapter: Respiratory Mechanics Topic: Lung Compliance Subtopic: Determinants and Clinical Changes
Lead Question – 2012
True statement relating to compliance of lung:
a) Increased by surfactant
b) Decreased in emphysema
c) At height of inspiration compliance is less
d) It can be measured by measuring intrapleural pressure at different lung volume
e) None
Explanation: Surfactant lowers alveolar surface tension, increasing compliance and easing inflation; hence (a) is true. Emphysema increases, not decreases, compliance. Compliance falls at high lung volumes and can be measured using intrapleural (esophageal) pressure changes—so (a) is the best single true statement. Answer: a)
1) Which condition most decreases lung compliance?
a) Pulmonary fibrosis
b) Emphysema
c) Surfactant excess
d) Increased 2,3-BPG
Explanation: Pulmonary fibrosis causes stiff, scarred lungs with reduced compliance, increasing elastic recoil and work of breathing. Fibrosis limits volume change for any transpulmonary pressure increment and causes restrictive physiology. Thus a) Pulmonary fibrosis is correct and clinically presents with low lung volumes and high elastic work during inspiration.
2) Dynamic compliance differs from static compliance because dynamic includes effects of:
a) Airway resistance during flow
b) Surface tension only
c) Blood volume changes
d) Plateaus at zero flow
Explanation: Dynamic compliance measured during active airflow incorporates airway resistance and viscous losses, unlike static compliance measured at zero flow. Increased resistance (eg, bronchospasm) lowers dynamic but not static compliance. Therefore a) Airway resistance during flow is correct; clinicians note differences when assessing ventilated patients.
3) Clinically, which bedside measurement best estimates static lung compliance in an intubated patient?
a) Tidal volume / (Plateau pressure − PEEP)
b) Peak pressure / tidal volume
c) RR × tidal volume
d) PEEP alone
Explanation: Static compliance equals tidal volume divided by (plateau pressure minus PEEP) measured during an inspiratory hold. This isolates elastic properties by eliminating flow-related resistive pressure. Thus a) is correct and commonly used to guide ventilator settings to minimize volutrauma in ARDS and other conditions.
4) In emphysema, which pattern is expected?
a) Increased compliance, reduced recoil
b) Decreased compliance, increased recoil
c) Normal compliance, increased surface tension
d) Reduced compliance, reduced dead space
Explanation: Emphysema destroys alveolar walls and elastin, increasing lung compliance and reducing elastic recoil, promoting air trapping and increased residual volume. Therefore a) Increased compliance, reduced recoil is correct and explains floppy lungs, expiratory flow limitation, and dynamic hyperinflation clinically.
5) Which factor most increases lung compliance?
a) Higher surfactant concentration
b) Interstitial fibrosis
c) Pulmonary edema
d) Atelectasis
Explanation: Surfactant lowers surface tension and increases compliance, easing alveolar expansion. Conditions like fibrosis, edema, and atelectasis increase stiffness or surface tension, reducing compliance. Thus a) Higher surfactant concentration is correct and is physiologically crucial in neonates and lung injury management.
6) Why does compliance fall at very high lung volumes?
a) Elastic fibers reach their limit and stiffen
b) Surfactant concentration rises excessively
c) Airway resistance vanishes
d) Blood volume increases
Explanation: At high volumes, elastin and collagen fibers are stretched near their limits, requiring larger pressure changes per volume increment, so compliance falls. Thus a) Elastic fibers reach their limit and stiffen is correct. This explains the flattening of the pressure–volume curve at end-inspiration clinically.
7) Measuring compliance using intrapleural (esophageal) pressure is important because:
a) It estimates true transpulmonary pressure
b) It directly measures alveolar surface tension
c) It replaces arterial blood gas analysis
d) It determines bronchial tone
Explanation: Esophageal pressure approximates pleural pressure, allowing calculation of transpulmonary pressure (alveolar minus pleural) and thus true lung compliance. This distinction separates chest wall from lung mechanics and guides PEEP titration in ventilated patients. Therefore a) is correct and clinically useful in complex respiratory failure.
8) In acute pulmonary edema compliance usually:
a) Decreases because interstitial fluid increases stiffness
b) Increases because fluid lubricates alveoli
c) Remains unchanged
d) Is irrelevant clinically
Explanation: Interstitial and alveolar fluid increases tissue stiffness and surface tension effects, reducing lung compliance and increasing work of breathing. Therefore a) Decreases is correct. Clinicians see reduced tidal volumes and difficulty ventilating; treating edema can improve compliance rapidly.
9) Which neonatal condition has very low lung compliance?
a) Neonatal respiratory distress syndrome (surfactant deficiency)
b) Transient tachypnea of newborn
c) Meconium aspiration with hypercompliance
d) Patent ductus arteriosus
Explanation: Neonatal RDS features surfactant deficiency, high alveolar surface tension, collapse, and markedly reduced compliance. This produces stiff lungs, low volumes, and severe respiratory distress; surfactant replacement raises compliance. Thus a) is correct and is a cornerstone of neonatal respiratory management.
10) Which ventilator change increases measured static compliance if lung recruitment occurs?
a) Apply optimal PEEP to recruit alveoli
b) Increase delivered flow rate
c) Decrease inspiratory time only
d) Increase circuit resistance
Explanation: Optimal PEEP opens collapsed alveoli, increasing available volume for a given pressure and therefore raising measured static compliance. Recruitment reduces atelectasis and improves compliance; increasing flow or resistance affects dynamic measures, not static compliance. Hence, a) is correct and used in ARDS ventilation strategies.
Keyword Definitions
Bohr effect - Rightward shift of O₂–Hb curve with increased H⁺ or CO₂, aiding O₂ unloading.
Haldane effect - Hemoglobin's reduced CO₂ affinity when oxygenated, promoting CO₂ uptake in tissues.
Oxygen affinity - How tightly haemoglobin binds O₂; influenced by pH, CO₂, temperature, 2,3-BPG.
2,3-BPG - Red cell metabolite that lowers hemoglobin O₂ affinity, shifting the curve rightward.
Right shift - Decreased O₂ affinity; facilitates O₂ release to tissues.
Left shift - Increased O₂ affinity; hemoglobin holds O₂ more tightly.
PaO₂ - Arterial O₂ partial pressure; main stimulus for peripheral chemoreceptors when low.
SaO₂ - Hemoglobin oxygen saturation.
Carboxyhemoglobin - CO bound to Hb, raises apparent SaO₂ but prevents O₂ delivery.
Pulse oximetry - Noninvasive saturation monitor; cannot distinguish dyshemoglobinemias reliably.
Chapter: Respiratory Physiology Topic: Hemoglobin & Gas Transport Subtopic: Bohr and Haldane Effects
Lead Question – 2012
Bohr effect is described as: (also September 2009)
a) Decrease in CO2 affinity of hemoglobin when the pH of blood rises
b) Decrease in CO2 affinity of hemoglobin when the pH of blood falls
c) Decrease in O2 affinity of hemoglobin when the pH of blood rises
d) Decrease in O2 affinity of hemoglobin when the pH of blood falls
Explanation: Bohr effect denotes decreased oxygen affinity of hemoglobin when blood pH falls because increased H⁺ and CO₂ stabilize deoxygenated hemoglobin, shifting the curve rightward and enhancing oxygen unloading in metabolically active tissues. Therefore, the correct choice is d) Decrease in O2 affinity of hemoglobin when the pH of blood falls.
1) Which factor shifts the O₂–Hb dissociation curve to the right (facilitating O₂ release)?
a) Increase in pH (alkalosis)
b) Decrease in temperature
c) Increase in 2,3-BPG
d) Fetal hemoglobin presence
Explanation: Increased 2,3-BPG lowers hemoglobin O₂ affinity and shifts the curve right, promoting oxygen unloading in peripheral tissues. Clinically elevated in chronic hypoxia and anemia. Thus answer c) Increase in 2,3-BPG is correct because it decreases O₂ affinity, aiding delivery to metabolically active tissues.
2) A patient with carbon monoxide poisoning will have which effect on oxygen delivery?
a) Increased O₂ unloading to tissues
b) Left shift of O₂–Hb curve and impaired delivery
c) No change in O₂ content
d) Increased PaO₂ compensates
Explanation: Carbon monoxide binds hemoglobin tightly producing carboxyhemoglobin, causing a left shift and increased affinity of remaining sites for O₂, thereby impairing tissue delivery despite normal PaO₂. Clinically, answer b) Left shift of O₂–Hb curve and impaired delivery is correct; oxygen therapy and hyperbaric oxygen are treatments.
3) Which change best explains increased O₂ unloading during fever?
a) Decreased metabolic demand
b) Decreased temperature
c) Right shift from increased temperature
d) Lowered 2,3-BPG
Explanation: Fever raises tissue temperature which shifts the oxyhemoglobin dissociation curve to the right, decreasing O₂ affinity and enhancing unloading. Therefore c) Right shift from increased temperature is correct. Clinically during infection or exercise, this effect supports increased tissue oxygenation to meet metabolic needs.
4) The Haldane effect describes:
a) CO₂ loading when hemoglobin is oxygenated
b) Increased CO₂ carriage when hemoglobin is deoxygenated
c) O₂ binding increased by high CO₂
d) 2,3-BPG reduction with hypoxia
Explanation: The Haldane effect describes how deoxygenated hemoglobin carries more CO₂ and H⁺, facilitating CO₂ uptake in tissues and release in the lungs. Thus answer b) Increased CO₂ carriage when hemoglobin is deoxygenated is correct and explains reciprocal effects of O₂ and CO₂ carriage by hemoglobin in gas exchange physiology.
5) In chronic hypoxia (eg, COPD), which adaptation increases oxygen unloading to tissues?
a) Decreased 2,3-BPG
b) Increased 2,3-BPG
c) Elevated fetal hemoglobin
d) Reduced cardiac output
Explanation: Chronic hypoxia elevates erythrocyte 2,3-BPG levels, which lowers hemoglobin’s O₂ affinity and shifts the dissociation curve right, improving tissue oxygen delivery. Therefore b) Increased 2,3-BPG is correct. This cellular adaptation helps compensate for low arterial oxygen tensions in long-standing hypoxic states.
6) A left shift of the O₂–Hb curve occurs with:
a) Acidosis and fever
b) Increased 2,3-BPG
c) Hypothermia and decreased 2,3-BPG
d) High PCO₂
Explanation: Hypothermia and decreased 2,3-BPG raise hemoglobin affinity for O₂, shifting the curve left and reducing tissue unloading. Thus c) Hypothermia and decreased 2,3-BPG is correct. Clinically this explains reduced peripheral O₂ release in hypothermic patients and influences transfusion and oxygen strategies.
7) Which clinical condition most clearly demonstrates the Bohr effect in action?
a) Tissue hypoperfusion with alkalosis
b) Active exercising muscle with acidosis
c) Hyperventilation causing alkalosis
d) Hypothermia during surgery
Explanation: Exercising muscle produces CO₂ and H⁺ causing local acidosis that decreases Hb O₂ affinity and facilitates unloading; this is the Bohr effect. Therefore answer b) Active exercising muscle with acidosis is correct and clinically explains improved oxygen delivery to exercising tissues via rightward curve shift.
8) Which statement regarding fetal hemoglobin (HbF) is true?
a) HbF has higher 2,3-BPG binding than adult Hb
b) HbF shifts the O₂–Hb curve to the right
c) HbF has higher O₂ affinity than adult HbA
d) HbF increases CO₂ unloading in placenta
Explanation: Fetal hemoglobin binds 2,3-BPG less avidly, giving it higher O₂ affinity and a left-shifted dissociation curve relative to adult HbA, facilitating placental oxygen transfer. Thus c) HbF has higher O₂ affinity than adult HbA is correct and underlies fetal oxygen extraction from maternal blood.
9) Which lab finding would you expect with increased peripheral tissue O₂ unloading?
a) Decreased venous PCO₂
b) Increased venous O₂ saturation (SvO₂)
c) Increased arteriovenous O₂ difference
d) Decreased lactate in tissues
Explanation: Enhanced O₂ unloading lowers venous O₂ content and saturation, increasing the arteriovenous O₂ difference. Clinically a larger a-v O₂ difference (arterial minus venous O₂ content) reflects greater tissue extraction. Therefore c) Increased arteriovenous O₂ difference is the correct answer in states of high extraction.
10) A patient with sepsis is vasodilated and hypermetabolic. Which combination alters O₂ delivery and promotes Bohr effect unloading?
a) Alkalosis, hypothermia
b) Acidosis, hyperthermia
c) Decreased 2,3-BPG, left shift
d) Reduced CO₂ production
Explanation: Sepsis often produces acidosis and fever which decrease hemoglobin O₂ affinity via the Bohr effect and increased temperature, shifting the dissociation curve right and promoting tissue unloading. Thus answer b) Acidosis, hyperthermia is correct and explains increased peripheral oxygen availability despite systemic illness.
Keywords
Alveolar Ventilation - The amount of fresh air reaching the alveoli per minute.
Respiratory Quotient (RQ) - Ratio of CO2 produced to O2 consumed.
Dead Space - Portion of tidal volume not participating in gas exchange.
Diffusion Capacity - Ability of the lungs to transfer gas from alveoli to blood.
Oxygen Consumption (VO2) - The rate at which oxygen is used by tissues.
Carbon Dioxide Output (VCO2) - Rate at which CO2 is produced and eliminated.
Fick Principle - Relation between blood flow, O2 consumption, and arteriovenous O2 difference.
Arterial Blood Gas (ABG) - Test measuring oxygenation, ventilation, and acid-base balance.
Partial Pressure - Pressure exerted by an individual gas in a mixture.
Minute Ventilation - Total volume of air entering lungs per minute.
Alveolar Gas Equation - Formula to calculate alveolar oxygen pressure (PAO2).
Chapter: Respiratory Physiology
Topic: Pulmonary Ventilation
Subtopic: Oxygen Consumption and Carbon Dioxide Elimination
Lead Question - 2012
Difference in the amount of O2 inspired and CO2 expired?
a) 20 ml/min
b) 50 ml/min
c) 75 ml/min
d) 100 ml/min
Explanation: The average O2 consumption at rest is about 250 ml/min while CO2 output is ~200 ml/min, leaving a difference of 50 ml/min. This reflects tissue O2 utilization exceeding CO2 production. Answer: b) 50 ml/min
Q2. A patient with COPD has a resting VO2 of 300 ml/min and VCO2 of 250 ml/min. The difference between inspired O2 and expired CO2 is?
a) 30 ml/min
b) 40 ml/min
c) 50 ml/min
d) 60 ml/min
Explanation: Here, the difference is 300 - 250 = 50 ml/min. This matches normal physiology, showing metabolic balance despite disease. Answer: c) 50 ml/min
Q3. Normal oxygen consumption in an adult at rest is approximately?
a) 150 ml/min
b) 200 ml/min
c) 250 ml/min
d) 300 ml/min
Explanation: At rest, adults consume ~250 ml/min of O2. This value varies with body size, temperature, and metabolic activity. Answer: c) 250 ml/min
Q4. Carbon dioxide production in a healthy resting adult is?
a) 100 ml/min
b) 150 ml/min
c) 200 ml/min
d) 250 ml/min
Explanation: At rest, CO2 elimination averages 200 ml/min, closely linked to tissue metabolism. Answer: c) 200 ml/min
Q5. Which principle is used to calculate oxygen consumption in physiology labs?
a) Boyle’s law
b) Fick’s principle
c) Dalton’s law
d) Henry’s law
Explanation: Fick’s principle relates blood flow to O2 consumption and the arteriovenous O2 difference. Answer: b) Fick’s principle
Q6. In exercise, oxygen consumption may increase up to?
a) 500 ml/min
b) 1000 ml/min
c) 2000 ml/min
d) 4000 ml/min
Explanation: During heavy exercise, VO2 can reach 4000 ml/min or higher, reflecting increased metabolic demand. Answer: d) 4000 ml/min
Q7. A patient has O2 consumption of 270 ml/min and CO2 production of 220 ml/min. What is the respiratory quotient (RQ)?
a) 0.6
b) 0.7
c) 0.8
d) 1.0
Explanation: RQ = VCO2/VO2 = 220/270 ≈ 0.8, which is normal for a mixed diet. Answer: c) 0.8
Q8. If a patient is on pure carbohydrate diet, the expected RQ is?
a) 0.6
b) 0.7
c) 0.8
d) 1.0
Explanation: Carbohydrate metabolism yields equal O2 consumption and CO2 production, making RQ = 1.0. Answer: d) 1.0
Q9. Which factor increases oxygen consumption significantly?
a) Hypothermia
b) Sepsis
c) Sedation
d) Hypothyroidism
Explanation: Sepsis increases metabolic rate and tissue oxygen use, raising VO2. Answer: b) Sepsis
Q10. Which condition decreases carbon dioxide production?
a) Fever
b) Hyperthyroidism
c) Sedation
d) Exercise
Explanation: Sedation lowers metabolism, thereby reducing CO2 output. Answer: c) Sedation
Q11. During high-altitude hypoxia, which change occurs in VO2 and VCO2?
a) Both increase
b) Both decrease
c) VO2 same, VCO2 decreases
d) VO2 increases, VCO2 same
Explanation: At altitude, metabolism may decrease due to hypoxia, lowering both VO2 and VCO2. Answer: b) Both decrease
Keyword Definitions
Transpulmonary pressure (Ptp): Difference between alveolar pressure (PA) and intrapleural pressure (Ppl).
Alveolar (intraalveolar) pressure (PA): Pressure inside alveoli; near 0 cmH2O at no flow.
Intrapleural pressure (Ppl): Pressure in pleural space; normally negative during quiet breathing.
Transairway pressure: Airway opening pressure minus alveolar pressure (Pao − PA); drives airflow.
Transrespiratory pressure: Airway opening pressure minus body surface pressure (Pao − Pbs).
Plateau pressure (Pplat): Alveolar pressure at zero flow during inspiratory hold.
Peak inspiratory pressure (PIP): Highest circuit pressure; includes resistive and elastic components.
Compliance: ΔV/ΔP; ease of lung expansion for a given pressure change.
Elastance: Reciprocal of compliance; tendency to recoil.
Hysteresis: Inflation curve differs from deflation on the pressure–volume loop.
PEEP: Positive end-expiratory pressure; maintains nonnegative end-expiratory Ptp.
CPAP: Continuous positive airway pressure; splints airways, raises end-expiratory Ptp.
Equal pressure point (EPP): Site where airway and pleural pressures are equal during forced expiration.
Dynamic airway compression: Airway narrowing beyond the EPP during forced expiration.
Auto-PEEP: Trapped gas generating intrinsic PEEP at end expiration.
Driving pressure: Pplat − PEEP; surrogate for tidal stress across the respiratory system.
Functional residual capacity (FRC): Lung volume at end-tidal expiration when forces balance.
Pneumothorax: Air in pleural space raising Ppl, reducing Ptp and collapsing lung.
Esophageal pressure: Surrogate for pleural pressure used to estimate Ptp at bedside.
Barotrauma/Volutrauma: Injury from excessive pressures/overdistension due to high Ptp.
Chapter: Respiratory Physiology Topic: Mechanics of Breathing Subtopic: Pulmonary Pressures and Pressure Gradients
Lead Question – 2012
Transpulmonary pressure is the difference between:
a) The bronchus and atmospheric pressure
b) Pressure in alveoli and intrapleural pressure
c) Atmosphere and intrapleural pressure
d) Atmosphere and intraalveolar pressure
Explanation (Answer: b) Pressure in alveoli and intrapleural pressure) Transpulmonary pressure (Ptp) equals alveolar pressure minus intrapleural pressure (P_A − P_pl). It distends alveoli, keeping them open. At functional residual capacity, Ptp balances elastic recoil. During inspiration, Ppl becomes more negative, increasing Ptp and lung volume; expiration reverses this gradient.
1) Which pressure primarily drives airflow through conducting airways during inspiration?
a) Transairway pressure
b) Transpulmonary pressure
c) Transrespiratory pressure
d) Pleural pressure
Explanation (Answer: a) Transairway pressure) Transairway pressure is mouth or airway opening pressure minus alveolar pressure (Pao − PA). It drives flow through conducting airways, unlike transpulmonary pressure, which distends alveoli. During mechanical ventilation, peak inspiratory pressure minus plateau pressure estimates resistive (transairway) component, distinguishing flow resistance from elastic recoil.
2) Which feature of the lung pressure–volume relationship reflects surfactant recruitment and opening pressures?
a) Linear compliance across volumes
b) Zero hysteresis
c) Constant elastance
d) Hysteresis on inflation/deflation
Explanation (Answer: d) Hysteresis on inflation/deflation) The pressure–volume curve shows hysteresis: at a given volume, inflation requires higher transpulmonary pressure than deflation because surfactant recruitment and alveolar opening thresholds differ. This is independent of airway resistance and reflects lung elasticity and surface tension dynamics, explaining recruitment maneuvers and PEEP effects.
3) During quiet inspiration, which immediate change increases transpulmonary pressure?
a) More positive pleural pressure
b) Increased airway resistance
c) More negative pleural pressure
d) Decreased alveolar compliance
Explanation (Answer: c) More negative pleural pressure increases Ptp) Ptp equals PA − Ppl. During inspiration, muscles make pleural pressure more negative. If alveolar pressure falls less, the difference increases, distending alveoli and drawing air inward. When pleural pressure becomes less negative or positive, Ptp drops, promoting expiration or collapse.
4) In a ventilated ARDS patient, which bedside measure most closely estimates alveolar pressure for calculating Ptp?
a) Peak inspiratory pressure
b) Plateau pressure during inspiratory hold
c) Mean airway pressure
d) End-tidal CO₂
Explanation (Answer: b) Alveolar pressure at zero flow approximates) Plateau pressure during an inspiratory hold reflects alveolar pressure at zero flow, so Ptp ≈ Pplat − Ppl (or −esophageal). Peak pressure overestimates elastic stress from resistance. Target transpulmonary pressure: limit end-inspiratory Ptp, and use PEEP to maintain nonnegative end-expiratory Ptp.
5) To minimize atelectrauma in ARDS, which end-expiratory condition is most appropriate?
a) Negative end-expiratory Ptp
b) Zero PEEP
c) Very high end-inspiratory Ptp
d) Equal or positive end-expiratory Ptp
Explanation (Answer: d) Equal or positive end-expiratory Ptp) Preventing collapse requires maintaining alveolar patency with nonnegative end-expiratory transpulmonary pressure using PEEP. Negative end-expiratory Ptp favors derecruitment and atelectrauma. Excessively high Ptp causes overdistension (volutrauma). Clinicians titrate PEEP so end-expiratory Ptp is near zero to positive, improving oxygenation while minimizing injury.
6) A tall, young man develops sudden pleuritic chest pain and dyspnea. Which process most directly abolishes transpulmonary pressure, collapsing the lung?
a) Atelectasis
b) Pleural effusion
c) Pneumothorax
d) Chest wall restriction
Explanation (Answer: c) Pneumothorax) In pneumothorax, intrapleural pressure approaches atmospheric or positive values, collapsing lung because transpulmonary pressure falls toward zero or negative. Atelectasis reduces surface area and compliance but may preserve a negative Ppl. Pleural effusion increases pleural pressure mildly; chest wall restriction reduces total compliance without nullifying Ptp.
7) For a fixed transpulmonary pressure, which change yields the largest increase in lung volume on the P–V curve?
a) Increased compliance
b) Decreased compliance
c) Increased airway resistance
d) Reduced surfactant
Explanation (Answer: a) Increased compliance) For a given transpulmonary pressure, a more compliant lung exhibits greater volume change (ΔV/ΔP). Stiff lungs (low compliance) require higher Ptp to achieve the same volume. Surfactant deficiency, fibrosis, or edema decrease compliance. Emphysema increases compliance but often sacrifices elastic recoil and small-airway tethering markedly.
8) In forced expiration, which intervention moves the equal pressure point distally and reduces dynamic airway collapse?
a) Decreasing lung volume
b) Increasing lung volume with PEEP
c) Increasing airway resistance
d) Adding dead space
Explanation (Answer: b) Equal pressure point dynamics) During forced expiration, pleural pressure rises, compressing airways. Where airway pressure equals pleural pressure—the equal pressure point—dynamic compression begins. Increasing lung volume or Ptp shifts the point peripherally and splints airways via radial traction. Loss of elastic recoil (low Ptp) causes airway collapse.
9) Which expression correctly defines transrespiratory pressure?
a) PA − Ppl
b) Pao − PA
c) Pao − Pbs
d) Ppl − Pbs
Explanation (Answer: d) Transrespiratory pressure) Transrespiratory pressure equals airway opening pressure minus body surface pressure (Pao − Pbs). It represents pressure moving gas between mouth and alveoli. It partitions into transairway (resistive) plus transpulmonary (elastic) components. In spontaneous breathing, Pbs ≈ atmospheric. In mechanical ventilation, Pao is controlled by ventilator.
10) In obstructive sleep apnea, which statement about end-expiratory transpulmonary pressure and CPAP is true?
a) End-expiratory Ptp is strongly positive without CPAP
b) CPAP lowers end-expiratory Ptp below zero
c) End-expiratory Ptp can become negative; CPAP makes it nonnegative
d) CPAP reduces alveolar pressure but increases pleural pressure
Explanation (Answer: c) Negative Ptp at end expiration) Obstructive apnea with chest effort elevates intrapleural pressure negativity but may cause dynamic closure; if alveoli derecruit, end-expiratory Ptp can become negative, predisposing to atelectrauma. CPAP increases airway opening pressure, making end-expiratory Ptp less negative or positive, preventing collapse and improving oxygenation.
Keyword Definitions
Peripheral chemoreceptors: Carotid/aortic bodies sensing low PaO₂, high PaCO₂, and low pH.
Central chemoreceptors: Medullary receptors sensing CSF H⁺ that reflects arterial PaCO₂.
PaO₂ (arterial oxygen tension): Partial pressure of dissolved oxygen in arterial blood.
Oxygen content (CaO₂): Total O₂ carried (mostly on Hb); may be low in anemia despite normal PaO₂.
Hypercapnia: Elevated PaCO₂; strong stimulus to ventilation (central & peripheral).
Hypocapnia: Low PaCO₂; suppresses chemoreceptor drive and ventilation.
Acidemia (low pH): Increases peripheral chemoreceptor firing; central responds after CSF equilibrates.
Low perfusion pressure: Reduced flow to carotid body causing stagnant hypoxia and stimulation.
Glomus (Type I) cell: O₂-sensing cell in carotid body that releases neurotransmitters to CN IX.
CN IX (Glossopharyngeal): Afferent from carotid body to nucleus tractus solitarius.
CN X (Vagus): Afferent from aortic bodies to medulla.
PaO₂ threshold (~60 mmHg): Level below which carotid body firing rises steeply.
Kussmaul breathing: Deep, rapid respirations in severe metabolic acidosis driven by peripheral chemoreceptors.
Hypoxic drive: Increased ventilation due to low PaO₂, prominent in chronic hypercapnia.
V/Q mismatch: Ventilation–perfusion inequality; O₂ can worsen CO₂ retention by reversing HPV.
Anemia: Reduced Hb concentration; lowers CaO₂ with typically normal PaO₂.
Cyanide poisoning: Impaired cellular O₂ use; normal PaO₂ and SaO₂, minimal chemoreceptor stimulus.
Baroreceptors: Pressure sensors; interact with respiration indirectly but are not chemoreceptors.
Alveolar hypoventilation: Inadequate ventilation causing hypercapnia and hypoxemia.
High-altitude acclimatization: Hypoxia stimulates carotid bodies leading to hyperventilation and renal compensation.
Chapter: Respiratory Physiology Topic: Control of Breathing Subtopic: Central and Peripheral Chemoreflexes
Lead Question – 2012
Peripheral and central chemoreceptors may both contribute to the increased ventilation that occurs as a result of which of the following?
a) A decrease in arterial oxygen content
b) A decrease in arterial blood pressure
c) An increase in arterial carbon dioxide tension
d) A decrease in arterial oxygen tension
Explanation (Answer: c) An increase in arterial carbon dioxide tension)
Hypercapnia raises CSF H⁺ stimulating central chemoreceptors and also activates peripheral chemoreceptors, producing robust hyperventilation. Low PaO₂ primarily stimulates peripheral receptors; low CaO₂ (anemia/CO poisoning) minimally affects them; decreased blood pressure stimulates peripheral chemoreceptors but not central ones directly. Hence both pathways are engaged by increased PaCO₂.
1) A 65-year-old with COPD and chronic hypercapnia presents somnolent. Which intervention most rapidly increases his ventilatory drive?
a) Raise FiO₂ to 1.0 immediately
b) Controlled reduction of PaCO₂ via noninvasive ventilation
c) Infuse bicarbonate
d) Administer acetazolamide acutely
Explanation (Answer: b) Controlled reduction of PaCO₂ via noninvasive ventilation)
Noninvasive ventilation lowers PaCO₂, decreasing CSF H⁺ and unloading both central and peripheral chemoreceptors toward normal responsiveness, improving ventilation. Abrupt high FiO₂ risks worsening V/Q mismatch and CO₂ retention. Bicarbonate may worsen intracellular acidosis; acetazolamide is for altitude acclimatization, not acute COPD hypercapnic encephalopathy.
2) The carotid body shows a dramatic rise in discharge when PaO₂ falls below:
a) 90 mmHg
b) 75 mmHg
c) 60 mmHg
d) 50 mmHg
Explanation (Answer: c) 60 mmHg)
Carotid body activation increases nonlinearly with hypoxemia. Below ~60 mmHg PaO₂, glomus cells depolarize strongly, driving ventilatory response. This threshold explains why modest hypoxemia provokes limited response until PaO₂ falls to clinically significant levels, as at altitude or severe lung disease, then ventilation rises steeply.
3) In severe hemorrhagic shock, tachypnea develops partly because chemoreceptors are stimulated by:
a) Elevated CSF bicarbonate
b) Low perfusion pressure at carotid bodies
c) Increased oxyhemoglobin saturation
d) Stretch of pulmonary receptors
Explanation (Answer: b) Low perfusion pressure at carotid bodies)
Reduced carotid body blood flow causes stagnant hypoxia, augmenting glomus cell activity and ventilation. Baroreflexes also interact, but primary chemoreflex stimulus is low perfusion. CSF bicarbonate elevation dampens central drive; oxyhemoglobin saturation is reduced, not increased; stretch receptors modulate tidal volume, not chemostimulation.
4) A healthy free diver hyperventilates before submersion and faints underwater. The mechanism is best explained by:
a) Hypocapnia delaying the CO₂-driven urge to breathe
b) Enhanced hypoxic sensitivity of central chemoreceptors
c) Increased PaO₂ threshold for carotid bodies
d) Reflex laryngospasm from cold water
Explanation (Answer: a) Hypocapnia delaying the CO₂-driven urge to breathe)
Pre-dive hyperventilation reduces PaCO₂, suppressing central and peripheral chemoreceptor drive. Oxygen falls to syncope-inducing levels before CO₂ rises enough to trigger breathing, causing shallow-water blackout. Central chemoreceptors are not hypoxia sensors; carotid body threshold is around 60 mmHg and is not raised by hyperventilation.
5) Which combination most powerfully stimulates ventilation through both central and peripheral pathways?
a) PaCO₂ 55 mmHg and pH 7.25
b) PaO₂ 55 mmHg with PaCO₂ 30 mmHg
c) Severe anemia with PaO₂ 95 mmHg
d) Normal PaCO₂ with metabolic alkalosis
Explanation (Answer: a) PaCO₂ 55 mmHg and pH 7.25)
Elevated PaCO₂ increases CSF H⁺ (central) and arterial H⁺ (peripheral). Concomitant acidemia further drives carotid body firing, producing strong hyperventilation. Hypocapnia (option b) suppresses drive despite hypoxemia. Anemia with normal PaO₂ weakly stimulates carotid bodies. Alkalosis blunts chemoreceptor responsiveness.
6) Which statement about anemia and chemoreception is MOST accurate?
a) Anemia strongly stimulates central chemoreceptors
b) Anemia powerfully activates carotid bodies at normal PaO₂
c) Anemia minimally activates chemoreceptors unless PaO₂ falls
d) Anemia triggers vagal J-receptors to increase ventilation
Explanation (Answer: c) Anemia minimally activates chemoreceptors unless PaO₂ falls)
Chemoreceptors sense PaO₂, PaCO₂, and pH. In isolated anemia, PaO₂ is typically normal though O₂ content is low; carotid body activation is limited. Central chemoreceptors do not detect O₂ content. J-receptors are pulmonary C fibers, not primary chemoreceptors. Hypoxemia is required for strong carotid body activation.
7) A patient with diabetic ketoacidosis exhibits deep, rapid breathing. The initial trigger for this pattern is primarily:
a) Central chemoreceptors sensing immediate CSF acidosis
b) Peripheral chemoreceptors sensing low arterial pH
c) Baroreceptors responding to hypotension
d) Stretch receptors in intercostal muscles
Explanation (Answer: b) Peripheral chemoreceptors sensing low arterial pH)
In metabolic acidosis, blood H⁺ rises quickly, which carotid bodies detect promptly, driving Kussmaul hyperventilation. CSF equilibrates more slowly; central chemoreceptors contribute later. Baroreceptors modulate cardiovascular reflexes, and muscle stretch receptors are not primary drivers of the chemoreflex ventilatory response.
8) Signals from the carotid body reach the medulla via which pathway?
a) Vagus nerve to NTS
b) Glossopharyngeal nerve (Hering’s nerve) to NTS
c) Trigeminal nerve to spinal trigeminal nucleus
d) Hypoglossal nerve to dorsal respiratory group
Explanation (Answer: b) Glossopharyngeal nerve (Hering’s nerve) to NTS)
Carotid body afferents travel in Hering’s nerve, a branch of CN IX, projecting to the nucleus tractus solitarius. Aortic bodies project via the vagus (CN X). CN V and XII are not chemosensory pathways to the respiratory centers. Hence, glossopharyngeal afferents are correct.
9) At high altitude on day 1, a climber hyperventilates. Which change over 48–72 hours sustains ventilation despite falling CSF H⁺?
a) Renal bicarbonate retention
b) Renal bicarbonate excretion
c) Reduced carotid body sensitivity
d) Increased PaCO₂ due to hypoventilation
Explanation (Answer: b) Renal bicarbonate excretion)
Hyperventilation lowers PaCO₂ and CSF H⁺, initially limiting central drive. Kidneys excrete bicarbonate, lowering blood and CSF buffering, allowing continued central responsiveness to low PaCO₂ while hypoxia keeps carotid bodies active. Retaining bicarbonate would blunt ventilation; carotid sensitivity increases, not decreases; PaCO₂ remains low with acclimatization.
10) A 30-year-old with opioid overdose has pinpoint pupils and shallow breathing. Which immediate physiologic effect of naloxone most restores ventilation?
a) Direct stimulation of carotid glomus cells
b) Reversal of μ-receptor depression of brainstem respiratory centers
c) Rapid rise in PaO₂ stimulating central chemoreceptors
d) Activation of pulmonary stretch receptors
Explanation (Answer: b) Reversal of μ-receptor depression of brainstem respiratory centers)
Opioids suppress medullary respiratory neurons and blunt chemoreceptor responsiveness. Naloxone antagonizes μ-receptors, restoring central drive and responsiveness to PaCO₂/PaO₂. Oxygenation alone does not stimulate central chemoreceptors; stretch receptors modulate inflation reflexes. Carotid glomus cells are not directly activated by naloxone.
11) Which change most strongly depresses both central and peripheral chemoreceptor drive?
a) Acute hypercapnia
b) Hypoxemia with PaO₂ 50 mmHg
c) Iatrogenic hypocapnia from overventilation
d) Metabolic acidosis with pH 7.20
Explanation (Answer: c) Iatrogenic hypocapnia from overventilation)
Hypocapnia lowers CSF and arterial H⁺, suppressing medullary and carotid body activity, reducing ventilatory drive. Hypercapnia and acidosis stimulate chemoreceptors; hypoxemia powerfully activates carotid bodies. Thus, excessive ventilation producing low PaCO₂ is the condition that depresses both central and peripheral chemoreceptor-mediated drive.
Keyword Definitions
Peripheral chemoreceptors: Carotid and aortic bodies that sense low PaO₂, high PaCO₂, and low pH.
Central chemoreceptors: Medullary neurons sensitive to H⁺ in CSF, primarily reflecting PaCO₂.
Hypoxia: Decrease in arterial oxygen tension (PaO₂), potent stimulus for carotid bodies below ~60 mmHg.
Hypocapnia: Reduced PaCO₂; depresses chemoreceptor firing and ventilation.
Acidosis: Decreased blood pH; stimulates peripheral chemoreceptors rapidly.
Low perfusion pressure: Reduced blood flow/pressure at chemoreceptors; enhances stimulus (stagnant hypoxia).
Carotid body: Peripheral chemoreceptor at carotid bifurcation; dominant O₂ sensor, CN IX afferent.
Aortic bodies: Peripheral chemoreceptors along aortic arch; CN X afferent.
PaO₂ threshold (~60 mmHg): Point where carotid body firing rises steeply.
Hypoxic drive: Ventilation driven by low PaO₂, especially in chronic hypercapnia.
Anemia/CO poisoning: Low O₂ content with normal PaO₂; weak stimulus to peripheral chemoreceptors.
Oxygen therapy in COPD: Excess O₂ may blunt hypoxic drive and worsen V/Q mismatch.
Metabolic acidosis: Low HCO₃⁻/pH; stimulates ventilation via peripheral chemoreceptors.
Hypercapnia: Elevated PaCO₂; stimulates ventilation (peripheral and central pathways).
Glossopharyngeal nerve (CN IX): Afferent from carotid body to medulla.
Vagus nerve (CN X): Afferent from aortic bodies to medulla.
Type I (glomus) cell: O₂-sensing cell in carotid body releasing neurotransmitters to afferents.
Alveolar hypoventilation: Reduced ventilation causing hypercapnia and hypoxemia.
Stagnant hypoxia: Low tissue O₂ due to poor perfusion despite normal PaO₂.
Cyanide toxicity: Blocks cellular O₂ use; PaO₂ remains normal, weak peripheral chemoreceptor stimulus.
Chapter: Respiratory Physiology Topic: Control of Breathing Subtopic: Peripheral Chemoreceptors
Lead Question – 2012
Which of the following does NOT stimulate peripheral chemoreceptors:
a) Hypoxia
b) Hypocapnia
c) Acidosis
d) Low perfusion pressure
Explanation (Answer: b) Hypocapnia)
Peripheral chemoreceptors (carotid & aortic bodies) are excited by hypoxia (especially PaO₂ < 60 mmHg), acidosis, hypercapnia, and low perfusion pressure. Hypocapnia reduces arterial CO₂ and H⁺, suppressing chemoreceptor discharge and ventilation. Therefore, among the options, hypocapnia does not stimulate peripheral chemoreceptors and is the correct exception.
1) In a 68-year-old with severe COPD and chronic hypercapnia, the major acute ventilatory drive during an exacerbation is most likely from:
a) Central chemoreceptors sensing CSF alkalosis
b) Peripheral chemoreceptors sensing hypoxemia
c) Lung stretch receptors (Hering–Breuer)
d) J-receptors in alveolar walls
Explanation (Answer: b) Peripheral chemoreceptors sensing hypoxemia)
Chronic hypercapnia blunts central chemoreceptor responsiveness. During exacerbations with low PaO₂, carotid bodies dominate the acute ventilatory drive. Correcting PaO₂ cautiously is vital, as excess oxygen can depress hypoxic drive and worsen V/Q mismatch, increasing PaCO₂. Thus, peripheral chemoreceptors sensing hypoxemia are the main stimulus here.
2) The carotid body begins a steep increase in firing when arterial PaO₂ falls below approximately:
a) 90 mmHg
b) 75 mmHg
c) 60 mmHg
d) 40 mmHg
Explanation (Answer: c) 60 mmHg)
Peripheral chemoreceptor response to oxygen tension is nonlinear. Discharge rises modestly until a threshold, then increases steeply once PaO₂ drops below about 60 mmHg. This defends against hypoxemia by increasing ventilation. Hence, 60 mmHg is the clinically important threshold for robust carotid body stimulation and reflex hyperventilation.
3) Which afferent pathway carries signals from the carotid body to the medulla?
a) Vagus nerve (CN X)
b) Glossopharyngeal nerve (CN IX)
c) Trigeminal nerve (CN V)
d) Hypoglossal nerve (CN XII)
Explanation (Answer: b) Glossopharyngeal nerve (CN IX))
The carotid body at the carotid bifurcation sends chemosensory impulses via Hering’s nerve, a branch of the glossopharyngeal nerve (CN IX), to the nucleus tractus solitarius in the medulla. Aortic bodies project through the vagus nerve (CN X). Therefore, CN IX is the correct afferent for carotid body signaling.
4) A patient with profound anemia (Hb 6 g/dL) but normal PaO₂ is least likely to show strong peripheral chemoreceptor activation because:
a) Chemoreceptors sense PaO₂, not O₂ content
b) They are inhibited by low hemoglobin
c) They respond only to pH changes
d) They are saturated by nitric oxide
Explanation (Answer: a) Chemoreceptors sense PaO₂, not O₂ content)
Peripheral chemoreceptors primarily detect arterial oxygen tension (PaO₂), carbon dioxide, and pH. In anemia, PaO₂ may remain normal despite reduced oxygen content, so chemoreceptor stimulation is limited. Clinical hypoxia occurs at the tissue level, but the carotid bodies respond weakly unless PaO₂ itself falls significantly below ~60 mmHg.
5) Following sudden administration of high-flow oxygen to a hypercapnic COPD patient, CO₂ retention may worsen mainly due to:
a) Increased dead-space from V/Q mismatch
b) Enhanced central chemoreceptor sensitivity
c) Activation of stretch receptors
d) Reduced metabolic CO₂ production
Explanation (Answer: a) Increased dead-space from V/Q mismatch)
Supplemental oxygen can reverse hypoxic pulmonary vasoconstriction, increasing perfusion to poorly ventilated alveoli and worsening V/Q mismatch. This elevates dead-space and PaCO₂. Blunting of hypoxic drive also contributes but is not the dominant mechanism. Hence, increased dead-space from V/Q mismatch explains oxygen-induced hypercapnia in susceptible COPD patients.
6) Which statement about central versus peripheral chemoreceptors is MOST accurate?
a) Central chemoreceptors detect blood pH directly
b) Peripheral chemoreceptors do not respond to pH
c) Central chemoreceptors sense CSF H⁺ driven by PaCO₂
d) Peripheral chemoreceptors are insensitive to hypoxia
Explanation (Answer: c) Central chemoreceptors sense CSF H⁺ driven by PaCO₂)
Central chemoreceptors in the medulla respond primarily to H⁺ in CSF, which reflects arterial CO₂ diffusing across the blood–brain barrier. Blood H⁺ changes without CO₂ penetrate slowly, so peripheral chemoreceptors mediate rapid pH responses. Hypoxia strongly stimulates carotid bodies. Thus, central sensing of CSF H⁺ driven by PaCO₂ is correct.
7) In cardiogenic shock with low arterial pressure, ventilation rises partly because carotid bodies are stimulated by:
a) Elevated CSF bicarbonate
b) Low perfusion pressure (stagnant hypoxia)
c) Pulmonary stretch receptor firing
d) Increased oxyhemoglobin content
Explanation (Answer: b) Low perfusion pressure (stagnant hypoxia))
Reduced blood flow through the carotid body decreases oxygen delivery despite potentially normal PaO₂, producing stagnant hypoxia. This enhances glomus-cell neurotransmission to glossopharyngeal afferents, increasing ventilatory drive. Therefore, in shock states, low perfusion pressure itself is a recognized stimulus for peripheral chemoreceptors and augments respiratory effort.
8) A young diver hyperventilates before a breath-hold. Syncope underwater occurs because hypocapnia:
a) Intensifies carotid body firing
b) Delays the urge to breathe by suppressing CO₂ stimulus
c) Increases central chemoreceptor H⁺
d) Lowers PaO₂ threshold to 80 mmHg
Explanation (Answer: b) Delays the urge to breathe by suppressing CO₂ stimulus)
Pre-dive hyperventilation lowers PaCO₂ (hypocapnia), suppressing central and peripheral chemoreceptor drive, delaying the respiratory urge. PaO₂ can fall to hypoxic levels before CO₂ rises enough to trigger breathing, causing shallow-water blackout. Thus, hypocapnia delays warning signals rather than stimulating chemoreceptors, increasing risk of syncope.
9) Which cellular element is the primary O₂-sensing unit in the carotid body?
a) Type I (glomus) cell
b) Type II sustentacular cell
c) Endothelial cell
d) Schwann cell
Explanation (Answer: a) Type I (glomus) cell)
Type I (glomus) cells detect decreases in PaO₂ and acidosis, leading to membrane depolarization, calcium influx, and neurotransmitter release onto afferent fibers of CN IX. Type II cells are supportive. Therefore, the glomus cell is the fundamental O₂-sensing unit triggering peripheral chemoreceptor signaling to the brainstem.
10) In acute metabolic acidosis (e.g., diabetic ketoacidosis), the rapid increase in ventilation is initiated predominantly by:
a) Central chemoreceptors sensitive to CSF H⁺ immediately
b) Peripheral chemoreceptors sensing low arterial pH
c) Stretch receptors in respiratory muscles
d) Aortic baroreceptors
Explanation (Answer: b) Peripheral chemoreceptors sensing low arterial pH)
Blood H⁺ increases rapidly in metabolic acidosis. Because H⁺ crosses the blood–brain barrier slowly, medullary central chemoreceptors respond later. Carotid bodies sense the acidemia promptly and stimulate hyperventilation (Kussmaul breathing), lowering PaCO₂ to compensate. Thus, peripheral chemoreceptors mediate the early ventilatory response in metabolic acidosis.
11) A patient with suspected cyanide poisoning has normal PaO₂ and SaO₂ but tissue hypoxia. Peripheral chemoreceptor stimulation is expected to be:
a) Markedly increased due to blocked cellular respiration
b) Minimal because PaO₂ is normal
c) Driven solely by baroreceptors
d) Maximal via central chemoreceptors
Explanation (Answer: b) Minimal because PaO₂ is normal)
Cyanide prevents cellular O₂ utilization, but arterial PaO₂ and saturation remain normal. Peripheral chemoreceptors sense PaO₂ rather than cellular extraction, so their activation is limited unless hypoxemia, acidosis, or hypercapnia develops. Therefore, despite tissue hypoxia, carotid-body stimulation is relatively minimal when arterial oxygen tension is preserved.
Chapter: Anatomy
Topic: Respiratory System
Subtopic: Surface Anatomy of Lungs
Keywords:
Lower border of lung: Inferior margin of lung seen in surface anatomy, varies with line of reference (midclavicular, midaxillary, paravertebral).
Midaxillary line: Imaginary vertical line through the apex of axilla, useful in thoracic surface markings.
Pleura: Membranous covering of lungs; parietal pleura extends beyond lung border.
LEAD QUESTION - 2012
Q1. Level of lower border of lung at midaxillary line is
a) 6th rib
b) 8th rib
c) 10th rib
d) 12th rib
Explanation: The lower border of the lung at the midaxillary line lies at the 8th rib. In surface anatomy, lung margins end at the 6th rib (midclavicular), 8th rib (midaxillary), and 10th rib (paravertebral). The pleura extends two ribs lower. Hence, correct answer: 8th rib (b).
Q2. The lower border of the pleura at the midaxillary line corresponds to which rib level?
a) 8th rib
b) 10th rib
c) 12th rib
d) 6th rib
Explanation: The pleura extends two ribs below the lung margin. At the midaxillary line, the lung ends at the 8th rib, and the pleura extends till the 10th rib. This difference is clinically important in pleural tap. Answer: 10th rib (b).
Q3. A pleural tap done at midaxillary line should be inserted at which intercostal space to avoid lung injury?
a) 6th intercostal space
b) 8th intercostal space
c) 9th intercostal space
d) 10th intercostal space
Explanation: To avoid puncturing lung tissue, pleural tap is performed below the lung margin but above pleural reflection, usually in the 9th intercostal space at midaxillary line. This ensures fluid aspiration without injuring lung. Correct answer: 9th intercostal space (c).
Q4. At the midclavicular line, the lower border of the lung is at which rib?
a) 4th rib
b) 6th rib
c) 8th rib
d) 10th rib
Explanation: Surface anatomy shows the lung reaches the 6th rib at the midclavicular line. This landmark is important in clinical percussion and auscultation. Correct answer: 6th rib (b).
Q5. At the paravertebral line, the lower border of the lung is located at which rib?
a) 8th rib
b) 10th rib
c) 12th rib
d) 6th rib
Explanation: Posteriorly, the lung border lies at the 10th rib in the paravertebral line. This corresponds to the lower extent of lung tissue seen in imaging and clinical percussion. Answer: 10th rib (b).
Q6. Which rib level does the pleura reach at paravertebral line?
a) 8th rib
b) 10th rib
c) 12th rib
d) 11th rib
Explanation: The pleura extends two ribs below the lung border. Since the lung ends at the 10th rib paravertebrally, the pleura goes down till the 12th rib in the same line. Correct answer: 12th rib (c).
Q7. A patient with pleural effusion requires aspiration at midaxillary line. The safe level is:
a) 6th intercostal space
b) 8th intercostal space
c) 9th intercostal space
d) 11th intercostal space
Explanation: In pleural effusion aspiration, the 9th intercostal space in the midaxillary line is chosen. It lies below the lung but avoids injury to abdominal organs. Correct answer: 9th intercostal space (c).
Q8. Which structure crosses the midaxillary line at the level of the 8th rib?
a) Lower lung border
b) Pleural reflection
c) Diaphragm dome
d) Cardiac notch
Explanation: The lower lung border crosses the 8th rib in the midaxillary line. Pleura is two ribs lower, diaphragm dome is higher, and cardiac notch lies anteriorly. Correct answer: Lower lung border (a).
Q9. During quiet respiration, costodiaphragmatic recess at midaxillary line extends up to:
a) 6th rib
b) 8th rib
c) 10th rib
d) 12th rib
Explanation: The costodiaphragmatic recess is the potential space between lung and pleura. At midaxillary line, lung ends at 8th rib, pleura at 10th rib, so recess lies between them. Correct answer: 10th rib (c).
Q10. A stab wound at the right midaxillary line at the level of the 9th rib during expiration is most likely to injure:
a) Lung parenchyma
b) Pleural cavity
c) Diaphragm
d) Liver
Explanation: At 9th rib midaxillary line, lung ends higher (8th rib), pleura extends till 10th rib. A stab wound at 9th rib pierces pleural cavity without lung injury, potentially involving diaphragm or liver on right side. Correct answer: Pleural cavity (b).
Oblique Fissure: An anatomical groove dividing the upper and lower lobes of both lungs.
Surface Marking: Reference points on the thoracic wall indicating internal structures.
Lungs: Paired respiratory organs in the thoracic cavity for gas exchange.
Ribs and Costal Cartilage: Structures forming the thoracic cage and surface landmarks.
T3 Vertebra: Third thoracic vertebra, used as a posterior reference point.
Clinical Significance: Knowledge of fissure surface markings guides auscultation, percussion, and thoracic procedures.
Chapter: Respiratory Anatomy
Topic: Lobar Anatomy of Lungs
Subtopic: Oblique Fissure Surface Markings
Lead Question 2012: Surface marking of the oblique fissure of the lung include all except:
a) T3
b) 5th rib
c) 7th rib
d) 6th costal cartilage
Answer: a) T3
Explanation: The oblique fissure of the lungs begins posteriorly at the level of T2 vertebra on the right and T3–T4 vertebra on the left, descending anteriorly to the 6th rib midclavicular line. T3 alone is not a consistent surface landmark. Accurate surface marking is crucial for auscultation, thoracentesis, and imaging interpretation.
1. The oblique fissure separates which lobes of the right lung?
a) Upper and middle lobes
b) Upper and lower lobes
c) Middle and lower lobes
d) Upper and accessory lobes
Answer: b) Upper and lower lobes
Explanation: The oblique fissure divides the upper and lower lobes of the right lung. On the left, it separates the upper and lower lobes as well. Understanding fissure anatomy is important in interpreting X-rays, CT scans, and planning surgical procedures.
2. Posteriorly, the oblique fissure of the left lung corresponds to which vertebra?
a) T1
b) T3–T4
c) T5
d) T6
Answer: b) T3–T4
Explanation: The left oblique fissure begins posteriorly around T3–T4 vertebra and slopes downward to the 6th rib anteriorly. Clinically, this helps localize pulmonary lesions and guide thoracic procedures.
3. Anteriorly, the oblique fissure reaches which rib in midclavicular line?
a) 4th rib
b) 5th rib
c) 6th rib
d) 7th rib
Answer: c) 6th rib
Explanation: The oblique fissure extends anteriorly to the 6th rib in the midclavicular line. This landmark is used during percussion and auscultation of lung fields for clinical assessment of lobar pathology.
4. Which fissure is horizontal in the right lung?
a) Oblique
b) Horizontal
c) Accessory
d) None
Answer: b) Horizontal
Explanation: The right lung has a horizontal fissure that separates the upper and middle lobes, in addition to the oblique fissure. This is clinically important during imaging and surgical interventions.
5. Surface marking of horizontal fissure at midaxillary line corresponds to:
a) 4th rib
b) 5th rib
c) 6th rib
d) 7th rib
Answer: b) 5th rib
Explanation: The horizontal fissure passes from the 4th costal cartilage anteriorly to the 5th rib midaxillary line, separating upper and middle lobes of the right lung. Accurate surface marking is key for thoracentesis.
6. The oblique fissure crosses which costal cartilage anteriorly?
a) 4th
b) 5th
c) 6th
d) 7th
Answer: c) 6th
Explanation: The anterior end of the oblique fissure aligns with the 6th rib/costal cartilage in the midclavicular line. This is critical for identifying lobar boundaries in clinical examination and radiography.
7. Which fissure is absent in the left lung?
a) Oblique
b) Horizontal
c) Both
d) Accessory
Answer: b) Horizontal
Explanation: The left lung has no horizontal fissure. It only has an oblique fissure dividing upper and lower lobes. This anatomical difference is important during imaging and surgery.
8. Oblique fissure aids in clinical assessment of:
a) Heart murmurs
b) Lobar pneumonia
c) Diaphragmatic hernia
d) Mediastinal shift
Answer: b) Lobar pneumonia
Explanation: Oblique fissure separates lobes; identification of lobar boundaries helps in diagnosing localized pneumonia or effusions, guiding auscultation, percussion, and imaging interpretation.
9. Posteriorly, the right oblique fissure starts at which vertebra?
a) T2
b) T3
c) T4
d) T5
Answer: b) T3
Explanation: The right oblique fissure starts posteriorly at T3 vertebra and descends to the 6th rib anteriorly. This is a critical surface landmark for thoracic procedures and clinical examination.
10. The oblique fissure crosses which rib at the midaxillary line?
a) 4th
b) 5th
c) 6th
d) 7th
Answer: b) 5th rib
Explanation: At the midaxillary line, the oblique fissure passes approximately along the 5th rib, separating upper and lower lobes. Recognizing this landmark aids in thoracic auscultation and safe needle placement for procedures like pleural tap.
Chapter: Respiratory System Anatomy
Topic: Larynx and Airway Landmarks
Subtopic: Cricoid Cartilage and Related Structures
Keyword Definition
Cricoid cartilage: A complete ring-shaped cartilage located below the thyroid cartilage at the C6 vertebral level, forming part of the larynx.
C6 vertebra: A cervical vertebral level marking anatomical landmarks like the cricoid cartilage and start of trachea and esophagus.
Larynx: Voice box containing vocal cords, located in the neck, functioning in phonation, airway protection, and breathing.
Trachea: Airway tube starting below the larynx at C6 and extending to the carina.
Esophagus: Muscular tube posterior to trachea, beginning at C6 level, conveying food to the stomach.
Thyroid cartilage: Largest laryngeal cartilage forming the laryngeal prominence or Adam's apple.
Recurrent laryngeal nerve: Branch of vagus nerve supplying motor function to all intrinsic laryngeal muscles except cricothyroid.
Emergency cricothyrotomy: A lifesaving airway procedure performed through the cricothyroid membrane.
Pharynx: Musculomembranous tube connecting nasal and oral cavities to the larynx and esophagus.
Laryngopharynx: Lowest part of the pharynx, extending from the hyoid bone to the cricoid cartilage.
Lead Question - 2012:
Cricoid cartilage lies at which vertebral level?
a) C3
b) C6
c) T1
d) T4
The correct answer is C6. The cricoid cartilage marks the junction of the larynx and trachea anteriorly and the beginning of the esophagus posteriorly. This landmark is vital in clinical medicine for procedures like cricothyrotomy and intubation. It also correlates with the lower border of the pharynx and entry of the recurrent laryngeal nerves into the larynx.
1. Which structure lies directly posterior to the cricoid cartilage?
a) Trachea
b) Esophagus
c) Thyroid gland
d) Vertebral artery
Answer: Esophagus. The esophagus begins at the level of the cricoid cartilage (C6) and lies directly behind it. This relationship is critical in endoscopy, nasogastric tube insertion, and esophageal surgeries.
2. During emergency airway access, the preferred site below the thyroid cartilage is:
a) Cricothyroid membrane
b) Tracheal rings
c) Thyrohyoid membrane
d) Hyoid bone
Answer: Cricothyroid membrane. This site is accessed in cricothyrotomy due to its superficial location and minimal vascularity, lying between the thyroid cartilage and cricoid cartilage.
3. Which muscle attaches to the posterior lamina of the cricoid cartilage?
a) Posterior cricoarytenoid
b) Cricothyroid
c) Lateral cricoarytenoid
d) Thyroarytenoid
Answer: Posterior cricoarytenoid. This is the only muscle that abducts the vocal cords and is critical for maintaining an open airway.
4. At the C6 vertebral level, which of the following structures is also present?
a) Bifurcation of trachea
b) Beginning of esophagus
c) Termination of aorta
d) Diaphragmatic opening of IVC
Answer: Beginning of esophagus. This level also marks the end of the pharynx and the transition to the esophagus posteriorly.
5. In infants, the narrowest part of the airway is:
a) Vocal cords
b) Cricoid cartilage
c) Thyroid cartilage
d) Tracheal rings
Answer: Cricoid cartilage. In pediatric anatomy, this is the narrowest region and is relevant in airway management, sizing endotracheal tubes, and avoiding post-intubation stenosis.
6. Which nerve is closely related to the cricoid cartilage?
a) Hypoglossal nerve
b) Recurrent laryngeal nerve
c) Phrenic nerve
d) Accessory nerve
Answer: Recurrent laryngeal nerve. This nerve ascends in the tracheoesophageal groove to enter the larynx just behind the cricoid cartilage.
7. Which clinical maneuver involves applying pressure over the cricoid cartilage to prevent aspiration during intubation?
a) Heimlich maneuver
b) Sellick’s maneuver
c) Jaw thrust
d) Chin lift
Answer: Sellick’s maneuver. It occludes the esophagus against the vertebral body to reduce the risk of regurgitation during airway instrumentation.
8. Which ligament connects the cricoid cartilage to the first tracheal ring?
a) Cricothyroid ligament
b) Cricotracheal ligament
c) Thyrohyoid ligament
d) Annular ligament
Answer: Cricotracheal ligament. It provides stability between the cricoid and the trachea while allowing minimal movement.
9. Which imaging modality best visualizes cricoid cartilage in suspected airway trauma?
a) X-ray
b) CT scan
c) MRI
d) Ultrasound
Answer: CT scan. It provides high-resolution images of laryngeal cartilage, detecting fractures or displacement.
10. Which type of cartilage is the cricoid composed of?
a) Elastic cartilage
b) Fibrocartilage
c) Hyaline cartilage
d) Mixed cartilage
Answer: Hyaline cartilage. It maintains airway patency but can ossify with age, becoming more visible on imaging in older individuals.
Chapter: Respiratory System Anatomy
Topic: Trachea and Bronchial Tree
Subtopic: Anatomical Landmarks of Trachea
Key Term Definition
Trachea: A tubular airway extending from the larynx to the carina, conducting air to the bronchi.
Carina: Ridge at the tracheal bifurcation, highly sensitive and triggers the cough reflex.
Bifurcation: Division of the trachea into right and left primary bronchi.
T4 vertebra: Thoracic vertebra marking the level of tracheal bifurcation.
Sternal angle: Surface landmark anteriorly corresponding to T4–T5 vertebral level.
Primary bronchi: First branches of the trachea leading to each lung.
Right main bronchus: Shorter, wider, more vertical bronchus—common site of aspiration.
Left main bronchus: Longer, narrower, more horizontal bronchus.
Bronchoscopy: Endoscopic examination of the airways using a bronchoscope.
Mediastinum: Central compartment of the thoracic cavity containing heart, trachea, esophagus, etc.
Lead Question - 2012:
At what level does the trachea bifurcate?
a) Upper border of T4
b) Lower border of T4
c) 27.5 cm from the incisors
d) Lower border of T5
The correct answer is Lower border of T4. The trachea ends by dividing into right and left main bronchi at the lower border of the T4 vertebra, aligning with the sternal angle anteriorly. This landmark is important in bronchoscopy, thoracic surgery, and chest imaging. It shifts slightly with respiration and posture.
1. Which surface landmark indicates tracheal bifurcation anteriorly?
a) Jugular notch
b) Sternal angle
c) Xiphisternal joint
d) Clavicle
Answer: Sternal angle. The junction between the manubrium and the body of the sternum corresponds to the T4–T5 intervertebral disc level. Clinically, it is a key reference point for rib counting, mediastinal anatomy, and airway localization in surgery or trauma settings.
2. In bronchoscopy, the carina appears:
a) Sharp and well-defined
b) Blunt and indistinct
c) Invisible
d) Covered by epiglottis
Answer: Sharp and well-defined. A normal carina is a distinct ridge; blunting may indicate malignancy or chronic inflammation. Its appearance is crucial during bronchoscopy for diagnosing tumors, lymphadenopathy, or airway compression.
3. Which bronchus is more prone to foreign body aspiration?
a) Right main bronchus
b) Left main bronchus
c) Both equally
d) None
Answer: Right main bronchus. Its shorter, wider, and more vertical course makes it more likely for aspirated objects to enter, especially in children. This anatomical feature explains the distribution of aspiration pneumonia patterns.
4. Which nerve provides sensory innervation to the trachea?
a) Glossopharyngeal nerve
b) Recurrent laryngeal nerve
c) Superior laryngeal nerve
d) Vagus nerve directly
Answer: Recurrent laryngeal nerve. This branch of the vagus nerve supplies sensation to the tracheal mucosa, enabling protective airway reflexes like coughing. Damage can cause impaired reflexes and aspiration risk.
5. Which tracheal layer contains the C-shaped cartilage rings?
a) Mucosa
b) Submucosa
c) Adventitia
d) Fibromuscular membrane
Answer: Adventitia. This outer connective tissue layer contains hyaline cartilage rings, which prevent airway collapse. Posteriorly, the trachea is membranous, allowing expansion of the esophagus during swallowing.
6. In neck flexion, the tracheal bifurcation moves:
a) Upward
b) Downward
c) Remains same
d) Forward only
Answer: Upward. Neck flexion shortens the trachea and elevates the carina, which is relevant during airway management. Excessive movement can complicate tube positioning in intubated patients.
7. Arterial supply of the upper trachea is primarily via:
a) Inferior thyroid artery
b) Superior thyroid artery
c) Bronchial arteries
d) Vertebral artery
Answer: Inferior thyroid artery. This vessel supplies blood to the cervical portion of the trachea, supporting mucosal health and healing. Lower portions receive blood from bronchial arteries.
8. Widening of the carinal angle is suggestive of:
a) Pneumothorax
b) Left atrial enlargement
c) Asthma
d) Emphysema
Answer: Left atrial enlargement. Seen in conditions like mitral stenosis, it causes downward displacement of the carina, visible on imaging and often correlating with clinical symptoms of pulmonary congestion.
9. Structure lying directly posterior to tracheal bifurcation:
a) Esophagus
b) Left atrium
c) Descending aorta
d) Right pulmonary artery
Answer: Esophagus. The esophagus runs behind the trachea and continues posterior to the left main bronchus after bifurcation, important during transesophageal procedures.
10. If an endotracheal tube enters the right bronchus, the consequence is:
a) Hypoventilation of right lung
b) Hypoventilation of left lung
c) Collapse of both lungs
d) Bronchospasm
Answer: Hypoventilation of left lung. The tube bypasses the left bronchus, ventilating only the right lung. This can cause collapse of the left lung if unrecognized during anesthesia or critical care.