A 24-year-old soldier is flown from Chandigarh to a post in Ladakh at about 3,500 m. Within hours his breathing becomes deeper and faster, with an arterial PO2 of 52 mmHg and PCO2 of 30 mmHg. Which receptors mainly drive this increase in ventilation?

Medullary central chemoreceptors

A 28-year-old software engineer from Bengaluru climbs quickly to 4,200 m on a trek in Himachal. On the third night he has a dry cough, breathlessness at rest, frothy sputum and crackles in both lungs; SpO2 is 68%. What is the main mechanism of his illness?

Uneven hypoxic pulmonary vasoconstriction

Left ventricular failure from hypoxic myocardial damage

Cerebral vasodilatation raising intracranial pressure

Respiratory alkalosis reducing ventilatory drive

A 45-year-old man who has worked as a stone cutter in Rajasthan for 20 years has progressive breathlessness. Chest X-ray shows nodular opacities in the upper zones. Which pattern of lung function tests is most likely?

Low FVC, normal or high FEV1/FVC, low DLCO

Low FVC, low FEV1/FVC, normal DLCO

High total lung capacity and residual volume

Normal FVC, low FEV1/FVC, high DLCO

A 30-year-old man born and raised in Leh comes to a Delhi hospital for a check-up. His haemoglobin is 18.2 g/dL, with no lung or heart disease. Which hormone, and from which site, mainly explains this finding?

Erythropoietin from renal peritubular cells

Erythropoietin from hepatic sinusoidal cells

Lung mechanics, gas exchange and regulation of breathing

23 NEET-PG practice questions on Lung mechanics, gas exchange and regulation of breathing, part of Physiology. The first 23 are below; the first 5 with answers and explanations (tap Show answer after you have chosen), the rest in Learn with a free account.

Question 1 · Medium
A 24-year-old soldier is flown from Chandigarh to a post in Ladakh at about 3,500 m. Within hours his breathing becomes deeper and faster, with an arterial PO2 of 52 mmHg and PCO2 of 30 mmHg. Which receptors mainly drive this increase in ventilation?
1. APulmonary stretch receptors
2. BJuxtacapillary (J) receptors
3. CCarotid body chemoreceptors
4. DMedullary central chemoreceptors
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Answer: C · Carotid body chemoreceptors
The peripheral chemoreceptors, mainly the carotid bodies, sense a fall in arterial PO2 and signal the medulla through the glossopharyngeal nerve. They fire steeply once PO2 falls below about 60 mmHg, so hypoxic hyperventilation begins at altitude. The resulting fall in PCO2 makes the CSF alkaline, which actually restrains the central chemoreceptors in the first days. Over several days the kidneys excrete bicarbonate, this brake is lifted and ventilation rises further (acclimatisation); acetazolamide speeds this process.
- A: Stretch receptors mediate the Hering-Breuer reflex and do not sense oxygen.
- B: J receptors respond to pulmonary congestion and oedema, causing rapid shallow breathing.
- D: Central chemoreceptors respond to CSF H+ from CO2, not to hypoxia, and are restrained by the low PCO2.
Question 2 · Medium
A 28-year-old software engineer from Bengaluru climbs quickly to 4,200 m on a trek in Himachal. On the third night he has a dry cough, breathlessness at rest, frothy sputum and crackles in both lungs; SpO2 is 68%. What is the main mechanism of his illness?
1. ALeft ventricular failure from hypoxic myocardial damage
2. BCerebral vasodilatation raising intracranial pressure
3. CRespiratory alkalosis reducing ventilatory drive
4. DUneven hypoxic pulmonary vasoconstriction
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Answer: D · Uneven hypoxic pulmonary vasoconstriction
This is high-altitude pulmonary oedema. Alveolar hypoxia constricts pulmonary arterioles, but unevenly: blood is forced at high pressure through the less constricted regions, whose capillaries leak and rupture, giving patchy non-cardiogenic oedema with normal left heart pressures. Rapid ascent and individual susceptibility increase risk. Immediate descent and oxygen are the treatment, with nifedipine to lower pulmonary artery pressure.
- A: Left ventricular function and wedge pressure are normal in HAPE.
- B: Cerebral vasodilatation underlies high-altitude cerebral oedema, which presents with confusion and ataxia.
- C: Alkalosis restrains ventilation but does not cause pulmonary oedema.
Question 3 · Medium
A 45-year-old man who has worked as a stone cutter in Rajasthan for 20 years has progressive breathlessness. Chest X-ray shows nodular opacities in the upper zones. Which pattern of lung function tests is most likely?
1. ALow FVC, normal or high FEV1/FVC, low DLCO
2. BLow FVC, low FEV1/FVC, normal DLCO
3. CHigh total lung capacity and residual volume
4. DNormal FVC, low FEV1/FVC, high DLCO
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Answer: A · Low FVC, normal or high FEV1/FVC, low DLCO
Silicosis is a fibrotic, restrictive lung disease. Stiff lungs reduce lung volumes, so FVC and total lung capacity fall; FEV1 falls in proportion, and the high elastic recoil keeps the airways open, so FEV1/FVC is normal or even high. Thickened alveolar walls and loss of capillary bed lower the diffusing capacity (DLCO). Silicosis also raises the risk of tuberculosis, so these workers need screening for TB.
- B: A low ratio indicates obstruction; fibrosis also lowers DLCO.
- C: Raised TLC and RV indicate hyperinflation, as in emphysema.
- D: A low ratio with normal FVC is the pattern of airflow obstruction, and DLCO would not rise.
Question 4 · Easy
A 60-year-old man with COPD has spirometry before a hernia repair. The physician also wants his functional residual capacity, which needs body plethysmography or helium dilution. Which lung volume prevents spirometry alone from measuring it?
1. AResidual volume
2. BExpiratory reserve volume
3. CTidal volume
4. DInspiratory reserve volume
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Answer: A · Residual volume
A spirometer records only air that moves in and out of the mouth. Residual volume, the air left after a maximal expiration, never leaves the lungs, so it and every capacity that contains it (functional residual capacity and total lung capacity) need gas dilution, nitrogen washout or body plethysmography. In COPD, air trapping raises residual volume and FRC. Body plethysmography also detects trapped gas that dilution methods miss.
- B: Expiratory reserve volume is exhaled and so is measured by spirometry.
- C: Tidal volume is breathed in and out and is recorded directly.
- D: Inspiratory reserve volume is inhaled and so is measured by spirometry.
Question 5 · Easy
A 30-year-old man born and raised in Leh comes to a Delhi hospital for a check-up. His haemoglobin is 18.2 g/dL, with no lung or heart disease. Which hormone, and from which site, mainly explains this finding?
1. AThrombopoietin from the liver
2. BTestosterone from Leydig cells
3. CErythropoietin from hepatic sinusoidal cells
4. DErythropoietin from renal peritubular cells
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Answer: D · Erythropoietin from renal peritubular cells
Chronic hypoxia at altitude stabilises hypoxia-inducible factor in peritubular interstitial cells of the renal cortex, which increase erythropoietin output. Erythropoietin stimulates red cell precursors in the marrow, raising haemoglobin and oxygen-carrying capacity over weeks. The liver is the main source in fetal life and makes only a small share in adults. Excessive polycythaemia in highlanders can cause chronic mountain sickness.
- A: Thrombopoietin regulates platelet production, not red cells.
- B: Testosterone modestly raises haemoglobin but is not the hypoxic response.
- C: The liver is the main source in the fetus; the kidney dominates in adults.
Question 6 · Easy
On a cold January night in Lucknow, a family of four sleeps in a closed room with a burning coal angithi. In the morning they are drowsy with headache and vomiting. The father's arterial PO2 is 96 mmHg on room air. Which type of hypoxia do they have?
1. AHistotoxic hypoxia
2. BStagnant hypoxia
3. CHypoxic hypoxia
4. DAnaemic hypoxia
Answer and explanation in LearnFree account
Question 7 · Medium
A 19-year-old swimmer takes 20 rapid deep breaths at the edge of a pool so that he can stay underwater longer. During a long underwater length he loses consciousness without feeling any urge to surface. What explains this?
1. AHyperventilation lowers the oxygen stores of haemoglobin
2. BRaised PaCO2 directly depresses the cerebral cortex
3. CA low starting PaCO2 delays the urge while PaO2 falls
4. DCold water stimulates the carotid bodies to stop breathing
Answer and explanation in LearnFree account
Question 8 · Hard
A 35-year-old farmer from Thrissur with leptospirosis develops ARDS and is ventilated in the ICU. With a tidal volume of 500 mL, the peak airway pressure is 35 cmH2O, the plateau pressure during an inspiratory hold is 30 cmH2O and PEEP is 5 cmH2O. What is his static respiratory system compliance?
1. A20 mL/cmH2O
2. B100 mL/cmH2O
3. C14.3 mL/cmH2O
4. D16.7 mL/cmH2O
Answer and explanation in LearnFree account
Question 9 · Medium
A 34-year-old man with right lower lobe pneumonia has a PaO2 of 54 mmHg on room air. On 100% oxygen by a non-rebreathing mask his PaO2 rises only to 68 mmHg. What is the main cause of his hypoxaemia?
1. ARight-to-left shunt through consolidated lung
2. BAlveolar hypoventilation from muscle fatigue
3. CDiffusion limitation across a thick membrane
4. DMild ventilation-perfusion mismatch
Answer and explanation in LearnFree account
Question 10 · Medium
A term newborn in the postnatal ward has an umbilical venous PO2 of only about 30 mmHg in utero yet had normal growth and no acidosis. Fetal haemoglobin made this possible. Why does HbF have a higher oxygen affinity than adult haemoglobin?
1. AIt has four haem groups per alpha chain
2. BIts gamma chains bind 2,3-BPG poorly
3. CIt lacks the Bohr effect of adult haemoglobin
4. DIts beta chains bind oxygen more tightly
Answer and explanation in LearnFree account
Question 11 · Medium
A 38-year-old worker in an electroplating unit in Moradabad collapses after an accidental exposure. He has rapid breathing, lactic acidosis and bright red venous blood. Arterial PO2 is 98 mmHg, and the central venous oxygen saturation is 90%. What is the mechanism of his hypoxia?
1. ABinding of haemoglobin by carbon monoxide
2. BInhibition of cytochrome c oxidase
3. COxidation of haemoglobin to methaemoglobin
4. DLow alveolar PO2 from a poisoned atmosphere
Answer and explanation in LearnFree account
Question 12 · Medium
An ICU registrar reviews four patients: 1. A man with falciparum malaria and a temperature of 40 °C. 2. A girl in diabetic ketoacidosis with pH 7.12. 3. A woman with long-standing iron deficiency anaemia. 4. A man rescued from a smoke-filled room with carboxyhaemoglobin of 25%. In which patients is the oxyhaemoglobin dissociation curve shifted to the right?
1. A1, 2 and 3 only
2. B1 and 4 only
3. C2, 3 and 4 only
4. D1 and 2 only
Answer and explanation in LearnFree account
Question 13 · Medium
A 66-year-old man who smoked for 45 years has a barrel-shaped chest and breathes out through pursed lips. CT shows panlobular emphysema. Which change in lung mechanics is present?
1. AReduced compliance with increased elastic recoil
2. BNormal compliance with raised chest wall recoil
3. CReduced compliance from surfactant deficiency
4. DIncreased compliance with reduced elastic recoil
Answer and explanation in LearnFree account
Question 14 · Easy
A baby born at 29 weeks in a district hospital develops grunting, chest retractions and cyanosis within an hour of birth. The chest X-ray shows a ground-glass appearance with air bronchograms. A deficiency of a product of which cell causes this condition?
1. AType I alveolar cells
2. BClub (Clara) cells
3. CType II alveolar cells
4. DAlveolar macrophages
Answer and explanation in LearnFree account
Question 15 · Medium
A 72-year-old man with dilated cardiomyopathy (ejection fraction 25%) is in the medical ward. At night his breathing waxes and wanes in depth, with pauses of 15-20 seconds between cycles. What mainly causes this breathing pattern?
1. AUpper airway collapse during deep sleep
2. BSlow circulation delaying chemoreceptor feedback
3. CHering-Breuer reflex from overinflated lungs
4. DPulmonary oedema stimulating the J receptors
Answer and explanation in LearnFree account
Question 16 · Medium
A 47-year-old man with diabetes from a slum in Mumbai has reactivated pulmonary tuberculosis, and his chest X-ray shows a cavity in the right apex. Which property of the upright lung helps explain why reactivation favours the apices?
1. AMost compliant alveoli at functional residual capacity
2. BLowest ventilation and alveolar PO2
3. CHighest ventilation-perfusion ratio and alveolar PO2
4. DHighest blood flow and delivery of nutrients
Answer and explanation in LearnFree account
Question 17 · Medium
A 50-year-old woman on day 6 after a total hip replacement suddenly becomes breathless with pleuritic pain and a pulse of 120/min. CT pulmonary angiography shows a large clot in the right lower lobe artery. What happens to the ventilation-perfusion ratio of the lung beyond the clot?
1. AIt falls because ventilation shifts to that lobe
2. BIt falls towards zero, creating a shunt
3. CIt rises towards infinity, adding to dead space
4. DIt stays normal because both fall together
Answer and explanation in LearnFree account
Question 18 · Easy
A 32-year-old woman with massive postpartum haemorrhage receives eight units of packed red cells, several of them near the end of their storage period. How does the oxygen affinity of the transfused haemoglobin compare with that of her own cells?
1. AHigher, because 2,3-BPG is depleted in storage
2. BLower, because 2,3-BPG accumulates in storage
3. CLower, because stored blood is acidic
4. DHigher, because stored cells contain HbF
Answer and explanation in LearnFree account
Question 19 · Hard
A 26-year-old woman from a tribal block in Jharkhand has severe anaemia from hookworm infection: haemoglobin 6 g/dL, PaO2 98 mmHg, SaO2 98%. Using 1.34 mL O2 per gram of haemoglobin and 0.003 mL/dL per mmHg for dissolved oxygen, what is her arterial oxygen content?
1. AAbout 8.2 mL/dL
2. BAbout 7.9 mL/dL
3. CAbout 0.3 mL/dL
4. DAbout 19.9 mL/dL
Answer and explanation in LearnFree account
Question 20 · Hard
A 70-year-old woman with four fractured ribs after a fall breathes shallowly because of pain, with a tidal volume of 250 mL at 32 breaths/min. Before the injury she breathed 500 mL at 16/min. Taking anatomical dead space as 150 mL, what is her alveolar ventilation now?
1. A5.6 L/min
2. B3.2 L/min
3. C8.0 L/min
4. D4.8 L/min
Answer and explanation in LearnFree account
Question 21 · Medium
A 30-year-old woman who was ventilated for 12 days after organophosphate poisoning returns two months later with noisy breathing and breathlessness on exertion. Her flow-volume loop shows a flat plateau in both the inspiratory and expiratory limbs. What is the most likely cause?
1. AVariable intrathoracic obstruction from a tumour
2. BVariable extrathoracic obstruction from vocal cord palsy
3. CFixed tracheal stenosis after intubation
4. DRestrictive defect from residual lung fibrosis
Answer and explanation in LearnFree account
Question 22 · Hard
A 23-year-old man is brought to casualty after injecting heroin. He is drowsy with pinpoint pupils and a respiratory rate of 6/min. ABG on room air at sea level: PaO2 60 mmHg, PaCO2 70 mmHg. Using PAO2 = 150 - PaCO2/0.8, what is his alveolar-arterial (A-a) oxygen gradient, and what is the cause of his hypoxaemia?
1. AAbout 2.5 mmHg; diffusion limitation
2. BAbout 90 mmHg; non-cardiogenic oedema
3. CAbout 2.5 mmHg; pure hypoventilation
4. DAbout 20 mmHg; ventilation-perfusion mismatch
Answer and explanation in LearnFree account
Question 23 · Hard
A 25-year-old army recruit from Kerala is posted to a camp at about 4,000 m. After three weeks the medical officer reviews four statements about his acclimatisation: 1. His haemoglobin has risen because of erythropoietin. 2. His red cell 2,3-BPG has increased. 3. His kidneys excreted extra bicarbonate in the first days. 4. His pulmonary arterial pressure has fallen below his sea-level value. Which statements are correct?
1. A1 and 3 only
2. B1, 2 and 4 only
3. C1, 2 and 3 only
4. D2 and 4 only
Answer and explanation in LearnFree account

Lung mechanics, gas exchange and regulation of breathing

A 24-year-old soldier is flown from Chandigarh to a post in Ladakh at about 3,500 m. Within hours his breathing becomes deeper and faster, with an arterial PO2 of 52 mmHg and PCO2 of 30 mmHg. Which receptors mainly drive this increase in ventilation?

A 28-year-old software engineer from Bengaluru climbs quickly to 4,200 m on a trek in Himachal. On the third night he has a dry cough, breathlessness at rest, frothy sputum and crackles in both lungs; SpO2 is 68%. What is the main mechanism of his illness?

A 45-year-old man who has worked as a stone cutter in Rajasthan for 20 years has progressive breathlessness. Chest X-ray shows nodular opacities in the upper zones. Which pattern of lung function tests is most likely?

A 60-year-old man with COPD has spirometry before a hernia repair. The physician also wants his functional residual capacity, which needs body plethysmography or helium dilution. Which lung volume prevents spirometry alone from measuring it?

A 30-year-old man born and raised in Leh comes to a Delhi hospital for a check-up. His haemoglobin is 18.2 g/dL, with no lung or heart disease. Which hormone, and from which site, mainly explains this finding?

On a cold January night in Lucknow, a family of four sleeps in a closed room with a burning coal angithi. In the morning they are drowsy with headache and vomiting. The father's arterial PO2 is 96 mmHg on room air. Which type of hypoxia do they have?

A 19-year-old swimmer takes 20 rapid deep breaths at the edge of a pool so that he can stay underwater longer. During a long underwater length he loses consciousness without feeling any urge to surface. What explains this?

A 35-year-old farmer from Thrissur with leptospirosis develops ARDS and is ventilated in the ICU. With a tidal volume of 500 mL, the peak airway pressure is 35 cmH2O, the plateau pressure during an inspiratory hold is 30 cmH2O and PEEP is 5 cmH2O. What is his static respiratory system compliance?

A 34-year-old man with right lower lobe pneumonia has a PaO2 of 54 mmHg on room air. On 100% oxygen by a non-rebreathing mask his PaO2 rises only to 68 mmHg. What is the main cause of his hypoxaemia?

A term newborn in the postnatal ward has an umbilical venous PO2 of only about 30 mmHg in utero yet had normal growth and no acidosis. Fetal haemoglobin made this possible. Why does HbF have a higher oxygen affinity than adult haemoglobin?

A 38-year-old worker in an electroplating unit in Moradabad collapses after an accidental exposure. He has rapid breathing, lactic acidosis and bright red venous blood. Arterial PO2 is 98 mmHg, and the central venous oxygen saturation is 90%. What is the mechanism of his hypoxia?

A 66-year-old man who smoked for 45 years has a barrel-shaped chest and breathes out through pursed lips. CT shows panlobular emphysema. Which change in lung mechanics is present?

A baby born at 29 weeks in a district hospital develops grunting, chest retractions and cyanosis within an hour of birth. The chest X-ray shows a ground-glass appearance with air bronchograms. A deficiency of a product of which cell causes this condition?

A 72-year-old man with dilated cardiomyopathy (ejection fraction 25%) is in the medical ward. At night his breathing waxes and wanes in depth, with pauses of 15-20 seconds between cycles. What mainly causes this breathing pattern?

A 47-year-old man with diabetes from a slum in Mumbai has reactivated pulmonary tuberculosis, and his chest X-ray shows a cavity in the right apex. Which property of the upright lung helps explain why reactivation favours the apices?

A 50-year-old woman on day 6 after a total hip replacement suddenly becomes breathless with pleuritic pain and a pulse of 120/min. CT pulmonary angiography shows a large clot in the right lower lobe artery. What happens to the ventilation-perfusion ratio of the lung beyond the clot?

A 32-year-old woman with massive postpartum haemorrhage receives eight units of packed red cells, several of them near the end of their storage period. How does the oxygen affinity of the transfused haemoglobin compare with that of her own cells?

A 26-year-old woman from a tribal block in Jharkhand has severe anaemia from hookworm infection: haemoglobin 6 g/dL, PaO2 98 mmHg, SaO2 98%. Using 1.34 mL O2 per gram of haemoglobin and 0.003 mL/dL per mmHg for dissolved oxygen, what is her arterial oxygen content?

A 70-year-old woman with four fractured ribs after a fall breathes shallowly because of pain, with a tidal volume of 250 mL at 32 breaths/min. Before the injury she breathed 500 mL at 16/min. Taking anatomical dead space as 150 mL, what is her alveolar ventilation now?

A 30-year-old woman who was ventilated for 12 days after organophosphate poisoning returns two months later with noisy breathing and breathlessness on exertion. Her flow-volume loop shows a flat plateau in both the inspiratory and expiratory limbs. What is the most likely cause?