Respiratory Physiology (Mechanics, Gas Exchange, PFTs, Regulation) MCQs

Physiology · 74 free questions with answers & explanations.

1. A 60-year-old smoker has FEV1 = 1.2 L, FVC = 2.8 L, and FEV1/FVC ratio = 43%. TLC is 7.5 L. What is the pattern of spirometry abnormality?
2. In a standing individual, alveolar PO2 is highest and ventilation-perfusion ratio (V/Q) is greatest in which lung zone?
3. The primary stimulus that drives respiration under normal resting conditions is:
4. The diffusing capacity of the lungs for CO (DLCO) is reduced in which of the following conditions?
5. Surfactant secreted by type II pneumocytes primarily functions to:
6. On a flow-volume loop obtained during forced spirometry, peak expiratory flow is reduced and the expiratory limb shows a scooped or concave pattern toward the volume axis. The FEV1/FVC ratio is 0.58. What pattern does this represent and which condition is most consistent?
7. A patient is breathing air at sea level. PAO₂ is 100 mmHg, PaO₂ is 80 mmHg, and PaCO₂ is 40 mmHg. Using the alveolar gas equation (FiO₂ = 0.21, PB = 760, PH₂O = 47, RQ = 0.8), what is the A-a gradient and what does elevation suggest?
8. At the apex of an upright lung, ventilation-perfusion (V/Q) ratio is approximately 3.3, while at the base it is 0.6. Which statement correctly predicts the gas exchange consequences of this gradient?
9. The oxyhemoglobin dissociation curve shifts to the right in all of the following conditions EXCEPT:
10. In the oxygen-haemoglobin dissociation curve, 2,3-bisphosphoglycerate (2,3-BPG) reduces haemoglobin's O₂ affinity by:
11. A spirometry report shows FVC of 3.2 L (predicted 4.5 L), FEV1 of 2.6 L (predicted 3.7 L), FEV1/FVC ratio of 81%, TLC reduced on plethysmography. DLCO is reduced. This pattern is most consistent with:
12. The hypoxic ventilatory response is primarily mediated by peripheral chemoreceptors in the carotid bodies. These chemoreceptors detect low PO₂ via which cellular mechanism in type I (glomus) cells?
13. West Zone 1 of the lung (apex in an upright person) has a ventilation-perfusion ratio that is greatly elevated. What is the physiological consequence and why does it not normally cause hypoxaemia at sea level?
14. The oxygen-haemoglobin dissociation curve shifts to the right (decreased O2 affinity) with all of the following EXCEPT:
15. Pulmonary vascular resistance (PVR) is lowest at which lung volume, and what dual mechanism explains this relationship?
16. A patient with Cheyne-Stokes respiration has hypocapnic episodes followed by apnoea. Which mechanism accounts for the oscillating breathing pattern?
17. In a patient with a single-breath nitrogen washout test, a steep phase III slope (elevated delta N2/L > 2%) indicates which pathophysiology?
18. Hering-Breuer inflation reflex is mediated by which receptor type and pathway, and what is its primary physiological role in adult humans?
19. In hypoxic pulmonary vasoconstriction (HPV), the sensor for alveolar hypoxia is located in which cell type, and what is the proposed effector mechanism?
20. The Haldane effect describes which property of CO₂ transport in blood?
21. A patient is noted to have a DLCO (diffusing capacity for CO) that is markedly reduced with normal spirometry. Which condition best explains this pattern?
22. Peripheral chemoreceptors (carotid bodies) are primarily stimulated by which mechanism under sustained hypoxia?
23. What is the physiological basis for the characteristic A-a gradient observed in interstitial lung disease (ILD) — and why does supplemental O₂ reliably correct hypoxemia in ILD but not in significant V/Q mismatch from pulmonary embolism?
24. A patient with obstructive sleep apnea has recurrent nocturnal hypoxia. The peripheral chemoreceptors that primarily detect acute falls in PaO2 are located in the carotid bodies. At which partial pressure of O2 does their firing rate increase most steeply?
25. Surfactant reduces alveolar surface tension and prevents alveolar collapse. According to the Law of Laplace, smaller alveoli tend to collapse into larger ones. Surfactant prevents this because:
26. A patient with pulmonary fibrosis has FVC 60% predicted, FEV1 65% predicted, FEV1/FVC 92%, DLCO 45% predicted. Which mechanism best explains the reduced DLCO in this condition?
27. During maximal exercise, a trained athlete can achieve cardiac outputs of 25-30 L/min. Oxygen extraction from blood increases substantially. The Bohr effect facilitates peripheral O2 unloading during exercise because increased muscle CO2 production:
28. The Hering-Breuer inflation reflex prevents over-inflation of the lungs. The receptors and pathway mediating this reflex are:
29. The Haldane effect refers to the influence of oxygenation on CO₂ carrying capacity of blood. In the pulmonary capillary, oxygenation of hemoglobin increases CO₂ release via which specific molecular mechanism?
30. A patient with severe kyphoscoliosis has a TLC of 2.8 L (predicted 5.2 L), FEV1/FVC ratio of 82%, and normal DLCO. Arterial blood gas shows PaO₂ = 62 mmHg, PaCO₂ = 48 mmHg. The primary mechanism of hypoxemia in this patient is:
31. Type J (juxtacapillary) receptors in the lung parenchyma are stimulated by which conditions and what clinical symptoms do they mediate?
32. In the measurement of pulmonary diffusing capacity (DLCO), carbon monoxide is used as the test gas. The primary reason CO is ideal for this measurement is:
33. The oxygen-hemoglobin dissociation curve undergoes a rightward shift under conditions that favour O₂ unloading at tissues. Which molecular mechanism best explains the Bohr effect at the level of hemoglobin structure?
34. Central chemoreceptors in the ventral medulla respond primarily to changes in CSF pH rather than directly to arterial PaCO₂. Why does CO₂ changes affect CSF pH faster than arterial HCO₃⁻ changes?
35. In a patient with pulmonary embolism causing dead space ventilation, which parameter would most directly reflect the increased dead space fraction (Vd/Vt)?
36. Surfactant reduces surface tension in alveoli. By the Laplace relationship (P = 2T/r), smaller alveoli would have higher pressure and should empty into larger alveoli. The key property of surfactant that prevents this alveolar instability is:
37. The hypoxic ventilatory response (HVR) is primarily mediated by peripheral chemoreceptors in the carotid body. The oxygen-sensing mechanism in glomus cells involves:
38. In a patient with severe obesity hypoventilation syndrome (OHS), the expected arterial blood gas pattern during an awake, resting state is:
39. The oxygen-hemoglobin dissociation curve shifts rightward (decreased O₂ affinity) in all of the following conditions EXCEPT:
40. During forced expiration at low lung volumes (below the equal pressure point), the dynamic airway compression mechanism is explained by the 'Starling resistor model.' At what point does flow become effort-independent, and what sets the flow limit?
41. A 45-year-old woman has DLCO reduced to 45% of predicted with normal spirometry and lung volumes. The most likely explanation for isolated DLCO reduction with normal spirometry is:
42. The peripheral chemoreceptors in the carotid bodies respond to changes in PaO2, PaCO2, and pH. The most potent acute stimulus for increased ventilation via carotid body chemoreceptors in a healthy person is:
43. A patient breathing 100% O2 develops complete right lower lobe atelectasis. The PaO2 remains 90 mmHg despite 100% FiO2. The physiological mechanism responsible for the persistent hypoxemia is:
44. A patient with severe emphysema has a lung compliance of 0.6 L/cmH2O (normal ~0.2 L/cmH2O). Which structural change best explains this?
45. The Hering-Breuer inflation reflex limits tidal volume by:
46. On a flow-volume loop, a patient shows a 'sawtooth' (oscillatory) pattern during tidal inspiration and expiration. This pattern is most characteristic of:
47. A mountaineer ascending to 5000m altitude experiences periodic Cheyne-Stokes breathing during sleep. The mechanism is best explained by:
48. In oxygen-hemoglobin dissociation, the Bohr effect describes the rightward shift of the ODC in acidic conditions. In exercising muscle tissue, multiple factors compound this rightward shift. The correct rank order from GREATEST to LEAST contribution to rightward ODC shift in exercising muscle is:
49. A patient with diffuse alveolar damage has impaired CO2 elimination despite a normal PaCO2 on arterial blood gas. This apparent paradox is explained by:
50. A patient has the following PFT results: FEV1 58% predicted, FVC 82% predicted, FEV1/FVC 54%, TLC 112% predicted, RV 145% predicted. What is the pattern and MOST likely underlying pathology?
51. The Haldane effect describes an important physiological property of hemoglobin. Which statement BEST describes the Haldane effect and its physiological significance?
52. A scuba diver breathing air ascends rapidly from 30 meters. The diver develops sudden dyspnea and frothy sputum within minutes of surfacing. Arterial PaO2 is 45 mmHg. Which mechanism explains this presentation?
53. A patient's spirometry shows FEV1 of 2.1 L, FVC of 2.4 L, FEV1/FVC of 87.5%. TLC measured by helium dilution is 4.2 L (predicted 6.1 L), RV is 1.8 L. What is the MOST likely diagnosis?
54. The hypoxic pulmonary vasoconstriction (HPV) response is unique to the pulmonary circulation. What is the MOST precisely understood molecular mechanism of HPV?
55. At high altitude (4500 m), a climber's alveolar PO2 has dropped and she develops mountain sickness. Her arterial pH is 7.49, PaCO2 is 28 mmHg, and HCO3⁻ is 21 mEq/L. Which sequence of physiological events BEST describes the acclimatization that has occurred?
56. A patient has FVC 3.0 L, FEV1 2.5 L, FEV1/FVC 83%, TLC 5.5 L, RV 2.5 L, DLCO 45% predicted. Which pattern does this represent?
57. The hypoxic pulmonary vasoconstriction (HPV) response serves to improve ventilation-perfusion matching. Which of the following clinical scenarios represents the OPPOSITE of the expected HPV response, potentially worsening V/Q mismatch?
58. A mountaineer ascends to 5500 m altitude (barometric pressure 380 mmHg). After 5 days of acclimatisation, his haemoglobin is 17 g/dL and 2,3-DPG is elevated. Which of the following is the calculated PO2 of inspired air (PiO2) at this altitude, assuming normal FiO2?
59. A patient with idiopathic pulmonary fibrosis (IPF) has reduced DLCO (diffusing capacity for CO) and reduced total lung capacity. In which clinical scenario would DLCO be paradoxically elevated despite normal or reduced lung volumes?
60. The ventilation-perfusion (V/Q) ratio varies between apex and base of an upright lung. Which of the following correctly describes the difference?
61. A patient with moderate COPD undergoes spirometry. FVC is 3.2 L (predicted 4.0 L), FEV1 is 1.6 L (predicted 3.2 L). What is the FEV1/FVC ratio and what pattern does this represent?
62. The peripheral chemoreceptors (carotid and aortic bodies) respond to all of the following stimuli EXCEPT:
63. In a patient with severe emphysema, spirometry shows FEV1/FVC = 0.45, FVC = 80% predicted, TLC = 145% predicted, DLCO = 35% predicted. The markedly reduced DLCO (diffusing capacity) in emphysema is due to:
64. Hypoxic pulmonary vasoconstriction (HPV) diverts blood away from poorly ventilated lung regions. The mechanism of HPV is unique because, unlike systemic vessels, pulmonary arteriolar smooth muscle:
65. The apneustic centre (lower pons) prolongs inspiration; the pneumotaxic centre (upper pons/parabrachial nuclei) limits inspiration and facilitates expiration. A lesion of the pneumotaxic centre alone causes:
66. A patient with obstructive sleep apnea (OSA) undergoes overnight polysomnography showing repetitive apneas of 25–35 seconds with O2 desaturations to 82%. What is the primary mechanism of arousal that terminates each apneic episode?
67. In the alveolar gas equation, the alveolar O2 tension (PAO2) is calculated as: PAO2 = FIO2 × (Patm − PH2O) − (PaCO2/R). At sea level breathing room air (FIO2 = 0.21, Patm = 760 mmHg, PH2O = 47 mmHg, PaCO2 = 40 mmHg, R = 0.8), what is the PAO2, and what is the normal A-a gradient?
68. The oxygen-hemoglobin dissociation curve shifts to the right (reduced O2 affinity) in all of the following conditions EXCEPT:
69. Alveolar-arterial (A-a) oxygen gradient is calculated for a patient breathing room air at sea level (PiO2 = 150 mmHg). If PaCO2 = 40 mmHg and PaO2 = 80 mmHg (RQ = 0.8), what is the A-a gradient, and is it elevated?
70. A 68-year-old man with COPD has FEV1 = 1.2 L, FVC = 2.8 L, FEV1/FVC = 43%, RV = 4.2 L, TLC = 8.0 L, DLCO reduced to 45% predicted. Which pattern is present, and which finding best distinguishes emphysema from chronic bronchitis in this context?
71. Hypoxic pulmonary vasoconstriction (HPV) is a unique reflex diverting blood from poorly ventilated lung regions. Which mediator or mechanism has been most established as the cellular sensor and effector of HPV?
72. A patient with suspected obstructive lung disease has spirometry showing FVC 4.0 L, FEV1 2.4 L, and FEV1/FVC 60%. After bronchodilator, FEV1 improves to 2.88 L. What is the % reversibility and does it confirm bronchial asthma?
73. In the hypoxic ventilatory response (HVR), peripheral chemoreceptors (carotid bodies) are the primary sensors. The carotid body glomus type I cells respond to hypoxaemia by:
74. A patient has a V/Q ratio of 0 in a region of the lung. This region is described as: