Gas Exchange — Respiratory Physiology

Gas Exchange MCQs: practice questions

Sample Gas Exchange multiple-choice questions from Respiratory Physiology.

1. The alveolar gas equation shows that alveolar PO2 decreases when:

   • A. Ventilation increases
   • B. Inspired PO2 increases
   • C. Respiratory quotient decreases without other changes
   • D. Barometric pressure increases
   • E. Alveolar PCO2 increases

2. In complete airway obstruction, the affected region behaves like:

   • A. Normal lung
   • B. Dead space
   • C. High V/Q
   • D. A shunt
   • E. A region with infinite ventilation

3. The amount of a gas dissolved in blood is proportional to its:

   • A. Partial pressure
   • B. Total blood volume only
   • C. Hemoglobin concentration only
   • D. RBC count only
   • E. Airway resistance

4. Gas diffusion across the respiratory membrane increases with:

   • A. Greater membrane thickness
   • B. Greater surface area
   • C. Smaller pressure gradient
   • D. Lower gas solubility
   • E. Lower diffusion coefficient

5. A right-to-left shunt causes hypoxemia because:

   • A. Inspired PO2 increases
   • B. Ventilation exceeds perfusion in all alveoli
   • C. Deoxygenated blood enters systemic arterial blood
   • D. Hemoglobin concentration falls immediately
   • E. The A–a gradient becomes zero

6. Pulmonary fibrosis impairs gas exchange primarily by:

7. The respiratory exchange ratio is defined as:

8. The normal A–a O2 gradient is approximately:

9. Dalton's law states that partial pressure equals:

10. Normally, pulmonary capillary blood reaches equilibrium with alveolar O2 before leaving the capillary because:

11. O2 and CO2 diffuse across the alveolar membrane primarily by:

12. If alveolar PO2 is 100 mm Hg and pulmonary capillary PO2 is 40 mm Hg, O2 initially diffuses:

13. During strenuous exercise, diffusion remains effective partly because:

14. A V/Q defect typically causes:

15. A decrease in alveolar surface area would be expected to:

16. The driving force for diffusion of O2 across the alveolar-capillary membrane is the:

17. Pure hypoventilation typically produces:

18. If alveolar PCO2 is 40 mm Hg and venous pulmonary capillary PCO2 is 46 mm Hg, CO2 diffuses:

19. In a pulmonary embolus, the affected region behaves physiologically like:

20. In a perfused but completely unventilated lung unit, V/Q is:

21. At normal alveolar gas values, PAO2 is approximately:

22. The physiologic shunt causes arterial PO2 to be slightly lower than alveolar PO2 because:

23. Normal alveolar PCO2 is approximately:

24. Normal average V/Q ratio for the whole lung is approximately:

25. In a ventilated but completely unperfused lung unit, V/Q is:

26. An increased A–a gradient suggests:

27. The partial pressure of O2 in dry air at 760 mm Hg is approximately:

28. Compared with O2, CO2 is more readily diffused because it is:

29. High altitude causes hypoxemia with a:

30. The PO2 of humidified tracheal air at 37°C is approximately: