Diffusion Across the Alveolar Membrane
- Previous year questions on Diffusion Across the Alveolar Membrane for NEET PG (National Eligibility cum Entrance Test - Postgraduate), from the Physiology section of the exam.
- Most questions here come from previous-year papers of Indian postgraduate medical entrance and licensing exams; where a paper and year are recorded the question carries them. The image-based questions are original vignettes written around an openly licensed figure, and were never asked in any exam.
- 36 live questions in Diffusion Across the Alveolar Membrane.
- 3 of 36 questions carry a verified exam year: 2017, 2018, 2020.
- Physiology is worth about 17 of 300 questions on the exam. See every subject’s weightage.
- Question set last updated 6 Sept 2026.
Q1.A patient presents with right to left shunt. Oxygen content in aerial and venous side are 18 and 14 ml/100 ml respectively. Oxygen content at pulmonary capillary is 20. What is the percentage shunting of cardiac output?
- A23%
- B33%✓ Correct answer
- C43%
- D53%
Q2.when Va/Q is INFINITY , it means
- AThe pO2 of alveolar air is 159mmHg and PCO2 is 40mmHg
- Bpartial pressure of alveolar gas is same as dead space✓ Correct answer
- CPartial pressure of O2 and CO2 are equal
- DALL THE ABOVE
Q3.Which of the following will not cause a low lung diffusing capacity (DL)?
- ADecreased diffusion distance✓ Correct answer
- BDecreased capillary blood volume
- CDecreased surface area
- DDecreased cardiac output
Q4.What will be the PA O2 when FiO2 is 0.5?
- A>100
- B>150
- C>250✓ Correct answer
- D.>500
Q5.What is true regarding (A-a)O2 gradient? (A = alveolus; a = aerial)
- ANormal gradient ~ 15 mmhg (2 kpa)
- BAn increased gradient may be caused by, pulmonary collapse
- CVenous admixture affects (A-a)O2 gradient
- DAll✓ Correct answer
Q6.The transport of CO is diffusion limited because
- ABinds avidly with Hb✓ Correct answer
- BPartial pressure of CO is less
- CCO is less absorbed in water
- DAlveolar membrane is less permeable
Q7.Diffusion capacity of carbon monoxide is decreased in all except:
- APolycythemia✓ Correct answer
- BInterstitial lung disease
- CEmphysema
- DPulmonary vascular disease
Q8.Maximum alveolar aerial oxygen difference is seen in:
- APulmonary embolism✓ Correct answer
- BSevere asthma
- CInterstitial lung disease
- DForeign body in upper airway
Q9.In a normal resting person, breathing air at sea level with RQ of 0.8, Pa CO2 of 40mm Hg, Pi O2 of 149 mm Hg and Fi O2 of 21 %. Calculate alveolar partial pressure of oxygen
- A100 mm Hg✓ Correct answer
- B90 mm Hg
- C120 mm Hg
- D80 mm Hg
Q10.The gradient of alveolar arterial oxygen tension increases in All except
- ADiffusion defect
- BRight left shunt
- CHypoventilation✓ Correct answer
- DVentilation perfusion abnormality
Answer key
Q1: B. 33%; Q2: B. partial pressure of alveolar gas is same as dead space; Q3: A. Decreased diffusion distance; Q4: C. >250; Q5: D. All; Q6: A. Binds avidly with Hb; Q7: A. Polycythemia; Q8: A. Pulmonary embolism; Q9: A. 100 mm Hg; Q10: C. Hypoventilation.
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