Respiratory system: pulmonary vascular resistance and lung volume: practice question

A Physiology question in the style of the NEET PG paper. Answer it first, then read why the right option is right and why each of the others is wrong.

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Physiology · Respiratory system: pulmonary vascular resistance and lung volume

Sample item

A volunteer slowly inflates the lungs from functional residual capacity to total lung capacity. How does pulmonary vascular resistance change?

AIt falls, because all vessels are widened by tractionBIt falls because hypoxic vasoconstriction is relievedCIt stays constant because the pulmonary circulation is a fixed resistanceDIt rises, because the alveolar vessels are stretched and compressed by the expanded alveoli

Original practice item, not a recalled exam question. Nothing here is recorded.

The answer and the reasoning

D. It rises, because the alveolar vessels are stretched and compressed by the expanded alveoli

Pulmonary vascular resistance is lowest near FRC. At high lung volumes the alveolar capillaries are stretched and compressed, which raises resistance, while at low volumes the extra-alveolar vessels narrow as radial traction is lost, so the curve is U-shaped.

Option by option

A. It falls, because all vessels are widened by traction
Traction widens only the extra-alveolar vessels, and it is outweighed by alveolar vessel compression at high volume.
B. It falls because hypoxic vasoconstriction is relieved
Hypoxic vasoconstriction is not altered by a deep breath of air.
C. It stays constant because the pulmonary circulation is a fixed resistance
Resistance varies with lung volume rather than being fixed.
D. It rises, because the alveolar vessels are stretched and compressed by the expanded alveoli (correct)
Correct. Distension of alveoli compresses the capillaries in their walls.

Source note: Original NextPrep sample item — pending expert review. This item is original practice material awaiting independent expert review, so confirm important facts in a standard textbook.

Questions about this Physiology question

What is the answer to this Physiology question?

The best answer is D, It rises, because the alveolar vessels are stretched and compressed by the expanded alveoli. Pulmonary vascular resistance is lowest near FRC.

Why is "It falls, because all vessels are widened by traction" not the answer?

Traction widens only the extra-alveolar vessels, and it is outweighed by alveolar vessel compression at high volume.

Why is "It falls because hypoxic vasoconstriction is relieved" not the answer?

Hypoxic vasoconstriction is not altered by a deep breath of air.

Why is "It stays constant because the pulmonary circulation is a fixed resist…" not the answer?

Resistance varies with lung volume rather than being fixed.

What concept does this question test?

It tests Respiratory system: pulmonary vascular resistance and lung volume in Physiology. At high lung volumes the alveolar capillaries are stretched and compressed, which raises resistance, while at low volumes the extra-alveolar vessels narrow as radial traction is lost, so the curve is U-shaped.

How hard is this question?

We tag it as a multi-step question: it asks you to combine more than one idea. The tag is our own editorial judgement, not an official difficulty rating, so read the reason for every option, not only the answer.

How should I study Respiratory system: pulmonary vascular resistance and lung volume?

For each system, sketch the key graph (pressure–volume loop, oxygen dissociation curve, nephron handling) and explain it aloud. Then use the flashcards and the other Physiology questions on this site to test what stuck.

Is this a real NEET PG question?

No. It is an original practice item (editorial status: sample, version 1). NextPrep does not publish recalled or leaked questions, and independent faculty review of this item has not been completed yet, so confirm important facts in a standard textbook.