Respiratory system: West lung zones: 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: West lung zones

Sample item

A ventilated patient with severe haemorrhage has a very low pulmonary arterial pressure, while positive pressure ventilation raises alveolar pressure. Which lung zone, with ventilation but little or no perfusion, increases?

AZone 4, where interstitial pressure reduces basal flowBZone 1, where alveolar pressure exceeds arterial pressureCZone 2, where arterial pressure exceeds alveolar pressureDZone 3, where venous pressure exceeds alveolar pressure

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

The answer and the reasoning

B. Zone 1, where alveolar pressure exceeds arterial pressure

In West's model, zone 1 has alveolar pressure greater than arterial and venous pressure, so capillaries collapse and the zone is ventilated but not perfused, acting as alveolar dead space. It is absent in normal upright lungs and appears with haemorrhage or positive pressure ventilation.

Option by option

A. Zone 4, where interstitial pressure reduces basal flow
Zone 4 shows reduced flow at the lung base from interstitial pressure, but the capillaries are not collapsed by alveolar pressure.
B. Zone 1, where alveolar pressure exceeds arterial pressure (correct)
Correct. Zone 1 occurs when alveolar pressure exceeds pulmonary arterial pressure.
C. Zone 2, where arterial pressure exceeds alveolar pressure
In zone 2, arterial pressure exceeds alveolar pressure, so flow occurs.
D. Zone 3, where venous pressure exceeds alveolar pressure
In zone 3, both arterial and venous pressures exceed alveolar pressure, so perfusion is continuous.

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 B, Zone 1, where alveolar pressure exceeds arterial pressure. In West's model, zone 1 has alveolar pressure greater than arterial and venous pressure, so capillaries collapse and the zone is ventilated but not perfused, acting as alveolar dead space.

Why is "Zone 4, where interstitial pressure reduces basal flow" not the answer?

Zone 4 shows reduced flow at the lung base from interstitial pressure, but the capillaries are not collapsed by alveolar pressure.

Why is "Zone 2, where arterial pressure exceeds alveolar pressure" not the answer?

In zone 2, arterial pressure exceeds alveolar pressure, so flow occurs.

Why is "Zone 3, where venous pressure exceeds alveolar pressure" not the answer?

In zone 3, both arterial and venous pressures exceed alveolar pressure, so perfusion is continuous.

What concept does this question test?

It tests Respiratory system: West lung zones in Physiology. It is absent in normal upright lungs and appears with haemorrhage or positive pressure ventilation.

How hard is this question?

We tag it as an application question: it asks you to use a fact on a patient or a finding. 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: West lung zones?

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.