Respiratory system: dynamic airway compression: 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: dynamic airway compression

Sample item

In a patient with emphysema, forced expiration causes airways to collapse early and expiratory flow reaches a plateau despite greater effort. What change explains the early collapse?

ASurfactant deficiency raises alveolar surface tensionBIncreased elastic recoil narrows the small airwaysCThe equal pressure point moves toward the mouth because airway pressure risesDThe equal pressure point moves toward the alveoli because radial traction is lost

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

The answer and the reasoning

D. The equal pressure point moves toward the alveoli because radial traction is lost

During forced expiration, pressure inside the airway falls along its length until it equals the pleural pressure at the equal pressure point, downstream of which the airway is compressed. In emphysema, elastic recoil and the radial traction that holds small airways open are lost, and the equal pressure point moves toward the alveoli into airways without cartilage, so they collapse early.

Option by option

A. Surfactant deficiency raises alveolar surface tension
Surfactant deficiency causes collapse of alveoli in respiratory distress syndrome and not this airway collapse.
B. Increased elastic recoil narrows the small airways
Elastic recoil is decreased in emphysema, not increased.
C. The equal pressure point moves toward the mouth because airway pressure rises
In emphysema the shift is toward the alveoli, not toward the mouth.
D. The equal pressure point moves toward the alveoli because radial traction is lost (correct)
Correct. Loss of recoil and traction moves the equal pressure point peripherally.

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, The equal pressure point moves toward the alveoli because radial traction is lost. During forced expiration, pressure inside the airway falls along its length until it equals the pleural pressure at the equal pressure point, downstream of which the airway is compressed.

Why is "Surfactant deficiency raises alveolar surface tension" not the answer?

Surfactant deficiency causes collapse of alveoli in respiratory distress syndrome and not this airway collapse.

Why is "Increased elastic recoil narrows the small airways" not the answer?

Elastic recoil is decreased in emphysema, not increased.

Why is "The equal pressure point moves toward the mouth because airway pressu…" not the answer?

In emphysema the shift is toward the alveoli, not toward the mouth.

What concept does this question test?

It tests Respiratory system: dynamic airway compression in Physiology. In emphysema, elastic recoil and the radial traction that holds small airways open are lost, and the equal pressure point moves toward the alveoli into airways without cartilage, so they collapse early.

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: dynamic airway compression?

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.