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

A patient with COPD breathes out through pursed lips and feels less breathless. How does this help?

AIt raises airway pressure during expiration, keeping small airways open and reducing air trappingBIt lowers pleural pressure during expiration, so airways dilate passivelyCIt raises lung elastic recoil, so the driving pressure for expiration increasesDIt stimulates the Hering-Breuer reflex and so prolongs inspiration

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

The answer and the reasoning

A. It raises airway pressure during expiration, keeping small airways open and reducing air trapping

In emphysema, loss of radial traction makes airways collapse early when pleural pressure rises during forced expiration. Pursed lips create back pressure in the airway, which moves the point where airway pressure equals pleural pressure upstream toward the alveoli, into larger cartilage-supported airways that resist collapse, and keeps the airways open longer, reducing air trapping and dynamic hyperinflation.

Option by option

A. It raises airway pressure during expiration, keeping small airways open and reducing air trapping (correct)
Intraluminal back pressure splints the airways open and lets more gas escape.
B. It lowers pleural pressure during expiration, so airways dilate passively
Pleural pressure rises, not falls, during expiratory effort, and the back pressure acts inside the airway.
C. It raises lung elastic recoil, so the driving pressure for expiration increases
Pursing the lips does not alter elastic recoil, which has been lost through tissue destruction.
D. It stimulates the Hering-Breuer reflex and so prolongs inspiration
The Hering-Breuer reflex limits inspiration through inflation of the lungs and is not engaged by pursing the lips.

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 A, It raises airway pressure during expiration, keeping small airways open and reducing air trapping. In emphysema, loss of radial traction makes airways collapse early when pleural pressure rises during forced expiration.

Why is "It lowers pleural pressure during expiration, so airways dilate passi…" not the answer?

Pleural pressure rises, not falls, during expiratory effort, and the back pressure acts inside the airway.

Why is "It raises lung elastic recoil, so the driving pressure for expiration…" not the answer?

Pursing the lips does not alter elastic recoil, which has been lost through tissue destruction.

Why is "It stimulates the Hering-Breuer reflex and so prolongs inspiration" not the answer?

The Hering-Breuer reflex limits inspiration through inflation of the lungs and is not engaged by pursing the lips.

What concept does this question test?

It tests Respiratory system: dynamic airway compression in Physiology. Pursed lips create back pressure in the airway, which moves the point where airway pressure equals pleural pressure upstream toward the alveoli, into larger cartilage-supported airways that resist collapse, and keeps the airways open longer, reducing air trapping and dynamic hyperinflation.

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: 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.