Respiratory system: phrenic nerve palsy: 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: phrenic nerve palsy

Sample item

A man develops breathlessness after cardiac surgery, and a chest radiograph shows an elevated left hemidiaphragm. On a sniff test under fluoroscopy, the left hemidiaphragm moves upward as he sniffs in. What explains the upward movement?

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

The answer and the reasoning

D. The paralysed hemidiaphragm is pushed up by the negative intrathoracic pressure of inspiration

A paralysed hemidiaphragm lacks tone and contraction. During inspiration the fall in intrathoracic pressure and the rise in abdominal pressure from the working side draw it up in a paradoxical movement. The phrenic nerve (C3 to C5) can be injured in cardiac surgery.

Option by option

  • A. Active contraction of the left diaphragm against raised abdominal pressure

    An active, contracting diaphragm descends during inspiration, not rises.

  • B. Spasm of the left hemidiaphragm from phrenic irritation

    Spasm would flatten and lower the dome, rather than raise it during inspiration.

  • C. Compensatory contraction of the left external intercostals

    The intercostals do not move the diaphragm upward and would not account for paradoxical motion.

  • D. The paralysed hemidiaphragm is pushed up by the negative intrathoracic pressure of inspiration (correct)

    Correct. Without muscle activity the diaphragm passively follows the pressure change.

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.

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Questions about this Physiology question

What is the answer to this Physiology question?

The best answer is D, The paralysed hemidiaphragm is pushed up by the negative intrathoracic pressure of inspiration. A paralysed hemidiaphragm lacks tone and contraction.

Why is "Active contraction of the left diaphragm against raised abdominal pre…" not the answer?

An active, contracting diaphragm descends during inspiration, not rises.

Why is "Spasm of the left hemidiaphragm from phrenic irritation" not the answer?

Spasm would flatten and lower the dome, rather than raise it during inspiration.

Why is "Compensatory contraction of the left external intercostals" not the answer?

The intercostals do not move the diaphragm upward and would not account for paradoxical motion.

What concept does this question test?

It tests Respiratory system: phrenic nerve palsy in Physiology. During inspiration the fall in intrathoracic pressure and the rise in abdominal pressure from the working side draw it up in a paradoxical movement. The phrenic nerve (C3 to C5) can be injured in cardiac surgery.

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: phrenic nerve palsy?

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.