Cardiovascular system: the transplanted denervated heart: 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 · Cardiovascular system: the transplanted denervated heart

Sample item

Six months after orthotopic heart transplantation, a man has a resting heart rate of 100 per minute. During exercise his rate rises slowly and it recovers slowly afterwards. Which explanation fits?

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

The answer and the reasoning

A. Absent vagal tone unmasks the faster intrinsic rate, and changes depend on circulating catecholamines

The donor heart has no autonomic nerve supply, so the sinoatrial node fires at its intrinsic rate of about 100 per minute without vagal restraint. Heart rate changes with exercise rely on circulating catecholamines, so they appear late and fade slowly. The Frank-Starling mechanism still operates in early exercise.

Option by option

  • A. Absent vagal tone unmasks the faster intrinsic rate, and changes depend on circulating catecholamines (correct)

    Correct. Without vagal restraint the intrinsic rate is revealed, and adrenaline takes time to act.

  • B. Persistent sympathetic overactivity driven by the carotid sinus

    The baroreflex cannot reach a denervated node, so the carotid sinus does not drive it.

  • C. Hyperthyroidism induced by immunosuppressive drugs

    Immunosuppressants do not cause hyperthyroidism, and this pattern follows from denervation.

  • D. Complete reinnervation of the sinus node by sympathetic fibres

    Reinnervation is at most partial and late; it does not explain this early picture.

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 A, Absent vagal tone unmasks the faster intrinsic rate, and changes depend on circulating catecholamines. The donor heart has no autonomic nerve supply, so the sinoatrial node fires at its intrinsic rate of about 100 per minute without vagal restraint.

Why is "Persistent sympathetic overactivity driven by the carotid sinus" not the answer?

The baroreflex cannot reach a denervated node, so the carotid sinus does not drive it.

Why is "Hyperthyroidism induced by immunosuppressive drugs" not the answer?

Immunosuppressants do not cause hyperthyroidism, and this pattern follows from denervation.

Why is "Complete reinnervation of the sinus node by sympathetic fibres" not the answer?

Reinnervation is at most partial and late; it does not explain this early picture.

What concept does this question test?

It tests Cardiovascular system: the transplanted denervated heart in Physiology. Heart rate changes with exercise rely on circulating catecholamines, so they appear late and fade slowly. The Frank-Starling mechanism still operates in early exercise.

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 Cardiovascular system: the transplanted denervated heart?

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.