Cardiovascular: coronary circulation: 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: coronary circulation

Sample item

A 55-year-old man with coronary artery disease develops angina when his heart rate rises from 70 to 150 per minute during exercise. Which mechanism most directly reduces his left ventricular myocardial perfusion at the faster rate?

AFall in myocardial oxygen demandBReduced aortic pressure during systoleCCompression of the coronary ostia during diastoleDShortening of diastole, the period when most left coronary flow occurs

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

The answer and the reasoning

D. Shortening of diastole, the period when most left coronary flow occurs

Left ventricular intramural pressure during systole compresses the coronary vessels, so most left coronary flow occurs in diastole. Tachycardia shortens diastole proportionally more than systole, which reduces perfusion time just as oxygen demand rises. The subendocardium is most vulnerable.

Option by option

A. Fall in myocardial oxygen demand
Oxygen demand rises with heart rate, so a fall in demand would not explain the angina.
B. Reduced aortic pressure during systole
Aortic pressure is usually maintained or raised during exercise and is not the cause.
C. Compression of the coronary ostia during diastole
The ostia are open in diastole, when coronary flow is highest.
D. Shortening of diastole, the period when most left coronary flow occurs (correct)
Correct. Less diastolic time means less coronary filling, especially in a stenosed vessel.

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, Shortening of diastole, the period when most left coronary flow occurs. Left ventricular intramural pressure during systole compresses the coronary vessels, so most left coronary flow occurs in diastole.

Why is "Fall in myocardial oxygen demand" not the answer?

Oxygen demand rises with heart rate, so a fall in demand would not explain the angina.

Why is "Reduced aortic pressure during systole" not the answer?

Aortic pressure is usually maintained or raised during exercise and is not the cause.

Why is "Compression of the coronary ostia during diastole" not the answer?

The ostia are open in diastole, when coronary flow is highest.

What concept does this question test?

It tests Cardiovascular: coronary circulation in Physiology. Tachycardia shortens diastole proportionally more than systole, which reduces perfusion time just as oxygen demand rises. The subendocardium is most vulnerable.

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: coronary circulation?

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.