Cardiovascular: heart sounds in atrial septal defect: 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: heart sounds in atrial septal defect

Sample item

A 20-year-old woman has a wide second heart sound whose splitting does not vary with breathing. Which explanation fits an atrial septal defect?

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

The answer and the reasoning

C. Breathing-related changes in venous return are offset by reciprocal shunt flow, so right-sided volume and the split stay fixed

In atrial septal defect the left-to-right shunt volume overloads the right ventricle, prolonging its ejection and delaying P2. During inspiration, extra systemic venous return is offset by a reduced shunt, and in expiration the reverse occurs, so right atrial filling stays steady and the split is fixed. This is called wide fixed splitting.

Option by option

  • A. Left bundle branch block delays aortic valve closure

    Left bundle branch block causes paradoxical splitting, narrowing in inspiration.

  • B. The aortic valve closes late because of left ventricular outflow obstruction

    Late aortic closure would produce reversed splitting, which varies with respiration.

  • C. Breathing-related changes in venous return are offset by reciprocal shunt flow, so right-sided volume and the split stay fixed (correct)

    Correct. Reciprocal shunt flow keeps right-sided volume constant, fixing the split.

  • D. The pulmonary valve closes early because of low pulmonary vascular resistance

    Early P2 would narrow the split, and ASD delays P2 instead.

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 C, Breathing-related changes in venous return are offset by reciprocal shunt flow, so right-sided volume and the split stay fixed. In atrial septal defect the left-to-right shunt volume overloads the right ventricle, prolonging its ejection and delaying P2.

Why is "Left bundle branch block delays aortic valve closure" not the answer?

Left bundle branch block causes paradoxical splitting, narrowing in inspiration.

Why is "The aortic valve closes late because of left ventricular outflow obst…" not the answer?

Late aortic closure would produce reversed splitting, which varies with respiration.

Why is "The pulmonary valve closes early because of low pulmonary vascular re…" not the answer?

Early P2 would narrow the split, and ASD delays P2 instead.

What concept does this question test?

It tests Cardiovascular: heart sounds in atrial septal defect in Physiology. During inspiration, extra systemic venous return is offset by a reduced shunt, and in expiration the reverse occurs, so right atrial filling stays steady and the split is fixed. This is called wide fixed splitting.

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 Cardiovascular: heart sounds in atrial septal defect?

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.