Cardiac output: Fick principle: 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 · Cardiac output: Fick principle

Sample item

During cardiac catheterisation, oxygen consumption is 300 mL/min, arterial oxygen content is 200 mL/L and mixed venous oxygen content from the pulmonary artery is 150 mL/L. What is the cardiac output?

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

The answer and the reasoning

B. 6.0 L/min

By the Fick principle, cardiac output equals oxygen consumption divided by the arteriovenous oxygen content difference. The difference is 200 minus 150, which is 50 mL/L, so the output is 300 / 50 = 6 L/min. The sample must come from the pulmonary artery to represent properly mixed venous blood.

Option by option

  • A. 0.86 L/min

    0.86 L/min results from dividing by the sum of the contents, 300 / 350.

  • B. 6.0 L/min (correct)

    Correct. 300 / 50 equals 6 L/min.

  • C. 2.0 L/min

    2.0 L/min results from dividing by the venous content alone, 300 / 150.

  • D. 1.5 L/min

    1.5 L/min results from dividing by the arterial content alone, 300 / 200.

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 B, 6.0 L/min. By the Fick principle, cardiac output equals oxygen consumption divided by the arteriovenous oxygen content difference.

Why is "0.86 L/min" not the answer?

0.86 L/min results from dividing by the sum of the contents, 300 / 350.

Why is "2.0 L/min" not the answer?

2.0 L/min results from dividing by the venous content alone, 300 / 150.

Why is "1.5 L/min" not the answer?

1.5 L/min results from dividing by the arterial content alone, 300 / 200.

What concept does this question test?

It tests Cardiac output: Fick principle in Physiology. The difference is 200 minus 150, which is 50 mL/L, so the output is 300 / 50 = 6 L/min. The sample must come from the pulmonary artery to represent properly mixed venous blood.

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 Cardiac output: Fick principle?

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.