Respiratory system: anaerobic threshold and ventilation: 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: anaerobic threshold and ventilation

Sample item

During an incremental treadmill test, minute ventilation starts rising out of proportion to oxygen uptake at a certain work rate. Which stimulus mainly accounts for this inflection?

ALactic acidosis stimulating the carotid bodies and the extra CO2 from bicarbonate bufferingBReduced pulmonary stretch receptor activityCWithdrawal of vagal tone to the airwaysDA sudden fall in arterial PO2 detected by central chemoreceptors

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

The answer and the reasoning

A. Lactic acidosis stimulating the carotid bodies and the extra CO2 from bicarbonate buffering

Above the anaerobic threshold lactate accumulates, and bicarbonate buffering generates additional CO2. The rise in hydrogen ion drives the peripheral chemoreceptors and ventilation climbs faster than oxygen uptake. Arterial PO2 and PCO2 stay close to normal during moderate exercise.

Option by option

A. Lactic acidosis stimulating the carotid bodies and the extra CO2 from bicarbonate buffering (correct)
Correct. Lactic acidosis and buffer-derived CO2 stimulate breathing beyond the oxygen cost of work.
B. Reduced pulmonary stretch receptor activity
Stretch receptor input does not rise out of proportion at this work rate.
C. Withdrawal of vagal tone to the airways
Changes in vagal tone do not explain this nonlinear rise.
D. A sudden fall in arterial PO2 detected by central chemoreceptors
Arterial PO2 remains near normal in exercise, and the central chemoreceptors respond to CO2 and CSF hydrogen ion.

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 A, Lactic acidosis stimulating the carotid bodies and the extra CO2 from bicarbonate buffering. Above the anaerobic threshold lactate accumulates, and bicarbonate buffering generates additional CO2.

Why is "Reduced pulmonary stretch receptor activity" not the answer?

Stretch receptor input does not rise out of proportion at this work rate.

Why is "Withdrawal of vagal tone to the airways" not the answer?

Changes in vagal tone do not explain this nonlinear rise.

Why is "A sudden fall in arterial PO2 detected by central chemoreceptors" not the answer?

Arterial PO2 remains near normal in exercise, and the central chemoreceptors respond to CO2 and CSF hydrogen ion.

What concept does this question test?

It tests Respiratory system: anaerobic threshold and ventilation in Physiology. The rise in hydrogen ion drives the peripheral chemoreceptors and ventilation climbs faster than oxygen uptake. Arterial PO2 and PCO2 stay close to normal during moderate exercise.

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 Respiratory system: anaerobic threshold and ventilation?

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.