The primary stimulus that drives respiration under normal resting conditions is:

• A Decreased arterial PO2
• B Decreased venous oxygen saturation
• C Carotid body stimulation by hypoxia
• D Increased arterial PCO2 and H+ concentration ✓

Explanation

Under normal resting conditions, the central chemoreceptors in the medulla are the dominant drivers of ventilation. They respond to increases in CO2 (which freely diffuses across the blood-brain barrier) and the resulting rise in CSF H+ concentration. Peripheral chemoreceptors (carotid and aortic bodies) primarily respond to hypoxia, hypercarbia, and acidemia, but their contribution is secondary under normal resting PO2 levels above 60 mmHg.

Reference: Guyton & Hall, Textbook of Medical Physiology, 14th ed.

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