Under normal resting conditions, the single most important chemical stimulus regulating ventilation is:

• A Arterial PO2
• B Arterial PCO2 ✓
• C Arterial pH alone
• D Plasma bicarbonate

Explanation

Arterial PCO2 — acting via H+ on the central chemoreceptors of the medulla — is the most important minute-to-minute regulator of ventilation in health. The hypoxic drive (via peripheral chemoreceptors) becomes important only when PaO2 falls below about 60 mmHg.

Reference: Ganong's Review of Medical Physiology, 26th ed.

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