Primary Respiratory Drive: The Role of PaCO₂

The primary drive to breathe is the partial pressure of carbon dioxide in arterial blood (PaCO₂). Central chemoreceptors in the medulla respond to CSF pH changes caused by CO₂ diffusion across the blood-brain barrier. Rising PaCO₂ → increased ventilation; falling PaCO₂ → decreased ventilation.

Peripheral chemoreceptors (carotid/aortic bodies) respond primarily to hypoxemia (low PaO₂) and acidosis, serving as a secondary/backup drive.