[dillydogg]

The acid base balance of the cerebrospinal fluid is the primary driver of the respiratory drive, like allude to with your comment on the CO2. I did want to add that the lack of oxygen can affect respiration, which is detected by the peripheral chemoreceptors, like in the carotid bodies.

Additionally, the thoracic stretch receptors are important for respiratory drive, where the lack of expansion of the chest will promote respiration. When a healthy young person holds their breath for short periods, say 30 seconds or so, their blood CO2 and O2 are not much different, but they still will have to fight the instinct to breathe!