What is the most important factor in the control of ventilation under normal conditions?

The most significant factor in the control of ventilation under normal conditions is the PCO2 of the arterial blood. Carbon dioxide levels play a critical role in the regulation of breathing because they are closely tied to the body’s metabolic activity and the need to maintain acid-base balance. When CO2 levels rise (hypercapnia), it leads to a decrease in blood pH, which stimulates chemoreceptors in the brain and blood vessels. This stimulation results in an increase in the rate and depth of respiration to expel the excess CO2, thus restoring homeostasis.

Even in conditions of varying oxygen availability, the body prioritizes the removal of CO2 because it is a potent respiratory stimulant. Oxygen levels (PO2) are also important, but their effect on ventilation is secondary to that of CO2 under normal physiological conditions. The body can tolerate fluctuations in oxygen levels more readily than it can tolerate increases in carbon dioxide, emphasizing the preeminence of arterial PCO2 in respiratory control.