When athletes exercise, what is the primary physiological variable responsible for their sustained increase in ventilation rate?

The right answer is Increased pCO2.

Respiratory acidosis is a disorder of blood pH regulation. The cause of this disorder is respiratory, it occurs in case of hypoventilation or hypoxia. During prolonged apnea, we speak of hypercapnia. Respiratory acidosis is one of two acidosis, the other being metabolic acidosis.

The concentration of CO2 in the blood increases; this gas is then converted by chemical reaction: CO2 + H2O = H+ + HCO3-, which causes a drop in blood pH. He becomes pathological.

During respiratory acidosis, the patient hyperventilate, in order to lower his CO2 level in the blood. However, when the cause of hypoventilation is related to any hyperventilation impossibility, the body will regulate its blood pH by increasing its concentration of bicarbonates HCO3- in the blood.

This regulation (metabolic compensation) is done first at the liver, which favors nitrogen excretion in the form of glutamine, rather than in the form of urea. This allows the body to eliminate less bicarbonates, which leads to an increase in their concentration and therefore, by shifting the equilibrium, a rise in pH.