How is blood chemistry related to ventilation?

Answer 1

Ventilation is controlled by certain centers in the brain stem that monitor the pH of the blood.

The pH is usually a result of the amount of carbonic acid in the present in the blood. Carbonic acid is the 'transportable' form of CO2. Therefore, if the pH is too low, the body thinks it needs to get rid of carbon dioxide and does so by increasing ventilation which allows CO2 to be "blown off". Furthermore, if the pH gets too high, ventilation will be suppresses to allow carbonic acid to "build up" to decrease the pH.

However, the pH can be changed by other acid/basic chemical accumulations/deficiencies in the blood, and the same ventilation responses result. For example, even if the carbonic acid level is NORMAL, if there is an increase inlactic acid, the blood pH will decrease. This will cause ventilation to increase to blow off some carbonic acid (even though the carbonic acid is normal) to try to raise pH back to normal.

Therefore, we know that although breathing is INDIRECTLY related to CO2 levels MOST OF THE TIME, it is ALWAYS DIRECTLY related to pH levels, and decreased pH causes increased ventilation, while increased pH causes decreased ventilation.