6 Control of respiration
Generally, respiration is an involuntary, automatic event. You are probably not aware it is happening unless you exert voluntary control over it by holding your breath, or breathing deeply. The rate and depth of your respiration adjusts automatically according to the metabolic needs of the tissues in the body. For example, athletes will breathe much more quickly and deeply during bouts of exercise to accommodate increased aerobic activity of their muscles, as discussed from 2:13 onwards in this video about Olympic rowing. (Make sure to open the link in a new window/tab so you can easily navigate back to this page.)
How does the body sense and respond to changes in metabolic rate? This function is mediated by peripheral chemoreceptors in the blood vessels and heart, and central chemoreceptors in the brain that detect changes in O2 and CO2 levels in the blood. Although changes in the partial pressures of both gases are involved in the regulation of respiration, alteration in PCO2 is the principal driver of respiration rate in humans.