Why is it so important to maintain Alveolar ventilation rate for a given metabolic rate?

Answer 1

As metabolic rate increases, more oxygen is used and more carbon dioxide is produced. Thus, alveolar ventilation needs to increase with increased metabolic rate so that enough oxygen is taken into the body to meet the needs. Alveolar ventilation also directly affects the acid/base balance of the body. When a person holds their breath, carbon dioxide (a by product of normal cell metabolism) builds up in the blood. There is an enzyme, carbonic anhydrase, that speeds up the combination of carbon dioxide and water (from the blood plasma) into carbonic acid. This weak acid readily dissociates in water (i.e., the blood plasma) into bicarbonate and hydrogen ion. Since pH is defined as the negative log of the hydrogen ion concentration ion, as H+ increases, the pH decreases.
The opposite reaction occurs during hyperventilation. Hyperventilation is defined as an increase in the amount of fresh air in the alveoli per unit time. While very little extra oxygen is taken in (because the blood is approximately 98% saturated with oxygen during normal breathing), much more carbon dioxide is blown off than usual. Thus, the equation is driven in the opposite direction, and H+ ions are removed from the blood, causing an increase in the pH.