What physiological condition results in excessive loss of carbon dioxide from the blood?

Hypocapnia is the physiological condition characterized by an abnormally low concentration of carbon dioxide (CO2) in the blood. This condition typically arises due to hyperventilation, where excessive breathing leads to an increased expulsion of CO2, thereby reducing its levels in the bloodstream.

When carbon dioxide levels fall, the body's acid-base balance is also affected. CO2 is a critical component in maintaining normal blood pH; thus, a significant decrease in CO2 levels can lead to respiratory alkalosis. This is primarily because CO2 plays a role in the bicarbonate buffering system that regulates acidity in the body.

In contrast, hypoxemia refers to low oxygen levels in the blood, while hypercapnia indicates excess carbon dioxide, which leads to respiratory acidosis. Acidosis itself describes an overall increase in acidity in the body fluids, which can occur due to various conditions, including respiratory failure or metabolic disturbances. Hence, hypocapnia specifically and directly relates to the excessive loss of carbon dioxide, echoing why it is the correct choice in this scenario.