Why Do We Exhale Carbon Dioxide?

Humans exhale carbon dioxide because it is a waste product of cellular respiration. Too much carbon dioxide in the blood causes a condition called acidosis, which lowers blood pH.

When a person inhales, his diaphragm contracts, allowing the lungs to expand. The capillaries also move carbon dioxide into the air sacs. During exhalation, the diaphragm expands, reducing the size of the chest cavity. This forces air rich in carbon dioxide to exit the body via the nose and mouth.

The kidneys and respiratory system are responsible for removing excess carbon dioxide from the blood. Metabolic acidosis occurs when the kidneys cannot maintain a normal concentration of carbon dioxide in the body. Respiratory acidosis develops if the lungs cannot eliminate excess carbon dioxide. Respiratory acidosis sometimes occurs in people with chest injuries, obesity, chronic respiratory problems and problems with the nervous system.

Respiratory acidosis causes confusion, fatigue, sleepiness and shortness of breath, while metabolic acidosis causes headache, loss of appetite, rapid breathing and fatigue. In some cases, metabolic acidosis also causes a person's breath to take on a fruity odor. This typically occurs when someone develops diabetic ketoacidosis.

The treatment for acidosis depends on its cause. Doctors use oxygen therapy and medications to treat respiratory acidosis. If acidosis is caused by kidney failure, sodium citrate is one of the available treatments.