Experimental studies have demonstrated that the partial pressure of carbon dioxide in blood rapidly equilibrates with the partial pressure of carbon dioxide in the alveolar space (Alveolar Carbon Dioxide
) early in its course through the pulmonary capillaries. In other words, the partial pressure gradient of carbon dioxide across the alveolar membrane is eliminated early on as blood moves through the pulmonary capillaries. Consequently, pulmonary gas exchange of carbon dioxide is perfusion-limited
. It appears that few physiological or pathological scenarios can change this perfusion-limited character of carbon dioxide transport and thus we do not discuss this topic further.