Carbon dioxide exchange via the mucosa in healthy middle ear.

Abstract

Recent studies have shown that gas exchange via the middle ear mucosa, which is performed between the middle ear cleft and capillaries in the submucosal connective tissue, has an essential role in ventilation and pressure regulation in the middle ear cleft. We speculated that gas exchange via the mucosa is induced by the gas diffusion caused by the partial pressure gradient of gas between the middle ear cleft and submucosal capillaries. To evaluate the capacity of the gas exchange via the mucosa in the healthy middle ear of humans by examining the effect of the respiratory mode on middle ear pressure. We selected 13 volunteers ranging in age from 25 to 44 years with healthy ear drums and type A tympanograms. Middle ear pressure was measured in 1 ear of each subject every 2 minutes using tympanometry while the respiratory mode was altered, with the subject in the supine position. The partial pressure of carbon dioxide in the venous blood (PvCO2) and middle ear pressure were decreased by hyperventilation and increased by hypoventilation. The partial pressure of oxygen in the venous blood showed little change. Carbon dioxide diffused into the blood from the middle ear cleft in accord with the partial pressure gradient when the PvCO2 was reduced by hyperventilation, resulting in a decrease of middle ear pressure, whereas CO2 diffused into the middle ear cleft when the PvCO2 was elevated by hypoventilation, resulting in an increase of middle ear pressure. These findings suggest that a bidirectional CO2 exchange via the middle ear mucosa functions in the normal human middle ear.