Morning pressure in the middle ear.

Tympanograms were taken in the early morning in 25 persons with healthy ears. A first tympanogram was obtained shortly after waking up while the subject was still recumbent, and a second tympanogram was taken in the upright position after chewing and swallowing. Positive middle-ear pressure was found in a majority of ears, and the pressure was reduced after swallowing. The present results indicate that gas absorption from the middle ear is not important in quantitative terms during sleep. Otherwise the morning pressure would be expected to be negative. Two other experiments showed that the middle-ear pressure increased during shallow "sleep-type" breathing, and decreased during hyperventilation. The present results can be explained by diffusion of carbon dioxide over the middle-ear mucosa, the direction of gas transfer being dependent on the breathing pattern.