Pressure Changes in the Middle Ear After Altering the Composition of Contained Gas

Abstract

Pressure changes have been examined in five middle ears after introduction of different gas mixtures containing approximately 100%, 55%, 21% and 10 % oxygen in nitrogen. The pressure changes were followed with an apparatus similar to van Dishoeck's pneumophone. With Eustachian tube closed the observed pressure fell at rates up to 23 cm H₂O/h. With intermittent introduction of air through the Eustachian tube, the rate of fall declined over periods up to 30 hours. The combined results showed a linear relation between the overall pressure drop (time integral of observed rates of pressure change) and percentage of oxygen in gas breathed, from which it is concluded that oxygen absorption was the main cause of observed pressure change. The results suggest roughly 55 mm Hg as the normal steady state partial pressure of oxygen in the middle ear.