Middle-ear pressure under basal conditions.

Spontaneous pressure changes in the middle ear were measured under basal conditions in ten subjects with healthy ears. A special "zero sweep rate" tympanometric procedure was developed in order to improve the accuracy of measurement. The respiratory carbon dioxide tension was recorded, and swallowings were indicated automatically. Results showed that the pressure in the majority of ears remained slightly above the atmospheric pressure. In some ears, the pressure increased during periods of drowsiness or sleep when the end-expiratory carbon dioxide tension was rising and the number of swallowings declined. In two ears, the middle-ear pressure showed a slow continuous increase during a two-hour observation period. The present results indicate that the gas turnover in the middle ear by diffusion shows a positive balance during basal conditions. Our findings thus speak against the common belief that the middle-ear gas is continuously being absorbed.