Gas composition of the normal and the ventilated middle ear cavity.

Epidemiologic and controlled studies indicate that late minimal hearing impairment is a sequelae after the use of a ventilation tube in early childhood. The patho-physiology is unknown, but abnormal middle ear gas composition might be important. Therefore it is mandatory to measure middle ear gas composition in order to understand the gas exchange in the normal middle ear, as well as the change in gas composition associated with ventilation tubes.Accordingly, the aim of this study was to measure middle ear gas composition both in the physiologic state and in artificial ventilation by a transtympanic tube. Employing puncture of the typanic membrane, through a liquid seal, we aspirated 300 microliters of middle ear gas. The procedure was carried out under the otomicroscope on adults without any anaesthesia. A total of 58 normals participated, along with 10 persons with unilateral ventilation tubes and 1 with a patent Eustachian tube.The mean values of physiologic state were: Partial pressure of oxygen in th...