Diurnal fluctuations of middle ear pressures in atelectatic ears.

The tympanic membrane of 18 atelectatic ears was examined before and immediately after nocturnal sleep. On the patients' awakening, eight (44.4%) of these ears presented a spontaneous disappearance of the atelectasis. The original atelectatic state reappeared thereafter within 75 min (on average). This time corresponds to diffusion into the circulation of a gas mixture similar to air. The spontaneous autoinflation of atelectatic ears cannot therefore be explained by nocturnal CO2 diffusion into the middle ear, as CO2 would rediffuse in a matter of 5 min. Nocturnal relaxation of the Eustachian tube muscles with opening of the tube and influx of air into the middle ear is the suggested mechanism which may be at the root of the phenomenon described in this study. The phenomenon itself emphasizes the fluctuating nature of atelectatic conditions, and raises questions regarding the cardinal role played by swallowing in aerating the middle ear.