Concepts on the pathogenesis of middle ear effusions.

Several concepts related to the pathogenesis of middle ear effusions are postulated. The mechanisms proposed are based on an understanding of fluid mechanics. A flask with a long, narrow neck is presented as a model of the Eustachian tube-middle ear-mastoid system. Fluid flow into and out of the flask is dependent upon the pressure gradient, compliance of the narrow neck and whether or not the bulbous portion is intact. It is suggested that locking of the tube may be dependent upon the speed of the application of the negative pressure and the compliance. Eustachian tube opening appears to be related not only to active muscle forces but may also be dependent upon the presence of a pressure gradient which passively assists tubal function. It is proposed that middle ear effusions result from reflux, aspiration or insufflation of nasopharyngeal secretions (acute otitis media), or from persistent functional or mechanical Eustachian tube obstruction (secretory otitis media) or both.