Ventilation and clearance of the middle ear

Objective: To investigate the ventilation and drainage mechanism of the middle ear. Study design: Prospective. Setting: We observed 304 (of 337) middle ears with tympanic membrane perforation or myringotomy (102 normal, 90 with otitis media with effusion and 112 with chronic otitis media); 912 observations were recorded overall. Perforations were covered with solution, creating a fluid film, and inspected for gas bubbling at rest, and for outward and inward movement of the fluid film during swallowing. We also noted the inflammatory condition of the ear (i.e. dry, wet or purulent) and the perforation size. Results: Ears sometimes reacted differently in various sessions. Due to these differences, reactions were classified as 'types' of reactions rather than 'ears'. We refer to 449 'types' of 304 ears. Spontaneous gas bubbling at rest (indicating gas production) was observed in 98 per cent of normal types, 68 per cent of otitis media with effusion types and 65 per cent of chronic otitis media types. Evacuation towards the eustachian tube was observed in 47 per cent. no movement in 46 per cent and outward movement in 9 per cent. During swallowing, inward movement of the fluid film was observed in 74 per cent of normal types, 41 per cent of otitis media with effusion types and 32 per cent of chronic otitis media types. Conclusions: We found no support for the theory that the eustachian tube supplies air to the middle ear during swallowing. The normal middle ear produces gas which is evacuated by the Eustachian tube. In ears with otitis media, this mechanism appears to be impaired.