Tympanograms of otitis media with effusion: an experimental study

A sufficient explanation concerning tympanogram (TG) of otitis media with effusion (OME) has not been reported. The purpose of the present study was to investigate the relationship between the types of TG and actual pathological status of the middle ear system by means of experimentally modified middle ear clefts. In the present experiments, human temporal bones, guinea pigs' bullae and plastic models were used. The results were as follows: (1) Water was gradually poured into the middle ear cleft through the Eustachian tube. When the water level rose above the umbo, the height of TG slightly exceeded that of the original TG. Further addition of water produced M-shaped TG, however, flat TG (type B) was not detected until the water-line nearly reached the aditus. A similar phenomenon was observed in the plastic models when the water level reached the aditus-equivalent-site. (2) Tympanometrically measured middle ear pressure (MEP) was almost equivalent to the actual MEP recorded by a manometer when the tympanic membrane was normal. However, this result could not be duplicated in flaccid or adhesive tympanic membrane cases. (3) A clear reduction in the height of TG in guinea pigs' bullae was observed with decreased air volume. In addition, shallow TG was produced by an occlusion of the aditus of the human temporal bones and of the aditus-equivalent-site of the plastic models. It was demonstrated that the TG pattern depends on the fluid volume and location, air volume of mastoid cavity, intratympanic pressure and eardrum condition.(ABSTRACT TRUNCATED AT 250 WORDS)