[Transmission of changes in the external ear atmospheric pressure to the perilymph].

Using guinea pig, pressures in the external ear canal, in the middle ear and in the perilymph were registered simultaneously, while pressure was applied to the external ear canal using an impedance audiometer. In the first experiment, applied pressure was changed in the range from 200 mmH2O to -200 mmH2O with and without the opening of the otic bulla. The change in the perilymphatic pressure with the opening was smaller than that without the opening. The result indicates that the external ear pressure is transmitted to the perilymph not only via the ossicular chain but also via the middle ear cavity without the opening, while it is exclusively transmitted via the ossicular chain with the opening. Pressure transmission to the perilymph was significantly impaired either by disrupting the ossicular chain or by closing the round window niche, especially by the latter. Thus the middle ear cavity itself plays an important role in pressure transmission from the external ear canal to the perilymph mainly via the round window. In the second experiment, applied pressure to the external ear canal was changed in the range from 1000 mmH2O to -1000 mmH2O after the Eustachian tube being closed. Between 400 mmH2O and -200 mmH2O, the middle ear and perilymphatic pressures paralleled well with the applied pressure. Beyond these levels, the middle ear pressure increased or decreased in response to the applied pressure but the perilymphatic pressure reversed against the middle ear pressure. Communication between perilymph and cerebrospinal fluid via the cochlear aqueduct is thought to be a major factor causing this reversal which, in turn, aggravates pressure gradient between the middle ear and the perilymph.(ABSTRACT TRUNCATED AT 250 WORDS)