Abstract
The present paper was designed to study acoustic trauma, particularly C5-dip, audiologically;and histopathologically.An audiological analysis was performed on 49 persons with hearing loss of C5-dip. The method used was detailed audiometry, a new method for detailed measurement of hearing threshold along the frequency scale, in which very slow frequency sweep was adopted in ordinary Bekesy audiometry.On the other hand, the integrity of the organ of Corti after exposure to high intensity impulse noise was studied on guinea pigs with the use of surface preparation technique.Twenty-five guinea pigs were exposed to impulse noise at the intensity of 150 dB SPL, with irregular intervals of 2-3 sec, for 30 min. After exposure, with survival time of 7 days, materials were sacrificed for histological study of the organ of Corti.The results were as follows:1) Analyzing the detailed audiogram of C5-dip, it was observed that the hearing threshold declined suddenly at a certain point between 2 and 4 kHz, and reached the bottom of wide or narrow range and then recovered to a nearly normal level with very sharp slope. According to the width of the bottom, two different types of “dish” and “bowl” were distinguished principally.2) At the histological observation, hair cell damage of two different types, “notch” and “gradual”, were recognized.In the “notch” type, hair cell damage was sharply limited against the both sides of intact structures. In the “gradual” type, scattered damage area was observed between the normal and completely damaged area.3) It was suspected that functional disturbance and structural disturbance might be related each other: the “dish” type corresponded to the “notch” type, and the “bowl” type coincided with the “gradual” type
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