[Acoustic nerve adaptation in chronic acoustic trauma]

The adaptation phenomenon of the the cochlear nerve in the highest frequency region was studied by means of electrocochleography in the group of 32 persons exposed to prolonged noise and with noise-induced, mild hearing loss (in the 4--6 kHz region) and in 19 persons under the same conditions of noise-exposure but, without any evidence of the hearing loss. The same investigations were performed in the group of 27 normal-hearing persons and non-exposed to noise. In the whole group of persons exposed to prolonged noise, disregarding their hearing condition the amplitude-decrease of the action potential of the cochlear nerve due to the adaptation procedure, was twofold in comparison to the non-exposed persons. The latency of this potential was longer in the whole group of exposed to noise persons than in the intact persons. It was presumed that this type of auditory nerve adaptation results infinitial, ultrastructural noise-damage within the basal turn of the cochlea. Basing on the obtained results it was postulated that the adaptation phenomenon in the highest-frequency region can serve as an indicator of early noise-induced malfunction of the cochlea which probably precedes the highest-frequency threshold elevation in conventional audiometry.