Mechanisms in noise-induced permanent hearing loss: an evoked otoacoustic emission and auditory brainstem response study.
In this study 22 patients (44 ears) with noise-induced permanent hearing loss were audiologically evaluated using transient-evoked otoacoustic emissions (TEOAE) and auditory brain-stem response (ABR). Twenty-one normal subjects (42 ears) without exposure to occupational noise were used as controls. Based upon the hearing loss at 4, 3, 2 and 1 kHz on the pure-tone audiogram, they were classified into four groups. In group 1 (eight ears), emissions were present in all ears but their TEOAE-noise level and their reproducibility (percentage) proved to be weak. The auditory brain-stem response (ABR) indicated that the I/V amplitude ratio, the latency values of wave V and the I-V intervals fell within the normal range in all ears. In Group 2 (14 ears), 40 per cent had no emissions, whereas the remaining ears showed weak emissions. The ABR revealed that in all ears the I/V amplitude ratio became small while wave V peak latency as well as I-V intervals were within the normal range. In Group 3 (10 ears), emissions were absent in 50 per cent, while in the other ears the emissions were very weak. The ABR revealed that the I/V amplitude ratio, which could be calculated in the 60 per cent in which wave I was present, was smaller than in Group 2. Wave V latency as well as I-V intervals were within the normal range. In Group 4 (12 ears), none of the ears showed emissions. The ABR indicated that the I/V amplitude ratio was much smaller when wave I was present (27 per cent) as well as I-V interval values being within the normal range. Wave V absolute latency value (delta V index) indicated a positive index in 17 per cent of this group (two ears) when wave I was absent. In the present study a dynamic process from cochlear outer hair cells to cochlear neurons was seen, correlating with an increasing hearing loss.
Xu
Z M
ZM
Department of Otolaryngology, University Hospital Ghent, Belgium.
Vinck
B
B
De Vel
E
E
van Cauwenberge
P
P
D000328:Adult; D000375:Aging; D000704:Analysis of Variance; D001300:Audiometry, Evoked Response; D016022:Case-Control Studies; D003056:Cochlear Nerve / Q000473:pathology; D016057:Evoked Potentials, Auditory, Brain Stem; D018072:Hair Cells, Auditory, Outer / Q000473:pathology; D006317:Hearing Loss, Noise-Induced / Q000473:pathology / Q000503:physiopathology*; D006801:Humans; D008297:Male; D008875:Middle Aged