Evaluation of noise induced permanent hearing loss : an evoked otoacoustic emission and auditory brain stem response study

Abstract EN

This study was done to identify the site of the pathologic process in noise-induced permanent hearing loss using Transient Evoked Otoacoustic Emission (TEOAE) and Auditory Brain Stem Response (ABR).

Twenty-five patients (50 ears) with noise-induced permanent hearing loss were audiologically evaluated using TEOAE and ABR.

Twenty-two normal subjects (44 ears) without exposure to occupational noise were used as controls.

Based upon the pure tone hearing loss at 4,3,2 and 1 KHz, patients were classified into four groups [subgroup (1), hearing loss started at 4 kHz, subgroup (2), hearing loss at 4 and 3 kHz, subgroup (3) hearing loss at 4, 3 and 2 kHz and subgroup (4) hearing loss at 4, 3, 2 and 1 kHz].

TEOAE noise level and their reproducibility (percentage) proved to be weak and detected in all patients of group I.

It was not detected in 40%, 60% and 100% in group II, III and IV respectively.

TEOAE has a negative correlation with noise-induced permanent hearing loss.

The 1-V intervals of ABR were within normal range in the four groups.

The I/V amplitude ratio was within normal range in group 1, then it became small in all patients of group II, in-group III it became smaller as wave 1 was calculated in 60%.

In group TV the I/V amplitude became much smaller as wave 1 was calculated in 27% of patients.

The wave V latency was within normal range in the first three groups.

In group IV wave V absolute latency value (AV index) indicated a positive index in 28% (4 ears) when wave I was absent.

Wave 1 latency and I/V amplitude ratios of 'ABR were affected in noise-induced permanent hearing loss patient.

From the present study it was conclude that a progressive damage from cochlear outer hair cells to cochlear neurons occurred correlating with an increasing noise-induced permanent hearing loss.