Effects of Aging Versus Noise Exposure on Auditory System in Individuals With Normal Audiometric Thresholds

The study aims at investigating the effect of aging and noise exposure on the auditory system using auditory brainstem responses (ABRs), distortion product otoacoustic emissions (DPOAEs), and contralateral suppression of OAEs (CSOAEs). The objective was to compare DPOAEs, CSOAEs, and ABR in aged and noise-exposed individuals with the normal, to find an indicator for early diagnosis of auditory damage.

Sixty adult male participants were divided into 3 groups. Group 1 included individuals not exposed to occupational noise and group 3 included individuals exposed to occupational noise who were <35 years of age. Group 2 consisted of individuals with an age range of 45-65 years without any occupational noise exposure. DPOAE fine structure was studied at 8 points per octave at different F2 frequencies. Transient evoked otoacoustic emissions (TEOAEs) were measured with and without contralateral broad band noise (BBN) at 30 dB SL (CSOAEs). ABR was recorded using click stimuli at different levels, from 90 dB nHL down to 50 dB nHL. The absolute amplitude and peak latencies for peaks I, III, and V; and the wave V/I amplitude ratio were analyzed.

In CSOAEs, group 1 showed greater contralateral suppression when compared to group 2 and group 3. The amplitude of ABR wave I and the wave V/I ratio showed a significant difference between the 3 groups, and there was a reduction in amplitude of wave I for groups 2 and 3.

The findings indicate that the functioning of the auditory system is affected by occupational noise exposure and aging. CSOAEs, ABR wave I amplitude, and wave V/I amplitude ratio serve as reliable markers in the identification of hidden hearing loss.