Otoacoustic Emission in Noise-Exposed Normal Hearing Workers

Abstract

Objective: Otoacoustic emission test is useful in monitoring hearing changes and cochlear damage by noise still not detectable in pure-tone audiometry.The aim was to evaluate amplitude of the signal and signal/noise ratio of distortion product otoacoustic emissions (DPOAE) in normal hearing workers exposed to different noise doses.

Method: This is a cohort prospective study performed in metalworking industries, in 3 groups of normal hearing workers, GI not exposed (n = 50), GII sporadically exposed (n = 50), and GIII often exposed to occupational noise (n = 50). DPOAE were performed after 14 hours of hearing rest. “Pass-fail” criterion was employed for analyses.

Results: Six hundred eight workers underwent hearing thresholds, and 150 of them matched the inclusion criteria and had DPOAE recorded. DPOAE alterations in amplitude of signal and signal to noise ratio were found in groups II and III bilaterally, and the higher the frequency tested the lower were the results in GII and GIII (P < .05). The greater the exposure to noise dose the lower the results (P < .05). GI showed better results according to pass and fail criterion and higher amplitude of the signal and signal/noise ratio than GII and GIII (P < .05).

Conclusion: DPOAE results are worse in the exposed groups according to occupational noise dose. It is important to search for undetectable hearing changes in all workers exposed to occupational noise even sporadically, and to encourage the use of hearing protectors, in order to prevent possible irreversible damage.