Effects of Noise Exposure on Hearing in Industrial Workers: Comparing the Findings between Pure Tone Audiometry and Otoacoustic Emission

Background and purpose: Stimulus-evoked otoacoustic emission (OAE) is generated by the outer hair cells (OHCs) and high levels of noise will highly damage these cells. Therefore, even a mild loss in OHCs could alter the generation of OAE. The aim of this study was to assess and compare the pure tone threshold, Distortion Product Otoacoustic Emission (DPOAE) amplitude in industrial workers experiencing non-permissible noises and administrative staff. Material and methods: This descriptive cross-sectional study included 134 workers who were exposed to non-permissible noise and a control group consisting of 89 administrative staff. The threshold of pure tone and DPOAE amplitude were assessed and recorded. Results: The mean of pure tone threshold was high in 1,2,3 and 4 KHz in workers compared to that of the administrative staff. There was a significant difference in the mean of pure tone threshold in 3 and 4 KHz (P<0.01). DPOAE amplitude for 4 frequency (1.4, 2.2, 2.9, and 4.4 KHz) was greater in control group, however, this difference was significant only in 4.4 KHz (P<0.01). Conclusion: The decrease of OAE amplitude and increase in audiometric threshold in workers exposed to noise indicates damage to cochlea. DPOAE may closely match with audiometric results since there is frequency sensitivity in DPOAE amplitude due to noise-induced hearing loss.