Effect of noise exposure on auditory system of industrial workers using pure tone audiometry (PTA), transient evoked otoacoustic emissions (TEOAEs) and distortion product otoacoustic emissions (DPOAEs)

Different studies have shown that Otoacoustic Emission (OAEs) is generated by Outer Hair Cells (OHCs) and these sensory cells are first structures exposed to damage of high level noise. Therefore minor impairment in OHCs can lead to lack of response of OAE. The purpose of the current study is to compare the pure tone thresholds، Transient Evoked Otoacoustic Emission (TEOAE) and Distortion Product Otoacoustic Emission (DPOAE) amplitude in industrial workers experiencing non-permissible noises and official staffs. This study was conducted as a case control paradigm. The cases included 134 workers exposed to non-permissible noise and control group that constituted 89 official staff. The threshold of pure tone، TEOAE and DPOAE amplitudes were recorded and compared among the subjects. Pure tone thresholds at frequencies of 1- 4 KHz among industrial workers were higher (worse) than the control group and these differences were significant within frequencies of 3 and 4 KHz (p< 0. 01). TEOAE amplitudes within 4 frequencies (1-4 KHz) indicated significant decrease among workers group in comparison with control group (p<0. 05). Although DPOAE amplitudes indicated decrease within 4 frequencies in the workers group، these differences were statistically significant only in 4. 4 KHz (p< 0. 01). The decrease of OAE amplitudes and increase in audiometric thresholds in workers may indicate damage to cochlea due to noise exposure. In the current study، the sensitivity and specificity of DPOAE frequency responses was estimated higher than the TEOAE. It seems that DPOAE responses may have been more homogeneic to audiometric results.