Effect of different exposure times to compliance noise on rabbits’ hearing protection by distortion product oto acoustic emissions

  Background: Excessive noise is known as the most physical harmful factor in the industrial societies. There are several hearing protection methods against noise. Compliance with noise is attributed as one of the protection mechanisms of auditory system.   Objective: This aim of this study was to determine the effect of different exposures time to compliance noise on rabbit's hearing protection by Distortion Product Oto Acoustic Emissions (DPOAEs).   Methods: This experimental study was carried out on 25 male three-months-old New Zealand white rabbits in five groups including group 1 as trauma group exposed to 105 dB SPL at 500-3000 Hz for 8 hours per day in ten days groups 2, 3, and 4 as compliance noise groups with daily exposure to 80 dB SPL compliance noise at 500 to 3000 Hz for 1, 2 or 4 hours before exposure to 105 dB trauma noise in ten days and group 5 as control group. All rabbits were anesthetized for DPOAE measurement before any exposure and post-DPOAE measurement (16-20 hours following final exposure). Data were analyzed by ANOVA, TUKEY and DUNNET tests.   Findings: Mean DPOAE response differences of right ear in groups 2, 3 and 4 (compliance groups) were much lower than group 1 (noise trauma group). No significant differences were observed between mean DPOAE response amplitudes at low and middle frequencies in right ear of groups 3 or 4 and control group. Differences between mean DPOAE response levels in trauma group compared to control group were statistically significant (P<0.05).   Conclusion: Lack of significant differences between mean DPOAE responses of compliance and control groups suggests protective effect of compliance noise on hearing health before exposure to noise trauma.