Background: Noise induced hearing loss (NIHL) is one of the most important occupational diseases worldwide. NIHL has been found to be potentiated by some of air pollutants. Exposure to noise plus carbon monoxide is common in occupational and environmental settings. This study was performed to evaluate the effect of noise and carbon monoxide exposure simultaneously on rabbits' hearing system by Auditory Brain stem Response (ABR) assessment.

Materials and Methods: In this experimental study, 24 male adult white rabbits were divided to four groups: control group, noise exposure group, noise plus carbon monoxide exposure group and carbon monoxide exposure group. Auditory Brain stem Responses of the four groups were determined: before exposure, 1 hour after exposure and 14 days after exposure by click and tone burst stimulus.

Results: The latency mean time of V wave in the ABR test for the group exposed to noise plus carbon monoxide, 1 hour after exposure at 1, 2, 4 and 8 KHz frequency were respectively 5.43±0.08, 5.50±0.07, 5.71±0.07 and 5.75±0.07 millisecond. These values were significantly more than the same values in the other groups.

Conclusion: NIHL may be potentiated by carbon monoxide in the simultaneous exposure. Thus, it seems occupational and environmental exposure to noise plus carbon monoxide may increases hearing loss risk.