Preconditioning by the inhalation of pure oxygen protects rat’s cochlear function against noise-induced hearing loss

Background: Occupational noise-induced hearing loss (ONIHL) is a hearing disorder that affects workers all over the world. Preconditioning with several mild or less potent stressors will effectively prevent the development of noise-induced hearing loss. This study investigated the possible preventive effects of normobaric hyperoxia preconditioning on preventing the noise-induced hearing impairment in the rats. Materials and Methods: Four groups of male Wistar rats served as controls, exposed to normobaric oxygen, noise, or oxygen plus noise. The noise exposure lasted for 6 hours/day, 5 days/week, 4 weeks and the preconditioning conducted by inhalation of pure oxygen (95%) for 3 hours/day, 6 days/week, 1 week in a chamber prior to noise exposure. A bandpass noise of 100dB SPL centered at 8 KHz was used for noise exposure. Click and tone burst auditory brainstem responses (ABR) and distortion product otoacoustic emissions (DPOAE) audiograms were recorded in order to evaluate the level of hearing loss among the subjects before the beginning and 4 weeks post-exposure. Statistical analysis was performed using SPSS. Results: The weekly pre-conditioning by normobaric hyperoxia significantly reduced the ABR threshold shifts and restored the amplitudes of DPOAE (P < 0.001). The control group did not show any difference in terms of DPOAE and ABR tests during and after the exposure (P > 0.050). Conclusions: The preconditioning successfully protected the rats&rsquo; hearing by maximizing and developing tolerance to ischemia and hypoxia caused by the noise. The application of such preconditioning is then considered as a possible complementary preventive solution.