Effect of hypoxia on noise-induced auditory impairment

Chemical asphyxiants have been shown to potentiate noise-induced hearing loss (NIHL) in our previous reports. However, it is still unclear whether hypoxia interacts with noise to potentiate NIHL. This is an important issue, since many people at risk of exposure to noise may also suffer from hypoxia. In the present study, rats were exposed to 14.1-kHz octave-band noise at 105, 110, and 115 dB SPL and hypoxic air (10% O₂ and 18% O₂) for 4 h. Cochlear compound action potential threshold loss and hair cell loss were determined 4 weeks after the exposure. Though the hypoxia did not cause hearing loss and hair cell loss, the combined exposure to noise and hypoxic air caused more hearing loss and hair cell loss than the noise alone. The NIHL potentiation by hypoxia appeared to increase linearly with the hypoxia level. 10% O₂ exposure significantly potentiated NIHL and 18% O₂ exposure also showed an evident NIHL potentiation. This suggests that people suffering from hypoxia may have increased risk to noise trauma.