Effects of cochlear hypoxia on otoacoustic emissions compared with auditory evoked potentials

The purpose of this study was to investigate the effects of mild systemic hypoxia on inner haircell (IHC) and outer haircell (OHC) function. A number of studies have explored the effects of anoxia/hypoxia and ischemia of the inner ear [e.g. 1,2,3,4,5] but have not addressed whether there is a dissociation between IHC and OHC function during such an insult. To monitor OHC activity we recorded otoacoustic emissions (OAEs) which are known to originate at OHC level. IHC/cochlear afferent nerve function was assessed indirectly from auditory brainstem evoked responses (ABR). We hypothesize that in chronic cochlear hypoxia, IHC (and cochlear afferent nerve) activity deteriorates before that of OHCs. Our study represents a model for effects of perinatal hypoxia or anoxia on the inner ears of high risk neonates which may be a contributing factor to the hearing deficits seen in auditory neuropathy [6,7]. We show that changes in IHC and OHC function during mild hypoxia occur with different time courses.