Acoustic-distortion products: separation of sensory from neural dysfunction in sensorineural hearing loss in human beings and rabbits.

Because distortion-product otoacoustic emissions (DPOAEs) provide a noninvasive measure of outer hair-cell (OHC) activity, they should provide a unique and sensitive indicator of the effects of agents that damage hearing. Using DPOAE methods, the present study was designed to assess the relative contributions of the cochlea's outer hair cells to some common sensorineural diseases, including Meniere's disease, acoustic neuroma, and noise-induced, hereditary, and sudden idiopathic sensorineural hearing loss. Parallel evaluations of DPOAEs were performed under essentially identical conditions in rabbit models of several of the human disorders, including noise-induced hearing loss, endolymphatic hydrops, and cochlear neurectomy. Animal studies were performed to assess the proficiency of DPOAEs to track a developing sensorineural deficit as well as to compare patterns of DPOAE dysfunction between clinical and experimental forms of peripheral hearing loss. Detailed measures of DPOAEs were collected in the stimulus-frequency and intensity domains as "audiograms" and response/growth or input/output functions, respectively. The outcome of analyses of both human beings and animals supported the notion that DPOAE testing is sensitive to sensory-cell disease. Thus, in combination with conventional audiometry, DPOAE measures permit a distinction between the relative contribution sensory and neural components of the cochlea make to hearing deficits.