Distortion product emissions in humans. III. Influence of sensorineural hearing loss.

The realization that otoacoustic emissions are sensitive to cochlear disorders has resulted in the speculation that they may have considerable clinical potential as objective measures of hearing. To assess the clinical utility of one type of emission, the distortion product emission (DPE), a study was undertaken in individuals with hearing impairments representing a number of common otologic disorders. The results of this investigation provided evidence that tests of DPEs promise to satisfy a number of requirements important to clinical testing, including objectivity of measurement procedures, test-retest reliability, simple subject preparation, readily available instrumentation, and relatively brief examination periods. The fine resolution of DPEs within the stimulus frequency and level domains also permits an accurate confirmation of the pattern of hearing loss. For example, tests of DPEs detected a 20-dB hearing level impairment at a single frequency in an ear exhibiting early signs of noise-induced hearing loss, and a 10-dB improvement in sensitivity following ingestion of the hyperosmotic agent glycerol in an ear displaying a mild to moderate hearing loss due to Meniere's disease. Finally, the application of DPEs to the objective testing of otologic disorders suggests that the ability of these responses to assess the sensory component of a sensorineural disorder may contribute to the eventual understanding of the complicated pathogenesis of many cochlear diseases. When all the positive features of DPE testing are realized, the potential contribution that these measures can make in a clinical setting becomes apparent.