Influence of a 6-8 kHz audiometric notch on transient evoked otoacoustic emissions

Thirty-eight patients with known unilateral cochlear hearing loss at 6 and/or 8 kHz were examined for transient evoked otoacoustic emissions (TEOAEs). These findings were compared with those of the contralateral "normal hearing" ear. Statistically significant lower values of echo reproducibility and amplitude were recorded in hearing-impaired ears, together with a more narrow TEOAE spectrum. In addition to these findings, a globally reduced amplitude of the cochlear response was found that was unrelated to the frequency impaired in pure-tone audiometry (6, 8, or 6-8 kHz). Since patients' audiometric thresholds at such frequencies could influence test results, findings could possibly be due to an altered echo travelling wave across the most basal part of the cochlea or to coexisting damage in the rest of Corti's organ that were undetectable with standard audiometry. A significant overlap was found between the results from hearing-impaired ears and those from normally hearing ones. Although TEOAEs were not helpful in the present study in identifying patients with a unilateral hearing loss at 6 and/or 8 kHz when compared to normal contralateral ears, they are still considered to play an important role in the follow-up of subjects at risk for hearing damage.