Sensitive detection of noise-induced damage in human subjects using transiently evoked otoacoustic emissions

Thirty-eight males (76 ears) exposed to occupational noise were investigated using transient-evoked otoacoustic emissions. Based upon the hearing loss at 4 kHz, they were classified into four described groups. Ten normally hearing subjects (20 ears) without exposure to occupational noise were used as controls. Significant changes in response amplitude, reproducibility, and signal to noise ratio (SNR) in broadband and frequency-bands (1, 2, 3, 4 kHz) were revealed between control subjects and the patients of group I exposed to noise with normal pure-tone audiometric thresholds. The changes of response amplitudes, reproducibility (%), and SNR were not significant between the group I and the patients of group II with mild hearing loss (< or = 40 dB) at 4 kHz. When the patients suffered from hearing loss beyond 40 dB HL at 4 kHz, emission amplitude, reproducibility, and SNR showed significant changes, whereas the percentage of absent emissions also showed significant changes. From these data, we conclude that TEOAE testing is more sensitive than pure-tone audiometry in the detection of early noise-induced damage. The test could be proposed as a hearing screen for monitoring employees with early noise-induced hearing loss.