[Comparison of methods for early detection of noise vulnerability of the inner ear. Amplitude reduction of otoacoustic emissions are most sensitive at submaximal noise impulse exposure].

Noise-induced temporary impairment of cochlear function was measured with several audiometric tests in order to evaluate which method best predicts a vulnerable cochlea. We tested 10 normally-hearing and 13 subjects who were positive for temporary threshold shifts (TTS). The latter were selected from 194 soldiers who demonstrated a TTS higher than 15 dB after regular training with firearms. Acoustic distortion products (DPOAE), click-evoked otoacoustic emissions (TEOAE), upper limit of hearing (ULH) and pure-tone and high-frequency audiometry were used to evaluate possible increased vulnerability of the cochlea. Tests were conducted at lower sound intensities (white noise, 90 dB SPL, 5 min; impact noise, 100 or 106 dB SPLs, 10 impulses/s, 5 min). Seventy per cent of the TTS-positive soldiers studied exhibited significant reductions of TEOAE amplitudes, whereas a stable emission was observed in all control subjects. DPOAE alterations were seen in 38% of the soldiers tested. These results indicate that TEOAE is the most sensitive, objective method for detecting a positive disturbance in cochlear function. Although the upper limit of hearing was also a very sensitive method, variability of this psychoacoustic method depended on the help and experience of the subjects being tested.