Occupational exposure to noise decreases otoacoustic emission efferent suppression

With the discovery of otoacoustic emissions (OAEs), the efferent cochlear system has become accessible for investigation in humans. Recently, it has been suggested that contralateral sound activated OAE efferent suppression may provide an early indication of auditory damage due to exposure to noise. In this study, OAE efferent suppression in normally hearing subjects, occupationally exposed to noise, was compared with respective effects in healthy, non-exposed subjects. The noise-exposed group exhibited higher mean hearing thresholds at frequencies 4, 6 and 10 kHz (p < 0.01) and lower-level transient-evoked otoacoustic emission (TEOAE) and distortion-product otoacoustic emission (DPOAE) at a frequency of 4 kHz (not significant). TEOAE efferent suppression was moderately decreased, whereas DPOAE efferent suppression was negligible, in the exposed group compared to non-exposed subjects. The results of the study suggest that OAEs, particularly DPOAE contralateral suppression, are likely to become a valuable method for assessing early hearing damage caused by exposure to noise.