[Effect of contralateral noise exposure on otoacoustic distortion product emissions in man].

The influence of contralateral white noise with levels of 50 and 60 dBnHL on the amplitude of distortion-product otoacoustic emissions (DPOAE) was measured. Thirty ears of normally hearing adults (17 women, 13 men, mean age 26.5 +/- 5.3 years) were examined. Two representative DPOAE frequencies 2f1-f2 = 1342 Hz and 6341 Hz were compared. The lower DPOAE frequency was placed in the frequency region where middle-ear pressure has a strong influence on DPOAE amplitudes, the higher DPOAE frequency respectively in the region where lesser influence is exerted by middle-ear pressure. During the application of contralateral white noise a statistically significant total of 85% of DPOAE amplitudes was reduced, although there was some variation in the individual behaviour of DPOAE amplitudes. In general the higher DPOAE frequency (6341 Hz) was reduced distinctly less than the lower DPOAE frequency (1342 Hz). The reaction of DPOAE amplitude depended closely on the time course of the contralateral stimulus and amplitude reductions were present over 10 minutes without adaptation or fatigue. It is not possible to differentiate between middle-ear or inner-ear mediate effects but the middle ear is at least involved. Based on the presence of those DPOAE amplitude reductions over ten minutes without adaptation or fatigue and the fact that lower frequencies are influenced much more than higher frequencies a synergistic effect--middle-ear and efferent mediated--is suggested.