INFLUENCE OF AGING ON ACTIVE COCHLEAR MICROMECHANICAL PROPERTIES AND ON THE MEDIAL OLIVOCOCHLEAR SYSTEM IN HUMANS

Transiently evoked otoacoustic emissions (TEOAEs) without and with contralateral acoustic stimulation (CAS), as well as distortion product otoacoustic emissions (DPOAEs), were recorded on 60 subjects divided into 2 groups, the first constituted by 38 normally hearing young subjects and the second by 22 subjects aged from 70 to 88 years and with normal hearing levels in view of their age. TEOAEs and DPOAE 'audiograms' were recorded in a third group constituted by 15 subjects with ages ranging from 6 to 57 years and with hearing levels not significantly different from those of the second group for frequencies above 500 Hz. TEOAEs were present in 100% of the subjects in the first group and in 91% in the second group, although with smaller amplitude. The fall in TEOAE amplitude under CAS was smaller in the second group. Concerning DPOAE audiograms, in the first group, a response was found in 71 to 95% of cases for frequencies ranging from 1 to 6.35 kHz, and in 7 to 37% of cases in the second group. Mean amplitudes were significantly lower in the second group for frequencies ranging from 2.83 to 5.04 kHz. Mean 'thresholds' ranged from 38.55 to 43.57 dB SPL for frequencies ranging from 1 to 6 kHz in the first group and from 50 to 58 dB SPL in the second group. No significant difference was found between the second and third groups concerning the amplitude and spectrum of the TEOAEs and DPOAE audiograms. Thus, age influences TEOAEs, DPOAEs and the effect of CAS on TEOAEs. However, the alterations found in TEOAEs and DPOAEs seem to be essentially related to age linked hearing-loss.