Effect of ageing on otoacoustic emissions and efferent suppression in humans.

Transiently evoked otoacoustic emissions (TEOAEs) without and with contralateral acoustical stimulation, were recorded on 52 subjects ranging from 20 to 78 years. Subject selection was based on the hearing levels from 0.5 to 4 kHz being better than 25 dB HL, normal tympanograms and stapedial reflexes, presence of TEOAEs in at least one ear and no history of otological disease, noise exposure, ototoxic drugs, metabolic disease associated with hearing loss or a family history of hearing loss. The ear with better audiological thresholds was selected as the test ear. If there was no difference between the ears, the ear with stronger TEOAEs was selected. Subjects were divided into five age groups: 20-34 years (n=12, mean age 23.7), 35-44 (n=11, mean age 39.7), 45-54 (n=8, mean age 48.1), 55-64 (n=10, mean age 60), 65-78 (n=11, mean age 71). TEOAEs were never absent in the first two groups, but they were absent in two ears in the 45-54 group, and in one ear of the 55-64 and 65-78 groups. Mean TEOAE amplitude decreased with age, but the differences between the five groups were not significant. Contralateral white noise suppressed emission amplitude, but the amount of suppression was not significantly different between the five groups. A linear regression analysis showed a significant correlation between age and hearing levels, and a negative correlation between age and TEOAE amplitude. In addition, a significant negative correlation between hearing threshold and TEOAE amplitude was evident. No effect of age on the amplitude of the efferent suppression was found.