Hiroyasu Mashino

Age-related changes in evoked otoacoustic emission in normal-hearing ears.

The evoked otoacoustic emissions (e-OAEs) elicited by both tone-bursts and clicks were investigated in normal-hearing ears of three age groups: young age group (approximately 30 years), middle age group (31-50 years) and old age group (51 years approximately). The pseudothreshold of tone-burst e-OAE at stimulus frequencies between 500 Hz and 2 kHz was significantly elevated in the middle and old age groups compared with that in the young age group. When the relationship between averaged emission cochleograms drawn from the mean pseudothresholds of tone-burst e-OAEs at 6 stimulus frequencies between 500 Hz and 4 kHz and averaged pure-tone audiograms was analyzed, a clear difference was found among the three age groups in a frequency range between 500 Hz and 2 kHz. Total echo power, reproducibility, highest peak power and frequency area peak power up to 4 kHz in click e-OAE significantly decreased in the middle and old age groups compared with those in the young age group. These results indicate the possibility that the function of cochlear micromechanics deteriorates in all cochlear partitions with increasing age, even in normal-hearing ears.

Pathophysiology of hearing impairment in acoustic neuroma with profound deafness: analysis by evoked otoacoustic emission and promontory stimulation test.

Evoked otoacoustic emissions (e-OAEs) were examined and promontory stimulus test (PST) done prior to tumor removal in 15 cases of surgically proven unilateral acoustic neuroma (AN) with more than 80 dB in pure-tone hearing level. The e-OAEs were elicited by tone-bursts at 1 kHz and 2 kHz, and an interaural difference in pseudothreshold of more than 10 dB was defined as a significant impairment of the cochlear function. In PST, electrical stimulation was applied by a burst mode at 6 stimulus frequencies between 50 Hz and 1600 Hz. The number of stimulus frequencies with a positive response was defined as the PST score. The results obtained were as follows; i) Mean interaural difference in e-OAE pseudothreshold was 16.0 dB at 1 kHz and 8.0 dB at 2 kHz, ii) Positive PST was found in only 40% of the subjects and the mean PST score was 0.93, iii). When the pathophysiology of hearing impairment was inferred from the combination of the findings in e-OAEs and PST, it was found that 33.3% of the subjects had pure cochlear impairment, 13.3% pure retrocochlear impairment and 46.7% cochlear-retrocochlear impairment. It is concluded that analysis of both e-OAEs and PST could clarify the pathophysiology of hearing impairment in AN with profound deafness, which cannot be determined by conventional psychoacoustic tests.