[Dip-shaped hearing loss of Békésy audiogram in high school students]

Small dip-shaped hearing loss may be frequently observed on Bekesy audiograms in ears without any hearing loss on pure tone audiograms. Hearing tests and otoacoustic emission measurements were performed in club member of 2 senior high schools (K-D School and S-D School), in order to determine any relationship between inner ear impairments and the small dips on Bekesy audiograms. In the kendo, soccer, tennis and orchestral music clubs of K-D School micro-dips in depth over 10 dB were found to have incidences between 40% and 53%, and the micro-dips were distributed in frequencies above 5 kHz. In the of kendo, tennis, brass band and tea ceremony clubs of S-D School the incidences of micro-dips ears were between 30% and 48%, and the micro-dips tended to be distributed in higher frequencies except in the tea ceremony club. The micro-dips in the ears of the tea ceremony club members were distributed over all the frequencies examined, but most of them disappeared when counted for dip size above 15 dB remaining an ear at 7.5 kHz. Incidences of earphone or headphone users as a hobby were in the range of 30 to 70% in members of all clubs. There were no characteristic findings of clubs in the incidences of the earphone or headphone users. The degree of association between the micro-dip ears and the use of earphone or headphone was low. C-EOAEs which had a 6 ms or longer duration of evoked otoacoustic emissions were detected with an incidence of 40 to 65% and there was a significant association between the micro-dip ears and the C-EOAE ears. Incidences of spontaneous otoacoustic emissions were between 26% and 28% in all clubs and there were differences in the incidences between sexes. The frequency distribution of the spontaneous otoacoustic emissions were remarkably different to that of the micro-dips. To determine whether the C-EOAEs express a predisposition to inner ear susceptibility to noise-induced hearing loss and to ascertain that the micro-dip is a precursor notice to noise-induced hearing loss, further follow-up surveys are needed.