[Practical study of evoked otoacoustic emissions concerning individual variation of noise susceptibility]

There are large individual differences in susceptibility to noise exposure. Most hearing impairment begins with dip type hearing loss, and continual evoked otoacoustic emissions (C-EOAEs) are frequently seen in ears with dip type hearing loss. The present study was performed in order to ascertain the relationship between dip type hearing loss and C-EOAE. Brass band members in two junior high schools were the subjects of this study. In H-school, the noise levels during practice were between 88 and 103 dB Leq in all groups with music instrumental parts. The survey revealed that 58% of ears showed dip type hearing loss in Békésy's audiogram and 52% showed of C-EOAE. The incidence of dip was 82% in ears with C-EOAE, and 35% in the ears without C-EOAE. In the brass band members of F-school the incidence of ears having dip was 64% and the incidence of C-EOAE was 56%. The incidence of dip was 81% in the ears with C-EOAE, whereas it was 43% in the ears without C-EOAE. Follow-up studies in the subjects of H-school revealed that the incidence of dip ears decreased from 58% to 45%, whereas the incidence of C-EOAE changed in only one ear and was maintained at 50%, near the initial value. Four ears changed in of dip without any change in the presence of C-EOAE. This practical survey showed a clear relationship between the presence of dip and of C-EOAE.(ABSTRACT TRUNCATED AT 250 WORDS)