Reference data for ABRs in retrocochlear diagnosis

A retrospective analysis has been carried out on the auditory brainstem responses obtained in 235 female and 249 male neurologically normal patients. The analysis is focused on the wave latencies and the I-V and I-III intervals are compared with the classification parameters sex, age and high-frequency hearing loss. Since age and hearing loss are correlated, a multiple regression analysis is used to analyse the effects from the two variables. Both intervals are found to differ with sex (i.e. females display smaller values than males), to increase with age, and to decrease with hearing loss. Corrections are made for the classification parameters relative to 25 years and 0 dB HL. For the I-V interval, we find a mean value of 4.01 ms for the females and 4.19 ms for the males and a residual variance (SD) of 0.20 ms. For the I-III interval, we find a mean value of 2.13 ms for the females and 2.27 ms for the males and a residual variance (SD) of 0.16 ms. However, for the I-III interval, only the male data show dependence of hearing loss. In 78 patients, the electrocochleographic N1 is used to ensure the wave I latency and there is in general a good agreement between the two latency measures. However, in patients with profound high-frequency hearing loss differences up to 0.5 ms can be found.