Tympanic ECochG and conventional ABR: a combined approach for the identification of wave I and the I-V interwave interval.

Identification of wave I and measurement of the I-V interwave interval (IWI) are important parameters of the auditory brain stem response (ABR). However, at low stimulus sensation levels, wave I may be absent in the presence of wave V when the ABR is recorded conventionally with scalp electrodes. Several studies have shown that the amplitude and detectability of wave I (or N1) can be enhanced via extratympanic electrocochleography (ECochG), and even more so with tympanic ECochG. In the present study, tympanic ECochG was combined with conventional ABR to compare the amplitude and sensitivity of N1, wave I, and wave V in normally hearing subjects, and to identify the N1-V IWI in hearing impaired subjects whose conventional ABRs did not contain a reliable wave I. For the normally hearing subjects, the amplitude of the N1 was considerably larger than the amplitudes of waves I and V of the conventional ABR and there was no significant difference between N1 and wave V thresholds. For the hearing impaired group, the combined ECochG-ABR approach allowed for the identification of N1 and measurement of the N1-V IWI in all subjects. Our results support the use of tympanic ECochG in combination with conventional ABR for certain audiological and neurological applications.