Hansjoerg Schoesser1, Peter Nopp1, Ilona Anderson1, Martina Deibl1, Philipp Spitzer1, Alexander Moeltner1, Wilma Harnisch2, Stefan Brill2, Joachim Mueller2

1MED-EL Medical Electronics GmbH, Innsbruck, Austria/2University ENT-Clinic Würzburg, Würzburg, Germany

■ INTRODUCTION: The use of objective measures, especially the recording of the Electrically Evoked Compound Action Potential (ECAP) as a direct response of the auditory nerve to electrical stimulation, is widely spread in the field of cochlear implantation. This measurement is particularly advantageous because it allows the clinician to directly measure auditory nerve fibres potentials while observing the evoked electrical activity of the auditory nerve. In an earlier study, Zimmerling & Hochmair (2002) found that for a given recording electrode, amplitude growth functions show characteristic differences in shape and absolute amplitude, when stimulation site is varied, suggesting that a different neural population contributes to the response. An interesting observation was that ECAP amplitudes tend to be slightly larger at the apical contacts. However, the subjects in that study were Ineraid patients with a different type of electrode, which does not reach the apical region in the second turn of the cochlea. Therefore, it would be particularly interesting to see if this trend also continues, when stimulating more apical with the MED-EL standard electrode.

■ METHOD: Together with the standard electrode of the PULSARci100 which offers the possibility of a complete cochlear coverage the Auditory Nerve Response Telemetry (ART) offers the possibility of full panorama ECAP recordings. Subjects were recruited from 13 centres in order to evaluate post-operative ECAP recordings with the PULSARci100 in combination with the MAESTRO system software. The subdivision of the electrode into an apical, middle and basal region allows a statistical comparison of the neural responses of these cochlear regions.

■ DISCUSSION: The clinical results of this study show a dependency of the ECAP responses on the stimulation site within the cochlea. Especially the apical regions show higher response amplitudes and a steeper slope of the amplitude growth functionthan the middle and the basal regions in many subjects. The reason for that could be a higher survival rate and thus a higher number of nerve fibres or a shorter distance between the electrodes and the neural structures respectively.