• Taryn Davids, Jerome Valero, Blake C Papsin, Robert V Harrison, and Karen A Gordon.
• Division of Otolaryngology-Head and Neck Surgery,University of Toronto, Toronto, Ontario. taryndavids@hotmail.com
• J Otolaryngol Head N. 2008 Aug 1; 37 (4): 559-64.

ObjectiveElectrophysiologic responses used to predict behavioural stimulation levels in implant users are typically evoked with a single-pulse stimulus versus higher-rate pulse trains of longer duration. Unfortunately, electrophysiologic measures tend to overestimate behavioural responses. It may be possible to improve the predictive ability of evoked potential thresholds by increasing the duration of the stimulus. We asked if auditory brainstem and middle latency responses can be reliably measured using electrical pulse trains of increasing duration.DesignEvoked potential testing was performed in five pediatric N24RE cochlear implant users aged 7.6 to 14.9 years.SettingCochlear Implant Program, Cochlear Implant Laboratory, The Hospital for Sick Children, Toronto.MethodsResponses were electrically evoked for durations of 2, 6, and 10 milliseconds by single pulses and pulse trains of 500 pulses per second.Main Outcome MeasuresEvoked auditory brainstem response (EABR) and evoked middle latency response (EMLR) waveform latencies and amplitudes were compared between durations.ResultsClear and replicable EABRs and EMLRs were recorded for all durations. There was no significant change in EABR wave eV latency relative to the stimulus offset. There was no significant change in EMLR wave latencies relative to the stimulus onset. This was confirmed by a linear decrease in the interwave latency between the EABR wave eV and the EMLR wave eNa. No significant changes in wave amplitude were found as the pulse train duration increased for the EABR or the EMLR.ConclusionsEABRs are dominated by the stimulus offset, whereas EMLRs appear to be dominated by stimulus onset. Clear, unchanging EABRs and EMLRs indicated that electrophysiologic measures were a valid tool for increasing durations.

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