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Fourth International Symposium and Workshops: Objective Measures in Cochlear Implants

Medical University of Hannover

01.06. bis 04.06.2005, Hannover

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Estimation of the refractory period based on electrically evoked compound action potentials

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  • corresponding author M. Sainz - Dpto. Cirugía y sus Especialidades, Universidad de Granada, 18071 Granada, Spain
  • A. de la Torre - Dpto. Electrónica y Tecn. Comp., Universidad de Granada, 18071 Granada, Spain
  • C. Roldán - Servicio ORL, Hospital Universitario S. Cecilio, 18012 Granada, Spain
  • I. Álvarez - Dpto. Electrónica y Tecn. Comp., Universidad de Granada, 18071 Granada, Spain
  • H. Spitzer - Institute of Applied Physics, University Innsbruck, Austria
  • H. Schößer - Med-El Medical Electronics, Worldwide Headquarters, Innsbruck, Austria
  • K. Veekmans - Med-El Medical Electronics, Worldwide Headquarters, Innsbruck, Austria
  • J.M. Ortigosa - Dpto. Electrónica y Tecn. Comp., Universidad de Granada, 18071 Granada, Spain

Medical University of Hannover, Department of Otolaryngology. Fourth International Symposium and Workshops: Objective Measures in Cochlear Implants. Hannover, 01.-04.06.2005. Düsseldorf, Köln: German Medical Science; 2005. Doc05omci088

The electronic version of this article is the complete one and can be found online at: http://www.egms.de/en/meetings/omci2005/05omci088.shtml

Published: May 31, 2005

© 2005 Sainz et al.
This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by-nc-nd/3.0/deed.en). You are free: to Share – to copy, distribute and transmit the work, provided the original author and source are credited.

Outline

Text

Introduction

The amplitude of compound action potentials is decreased when two consecutive stimuli separated by a short time interval are presented. This effect is consequence of the depolarization of the neurons with the first stimulus when the interval is shorter than the refractory period, because most neurons are not re-polarized and do not fire with the second stimulus. By controlling the interval between both stimuli, compound action potentials can be used to estimate the refractory period.

Materials and Methods

The study includes 4 patients implanted with the MED-EL Pulsar device. Evoked compound action potentials were recorded by means of the auditory response telemetry incorporated in this device. The responses were recorded by presenting groups of two stimuli separated by a controlled time-interval in the range 0.5ms–8ms. The function amplitude versus time-interval provides information about the refractory period of the neurons and about its distribution for the population of neurons.

Results

For time-intervals of 0.5ms no action potentials were observed. For 8ms, the responses were similar to that obtained with a single stimulus. The amplitude growth function (as a function of time-interval) presents differences among the patients. Patients with recent hearing experience presented the shortest refractory period (some response for 1.0ms), while patients with no hearing experience presented the longest one (no response until 6ms).

Conclusions

Compound action potentials provide an estimation of the refractory period of the neurons of the auditory nerve. Therefore, this objective measurement can be applied to evaluate the state of the neural ends in the vicinity of each electrode of the cochlear implant.