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Cochlear Implants International
An Interdisciplinary Journal for Implantable Hearing Devices
Volume 22, 2021 - Issue 3
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Original articles

Slope of electrically evoked compound action potential amplitude growth function is site-dependent

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Abstract

Objectives

In human cochlear implant (CI) recipients, the slope of the electrically evoked compound action potential (ECAP) amplitude growth function (AGF) is not very well investigated, in comparison to the threshold derived from the AGF. This is despite the fact that it was shown in animal experiments that the slope correlates with the number of excitable neurons. The rationale of this study was to establish baseline data of the AGF slope for possible clinical applications, while investigating stability over time and dependence on cochlear site.

Design

ECAP AGFs of 16 ears implanted with MED-EL CIs were recorded on all electrode contacts during the normal clinical routine at 4 different points in time.

Results

Due to patient availability, not all 16 ears could be measured at all 4 points in time. A dependence of the slope on the electrode position was visible and statistically significant: At the three electrode contacts at the apical end of the array, the slope is greater compared to the medial and basal region of the cochlea.

Conclusion

The three most apical electrode contacts show greater slopes of ECAP AGF recordings. Our data of the cohort slopes show mild effects between the 4 different points in time.

Acknowledgments

The authors would like to thank the participants of the study who agreed that their data could be used for analysis. We also would like to thank Marko Takanen for helpful discussions on statistical modelling, Philipp Spitzer for helpful discussions regarding the simplified neural model and both Kathrin Lauss and Philipp Spitzer for help with wording and proof-reading the manuscript. We thank the reviewers for helpful comments and suggestions based on those we were able to improve the analysis.