Effect of Increasing Pulse Phase Duration on Neural Responsiveness of the Electrically Stimulated Cochlear Nerve

Effect of Increasing Pulse Phase Duration on Neural Responsiveness of the Electrically Stimulated Cochlear Nerve: Objectives:

The aim of this study is to (1) investigate the effects of increasing the pulse phase duration (PPD) on the neural response of the electrically stimulated cochlear nerve (CN) in children with CN deficiency (CND) and (2) compare the results from the CND population to those measured in children with normal-sized CNs.

Design:

Study participants included 30 children with CND and 30 children with normal-sized CNs. All participants used a Cochlear Nucleus device in the test ear. For each subject, electrically evoked compound action potential (eCAP) input/output (I/O) functions evoked by single biphasic pulses with different PPDs were recorded at three electrode locations across the electrode array. PPD durations tested in this study included 50, 62, 75, and 88 μsec/phase. For each electrode tested for each study participant, the amount of electrical charge corresponding to the maximum comfortable level measured for the 88 μsec PPD was used as the upper limit of stimulation. The eCAP amplitude measured at the highest electrical charge level, the eCAP threshold (i.e., the lowest level that evoked an eCAP), and the slope of the eCAP I/O function were measured. Generalized linear mixed effect models with study group, electrode location, and PPD as the fixed effects and subject as the random effect were used to compare these dependent variables measured at different electrode locations and PPDs between children with CND and children with normal-sized CNs.

Results:

Children with CND had smaller eCAP amplitudes, higher eCAP thresholds, and smaller slopes of the eCAP I/O function than children with normal-sized CNs. Children with CND who had fewer electrodes with a measurable eCAP showed smaller eCAP amplitudes and flatter eCAP I/O functions than children with CND who had more electrodes with eCAPs. Increasing the PPD did not show a statistically significant effect on any of these three eCAP parameters in the two subject groups tested in this study.

Conclusions:

For the same amount of electrical charge, increasing the PPD from 50 to 88 μsec for a biphasic pulse with a 7 μsec interphase gap did not significantly affect CN responsiveness to electrical stimulation in human cochlear implant users. Further studies with different electrical pulse configurations are warranted to determine whether evaluating the eCAP sensitivity to changes in the PPD can be used as a testing paradigm to estimate neural survival of the CN for individual cochlear implant users.

ACKNOWLEDGMENTS: The authors gratefully thank all subjects and their parents for participating in this study.

S.H. designed the study, participated in data collection and patient testing, and drafted and approved the final version of this manuscript. J.S. participated in data analysis, provided critical comments, and approved the final version of this manuscript. L.X., X.C., W.J.R., R.W., C.V., J.L., M.S., and C.W. participated in data collection and patient testing, provided critical comments, and approved the final version of this manuscript.

This work was supported by the R01 grant from National Institute on Deafness and Other Communication Disorders (R01DC017846) and NIDCD and National Institute of General Medical Sciences (R01DC016038).

Portions of this project were presented at the 2019 Conference on Implantable Auditory Prostheses, July 14-19, Lake Tahoe, CA.

The authors have no conflicts of interest to declare.

Received September 18, 2019; accepted February 13, 2020.

Address for correspondence: Shuman He, Department of Otolaryngology – Head and Neck Surgery, Eye and Ear Institute, The Ohio State University, 915 Olentangy River Road, Suite 4000, Columbus, OH 43212, USA. E-mail: shuman.he@osumc.edu

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