Across-site patterns of electrically evoked compound action potential amplitude-growth functions in multichannel cochlear implant recipients and the effects of the interphase gap

Abstract

Electrically evoked compound action potential (ECAP) measures of peak amplitude, and amplitude-growth function (AGF) slope have been shown to reflect characteristics of cochlear health (primarily spiral ganglion density) in anesthetized cochlear-implanted guinea pigs. Likewise, the effect of increasing the interphase gap (IPG) in each of these measures also reflects SGN density in the implanted guinea pig. Based on these findings, we hypothesize that suprathreshold ECAP measures, and also how they change as the IPG is increased, have the potential to be clinically applicable in human subjects. However, further work is first needed in order to determine the characteristics of these measures in humans who use cochlear implants. The current study examined across-site patterns of suprathreshold ECAP measures in 10 bilaterally-implanted, adult cochlear implant users. Results showed that both peak amplitude and slope of the AGF varied significantly from electrode to electrode in ear-specific patterns across the subjects’ electrode arrays. The pattern of across-site performance within each measure (e.g., peak amplitude or slope) varied across subjects and ears. As expected, increasing the IPG on average increased the peak amplitude and slope. Across ears, there was a significant, negative correlation between the slope of the ECAP AGF and the duration of hearing loss. Across-site patterns of ECAP peak amplitude and AGF slopes were also compared with common ground impedance values and significant correlations were observed in some cases, depending on the subject and condition. The results of this study, coupled with previous studies in animals, suggest that it is feasible to measure the change in suprathreshold ECAP measures as the IPG increases on most electrodes. Further work is needed to investigate the relationship between these measures and cochlear implant outcomes, and determine how these measures might be used when programming a cochlear-implant processor.

The Electrically Evoked Compound Action Potential: From Laboratory to Clinic

“…Therefore, animal models are used to identify eCAP measures that are sensitive to neural survivals (e.g., Miller et al, 1994 ; Prado-Guitierrez et al, 2006 ; Ramekers et al, 2014 ). These measures have been subsequently used in human CI users to evaluate their correlations with behavioral measures of auditory perception and/or speech perception (e.g., Brown et al, 1990 ; Gantz et al, 1994 ; Kim et al, 2010 ; Pfingst et al, 2015a ; Schvartz-Leyzac and Pfingst, 2016 ). This section reviews studies related to one eCAP measure that has been studied for many years (i.e., slope of the eCAP I/O function) and the three most recently developed eCAP measures (sensitivity to inter-phase-gap, phase duration and pulse polarity).…”

“…However, the spiral ganglion density only accounted for 50% of the variance in the slope of eCAP I/O function (Pfingst et al, 2014 ). In human CI users, flatter slopes have been found to be associated with longer duration of hearing loss (e.g., Schvartz-Leyzac and Pfingst, 2016 ). Studies evaluating the association between the slope of eCAP I/O function and speech perception scores in human CI users show inconsistent results.…”

“…To date, the effect of increasing IPG on eCAP responses in human CI users has been only examined in one study. Schvartz-Leyzac and Pfingst ( 2016 ) studied the effect of increasing IPG from 7 to 30 μs on eCAP amplitude and slope of I/O function in human CI users. Their results showed that increasing IPG generally yielded increased eCAP amplitude and steeper slopes of I/O function.…”

Lautheitsoptimierte Messung von Summenaktionspotentialen bei Cochlea Implantat Trägern

“…Abweichend von den Standardeinstellungen der Software wurde die Pulsbreite von 25 µs auf bis zu 100 µs erhöht sowie die Pause zwischen den beiden biphasischen Pulsen (IPG, Interphasegap) von 7 µs auf 25 µs erhöht. Grund hierfür waren eigene praktische Erfahrungen und tierexperimentelle Befunde [22,23]…”

Suprathreshold compound action potential amplitude as a measure of auditory function in cochlear implant users

“…Although a broad (monopolar) stimulation mode and the use of relatively high current levels results in a broad spread of current and potential recruitment of neurons from across the cochlea, the neurons closest to the recording electrodes likely influence the amplitude more than neurons farther away (discussed in Miller et al., 2008 ). Amplitude of the recorded eCAP varies as the stimulation and recording sites are varied across intracochlear electrodes in CI users, even when the stimulation mode is broad ( DeVries et al., 2016 , Schvartz-Leyzac and Pfingst, 2016 ). Moreover, the amplitude profile varies in a manner that is unique to the individual.…”