Measures of the electrically evoked compound action potential threshold and slope in HiRes 90K^TMusers

Abstract

The observed effects of electrode position are consistent with a model in which eCAP threshold is governed primarily by an effect of distance between electrode and neural interface (which is shorter towards the apex of the cochlea) and in which slope is governed primarily by density of surviving neural elements.

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

“…In 89% of the electrodes, the ECAP AGF could be reliably measured. Similarly, Nehme and colleagues (Nehme et al, 2014) measured ECAP AGFs in 34 children and adults using the Advanced Bionics HiRes90K™ device and reported that these measures could be reliability obtained on 91% of the electrodes tested. Data were initially analyzed using several methods to include sigmoidal functions and an area under the curve analysis.…”

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

“…In animal models, several studies demonstrated that the slope of the ECAP AGF is a predictor of the number of remaining nerve fibers or 'neural status' of the ear (Hall, 1990;Pfingst et al, 2015Pfingst et al, , 2017Ramekers et al, 2014). Earlier, it has been proposed that the slope in humans is proportional to the neural density (Cullington, 2003) while the ECAP threshold is affected by the distance between the stimulating electrode and the excitable part of the neurons (Nehmé et al, 2014). A simplified graphical representation of this idea (Fig.…”

“…2) illustrates that despite similar distance of electrode to neurons, a lower neural density (a versus b) would result in the same ECAP thresholds but different slopes. The basis for this lies within a model wherein the ECAP amplitude represents the number of responding neurons (Cullington, 2003;Kim et al, 2010;Nehmé et al, 2014). A detailed computer model indicated that the ECAP amplitude does indeed increase with the number of responding neurons but only until certain stimulation amplitudesat very high stimulation intensities, ECAP amplitudes start decreasing again (Briaire and Frijns, 2005).…”

“…To date there is no proof of slope being a predictor of neural status in humans, however there are indications from research that point towards a similar direction: For instance, consistent with the animal data on flatter slopes correlating with poor neuronal survival, He et al (2018) observed a significantly shallower slope in children with cochlear nerve deficiency compared to children with normal sized cochlear nerve. Nehmé et al (2014) compared slopes from Advanced Bionics HiRes90K device-users with congenital and acquired hearing loss and found a steeper median slope (and a broader variation) for the former. Congenital hearing loss can present as a wide variety of structural deficiencies, while acquired hearing loss, on the other hand, often involves degradation processes of hair cells and, in consequence, neurons (Liberman and Kujawa, 2017).…”

Responsiveness of the Electrically Stimulated Cochlear Nerve in Children With Cochlear Nerve Deficiency

“…The primary variable of interest for the eCAP I/O function is the slope because it is positively associated with the density of the surviving neural population, with steeper slopes indicating greater density (e.g. Kim et al, 2010; Nehmé et al, 2014). In addition to the slope, two other parameters are commonly assessed: the lowest stimulation level that can evoke an eCAP (i.e.…”