Electrically evoked compound action potentials are different depending on the site of cochlear stimulation

Abstract

One of the many parameters that can affect cochlear implant (CI) users' performance is the site of presentation of electrical stimulation, from the CI, to the auditory nerve. Evoked compound action potential (ECAP) measurements are commonly used to verify nerve function by stimulating one electrode contact in the cochlea and recording the resulting action potentials on the other contacts of the electrode array.The present study aimed to determine if the ECAP amplitude differs between the apical, middle, and basal region of the cochlea, if double peak potentials were more likely in the apex than the basal region of the cochlea, and if there were differences in the ECAP threshold and recovery function across the cochlea.ECAP measurements were performed in the apical, middle, and basal region of the cochlea at fixed sites of stimulation with varying recording electrodes. One hundred and forty one adult subjects with severe to profound sensorineural hearing loss fitted with a Standard or FLEX SOFT electrode were included in this study. ECAP responses were captured using MAESTRO System Software (MED-EL). The ECAP amplitude, threshold, and slope were determined using amplitude growth sequences. The 50% recovery rate was assessed using independent single sequences that have two stimulation pulses (a masker and a probe pulse) separated by a variable inter-pulse interval. For all recordings, ECAP peaks were annotated semi-automatically.ECAP amplitudes were greater upon stimulation of the apical region compared to the basal region of the cochlea. ECAP slopes were steeper in the apical region compared to the basal region of the cochlea and 251 ECAP thresholds were lower in the middle region compared to the basal region of the cochlea. The incidence of double peaks was greater upon stimulation of the apical region compared to the basal region of the cochlea. This data indicates that the site and intensity of cochlear stimulation affect ECAP properties.

Effect of Cochlear Implant Electrode Array Design on Electrophysiological and Psychophysical Measures: Lateral Wall versus Perimodiolar Types

“…The ECAP threshold was lower for PM than for LW whereas it was lower on the apical region than on the basal and medial regions. It is consistent with some previous findings [17-19]. Telmesani and Said [17] showed that the ECAP threshold was lower for PM than for LW at the basal site of electrode in the pediatric CI users when the ECAP response was measured on the apical (electrode 22), mid (electrode 16 and 11), and basal regions (electrode 6 and 1).…”

The Electrically Evoked Compound Action Potential: From Laboratory to Clinic

“…In addition to the single-peak response, eCAPs with two positive peaks (P1 and P2) have been observed (Stypulkowski and van den Honert, 1984 ; Lai and Dillier, 2000 ; van de Heyning et al, 2016 ). This type of response has been referred to as a double-peak or a Type II nerve response (Lai and Dillier, 2000 ).…”

“…This type of response has been referred to as a double-peak or a Type II nerve response (Lai and Dillier, 2000 ). For this type of eCAP response, the P1 typically occurs around 0.4–0.5 ms and the P2 typically occurs around 0.6–0.7 ms (Lai and Dillier, 2000 ; van de Heyning et al, 2016 ). The incidence of the Type II response is around 10–20% (Lai and Dillier, 2000 ; van de Heyning et al, 2016 ).…”

“…For this type of eCAP response, the P1 typically occurs around 0.4–0.5 ms and the P2 typically occurs around 0.6–0.7 ms (Lai and Dillier, 2000 ; van de Heyning et al, 2016 ). The incidence of the Type II response is around 10–20% (Lai and Dillier, 2000 ; van de Heyning et al, 2016 ). The lower panel of Figure 1 shows an example of a Type II response measured in a prelingually deaf child with a Cochlear N5 CI.…”

“…The speed of the increase can be quantified by the slope of an eCAP input-output (I/O) function. In addition, eCAPs recoded at the apical electrodes tend to have larger amplitudes than those recorded at the basal electrodes at an equal stimulus or loudness level (e.g., Frijns et al, 2002 ; Polak et al, 2004 ; Brill et al, 2009 ; van de Heyning et al, 2016 ; Tejani et al, 2017 ). Potential factors accounting for the increase in eCAP amplitude toward the apical region include better neural survival and shorter distance between the test electrode and the stimulated neural structure at the apex.…”