Electrical compound action potentials recorded with automated neural response telemetry: threshold changes as a...

Area of Science:

• Audiology
• Biomedical Engineering
• Neuroscience

Background:

• Neural Response Telemetry (NRT) using electrically evoked compound action potential (ECAP) thresholds aims to objectively predict psychophysical measurements for cochlear implant (CI) programming.
• Accurate ECAP threshold prediction is crucial for programming speech processors, especially in young children or individuals unable to provide reliable behavioral data.
• Previous ECAP studies were limited to the CI24 device; the Nucleus Freedom device introduced an enhanced AutoNRT program for lower-level ECAP threshold measurements.

Purpose of the Study:

• To investigate the hypothesis that the enhanced AutoNRT program improves the predictability of postoperative measurements from intraoperative ECAP thresholds.
• To track ECAP thresholds obtained using AutoNRT as a function of time and electrode position in Nucleus Freedom CI users.

Main Methods:

• ECAP thresholds were recorded from 71 children and adults with Nucleus Freedom cochlear implants using the AutoNRT protocol.
• Measurements were taken at surgery, initial stimulation, and 3 months post-stimulation.
• Five electrodes (basal, middle, apical positions) were tested at each interval, and thresholds were compared.

Main Results:

• Significant variations in AutoNRT ECAP thresholds were observed based on time and electrode position.
• Basal electrodes consistently showed higher ECAP thresholds than apical electrodes.
• ECAP thresholds decreased from surgery to initial stimulation, stabilizing by 3 months post-stimulation; children exhibited lower thresholds than adults.

Conclusions:

• Significant temporal changes in AutoNRT ECAP thresholds limit their direct use for predicting postoperative measurements.
• Mid-array electrodes (11 and 16) demonstrated the least threshold variation over time, making them suitable for estimating postoperative ECAP thresholds.
• Intraoperative mid-array ECAP thresholds may assist in initial cochlear implant programming when behavioral or other electrophysiological data are absent.