Self-assessment of cochlear health by cochlear implant recipients

Abstract

Recent technological advances in cochlear implant (CI) telemetry have enabled, for the first time, CI users to perform cochlear health (CH) measurements through self-assessment for prolonged periods of time. This is important to better understand the influence of CH on CI outcomes, and to assess the safety and efficacy of future novel treatments for deafness that will be administered as adjunctive therapies to cochlear implantation. We evaluated the feasibility of using a CI to assess CH and examined patterns of electrode impedances, electrically-evoked compound action potentials (eCAPs) and electrocochleography (ECochGs), over time, in a group of adult CI recipients. Fifteen subjects were trained to use the Active Insertion Monitoring tablet by Advanced Bionics, at home for 12 weeks to independently record impedances twice daily, eCAPs once weekly and ECochGs daily in the first week, and weekly thereafter. Participants also completed behavioral hearing and speech assessments. Group level measurement compliance was 98.9% for impedances, 100% for eCAPs and 99.6% for ECochGs. Electrode impedances remained stable over time, with only minimal variation observed. Morning impedances were significantly higher than evening measurements, and impedances increased toward the base of the cochlea. eCAP thresholds were also highly repeatable, with all subjects showing 100% measurement consistency at, at least one electrode. Just over half of all subjects showed consistently absent thresholds at one or more electrodes, potentially suggesting the existence of cochlear dead regions. All subjects met UK NICE guidelines for cochlear implantation, so were expected to have little residual hearing. ECochG thresholds were, unsurprisingly, highly erratic and did not correlate with audiometric thresholds, though lower ECochG thresholds showed more repeatability over time than higher thresholds. We conclude that it is feasible for CI users to independently record CH measurements using their CI, and electrode impedances and eCAPs are promising measurements for objectively assessing CH.

Keywords: cochlear implant; electrically-evoked compound action potential; electrocochleography; electrode impedance; hearing loss; neural response telemetry.

Figure 1

AIM system components. (1) AIM tablet; (2) CI sound processor; (3) CI headpiece magnet and cable; (4) programming cable; (5) AIM insert earphone connector; and (6) acoustic tube with yellow foam ear tip.

Figure 2

Scatter graphs displaying individual electrode impedances at all 16 electrodes over 12 weeks (N = 15). Two points (both AM and PM) are plotted for each day.

Figure 3

Individual and group level electrode impedance standard deviations plotted across the electrode array. Colored lines represent each individual participant (N = 15), and the black dotted line shows group average standard deviations.

Figure 4

Boxplots displaying group level mean AM and PM impedances. Mean values calculated from the four electrode groupings are shown (N = 15).

Figure 5

Bar charts displaying each subject's eCAP threshold from all four recording electrodes over the 12-week testing period (N = 15).

Figure 6

Boxplots displaying group level eCAP data at each of the four recording electrodes. All successful thresholds from the entire cohort (N = 15) are included. Specifically, 159, 116, 117, and 122 thresholds (out of a maximum of 180) are included from e1, e5, e9, and e13, respectively. Median values fell within the range of 150–200 cu across all four electrodes.

Figure 7

Boxplots displaying group level ECochG thresholds across the frequency range. Data from all 15 subjects are compiled, resulting in considerable differences in numbers of valid thresholds at each frequency.