Exploiting Routine Clinical Measures to Inform Strategies for Better Hearing Performance in Cochlear Implant Users

Abstract

Neuroprostheses designed to interface with the nervous system to replace injured or missing senses can significantly improve a patient’s quality of life. The challenge remains to provide implants that operate optimally over several decades. Changes in the implant-tissue interface may precede performance problems. Tools to identify and characterize such changes using existing clinical measures would be highly valuable. Modern cochlear implant (CI) systems allow easy and regular measurements of electrode impedance (EI). This measure is routinely performed as a hardware integrity test, but it also allows a level of insight into the immune-mediated response to the implant, which is associated with performance outcomes. This study is a 5-year retrospective investigation of MED-EL CI users at the University of Southampton Auditory Implant Service including 176 adult ears (18–91) and 74 pediatric ears (1–17). The trend in EI in adults showed a decrease at apical electrodes. An increase was seen at the basal electrodes which are closest to the surgery site. The trend in the pediatric cohort was increasing EI over time for nearly all electrode positions, although this group showed greater variability and had a smaller sample size. We applied an outlier-labeling rule to statistically identify individuals that exhibit raised impedance. This highlighted 14 adult ears (8%) and 3 pediatric ears (5%) with impedance levels that deviated from the group distribution. The slow development of EI suggests intra-cochlear fibrosis and/or osteogenesis as the underlying mechanism. The usual clinical intervention for extreme impedance readings is to deactivate the relevant electrode. Our findings highlight some interesting clinical contradictions: some cases with raised (but not extreme) impedance had not prompted an electrode deactivation; and many cases of electrode deactivation had been informed by subjective patient reports. This emphasizes the need for improved objective evidence to inform electrode deactivations in borderline cases, for which our outlier-labeling approach is a promising candidate. A data extraction and analysis protocol that allows ongoing and automated statistical analysis of routinely collected data could benefit both the CI and wider neuroprosthetics communities. Our approach provides new tools to inform practice and to improve the function and longevity of neuroprosthetic devices.

Intraoperative Impedance-Based Estimation of Cochlear Implant Electrode Array Insertion Depth

“…The resulting distribution of basal interface impedances computed from the apical distribution according to (17) is overlaid in Fig. 6 (bottom right, green) and shows acceptable agreement with the measured distribution.…”

“…The implants perform telemetry measurements with charge balanced, rectangular biphasic cathodic-first pulses with an amplitude of I stim ≈ 300 µA and a pulse-width of 24 µs [16]. The voltage potential on the recording electrode is measured at the end of the anodic phase [17] with respect to a large ground electrode located on the implant body. A schematic drawing of the current stimulus and resulting voltage on the electrode is shown in Fig.…”

Cochlear implant failure following COVID 19: Report of two cases

“…CI failures may be due to device (hard) failure, soft failure, or surgical complications. Soft failure is a condition in which the implant device passes the integrity test but patients experience declining speech comprehension or non-auditory aversive symptoms [ 6 , 10 ]. In the present study, the “short circuits” condition was observed in half of the electrodes in both cases.…”

“…The CI device presents a sequence of current pulses, similar to those produced by the biological hearing system, via a platinum multi-electrode array located in the cochlea. It has been demonstrated that CI recipients typically experience improved speech comprehension and speech production ability [ 6 ].…”

Noise Induced Hearing Loss and Tinnitus—New Research Developments and Remaining Gaps in Disease Assessment, Treatment, and Prevention

“…Poor outcomes cannot always be explained, although successful outcomes are predominant. Today, cochlear implant hearing performance can be measured in situ, which is a relatively new research method and expected to improve the success rate of cochlear implants [ 54 , 55 ].…”