Fine-grain recordings of the electrically evoked compound action potential amplitude growth function in cochlear implant recipients

Abstract

BackgroundIn cochlear implants (CI) measuring the electrically evoked compound action potential (ECAP) has become an important tool for verifying the electrode-nerve interface as well as establishing a basis for a map to program the speech processor. In a standard clinical setup recordings are averaged over 25–100 repetitions to allow for the detection of ECAPs within the noise floor. To obtain an amplitude growth function, these measurements are normally performed for 5–10 different stimulation levels. We evaluate a recording paradigm where the stimulation intensity is increased in quasi-continuous steps and instead of averaging repeated recordings with identical stimulation parameters, running averages over small intervals of stimulation levels are computed. The first visible nerve response was manually identified by two experts.ResultsBoth recording paradigms were evaluated in 39 cochlear implants, showing an on average lower threshold of the first nerve response for the quasi-continuous measurement paradigm (Wilcoxon signed-rank test, p = 6.2e−08) compared to the clinical standard paradigm. The mean maximal loudness over all implants and stimulation electrodes was 13% lower at the 80 pulses/s quasi-continuous paradigm compared to the 44 pulses/s clinical standard paradigm.ConclusionsBeside a more robust determination of the ECAP threshold, the proposed quasi-continuous stimulation paradigm results in a more robust behavioral feedback of the CI user upon the maximal acceptable loudness percept. Furthermore this paradigm can also reveal the fine-structure in the amplitude growth function.

Amplitude Growth Functions of Auditory Nerve Responses to Electric Pulse Stimulation With Varied Interphase Gaps in Cochlear Implant Users With Ipsilateral Residual Hearing

“…The amplitude of the single pulse electric stimulation in charge units (nC) was steadily increased in a continuous paradigm ( Gärtner et al., 2018 ). Upon reaching the loudest acceptable presentation level, which the subject indicated in real time, the stimulation of the current electrode was stopped.…”

Optimized SNR-based ECAP threshold determination is comparable to the judgement of human evaluators

“…Measurements were recorded via the MAX Programming Interface (MED-EL Medical Electronics, Innsbruck, Austria) connected to a personal computer running the research software that is described in [ 7 ]. Symmetric charge-balanced biphasic pulses were used to elicit the nerve response.…”

“…This limits the resolution at which the ECAP threshold can be determined. This problem was addressed in the design of the FineGrain stimulation paradigm [ 7 ], which samples the AGF in smaller stimulus steps and thus provides the means to use the higher ECAP AGF resolution for more accurate ECAP threshold determination. As a further development of this idea, FineGrain was combined with an automatic threshold determination approach, available as AutoART in the MAESTRO software (MED-EL Medical Electronics, Innsbruck, Austria) since 2017, version 7 and higher [ 7 , 8 ].…”

“…However, it is likely that the precision of the approach would equally benefit from a higher resolution of the ECAP responses, as previously seen in AGF-based approaches. The novel FineGrain-SNR (FG-SNR) formalism is an extension of the SNR approach [ 11 ], which allows for single ECAP responses like those used with the FineGrain stimulation paradigm [ 7 ]. Here, we show that ECAP thresholds calculated with the FG-SNR algorithm are comparable with the thresholds determined by experienced clinicians.…”

Measurements of the local evoked potential from the cochlear nucleus in patients with an auditory brainstem implant and its implication to auditory perception and audio processor programming

“…Results from measurements taken by the AutoART task, benefitting from the fine-grain recording of the response [ 13 ], were additionally used in subject A-01. Only in this case, a different stimulation rate of 60 pps was used.…”