Visualizing Contralateral Suppression of Hearing Sensitivity via Acoustic and Electric Brainstem Audiometry in Bimodal Cochlear Implant Patients: A Feasibility Study

Abstract

<b><i>Introduction:</i></b> The medial olivocochlear reflex (MOCR) is a part of the binaural processing strategies and influences the efferent auditory pathway in normal-hearing individuals. Patients with asymmetric hearing loss often benefit from a bimodal hearing solution with a cochlear implant (CI) and a hearing aid (HA). However, hearing performances may vary with some surprisingly high- or low-performing CI/HA users. A potential role of the MOCR among these patients warrants further investigation. Otoacustics emissions are an established method to visualize the reflex; however, this technique implies some disadvantages. To visualize the MOCR via auditory brainstem response (ABR) could be a promising alternative. <b><i>Methods:</i></b> Twenty-three bimodal CI/HA users were enrolled. Experimental setup was as follows: I. electrical ABR on the CI side was recorded with and without simultaneous contralateral noise signal at the HA side, II. acoustic ABR was recorded on the HA side with and without simultaneous contralateral noise at the CI side. Brainstem thresholds and amplitudes of waveforms I–V with and without contralateral noise were compared. Potential correlations of patient-related factors and hearing performances were analysed. <b><i>Results:</i></b> In four individuals, a reduction of brainstem audiometry thresholds could be observed at the acoustic brainstem audiometry. In these cases, results could be reproduced. Summarizing ABR measurements at the HA side of all individuals, no relevant changes of ABR thresholds (dB nHL) or waveform amplitude reductions (nV) could be observed irrespective of the presence or absence of a contralateral suppression signal. <b><i>Conclusion:</i></b> Threshold changes of acoustic ABR upon presentation of a contralateral suppression signal could not generally be measured in bimodal CI users. However, in a subgroup, a highly reproducible effect was demonstrated if a contralateral suppression signal was applied. A reactivated rather than rehabilitated MOCR may have accounted for this effect in this subgroup. One could speculate that in these patients, bimodal fitting could be affected by the MOCR efferents.

The Effects of Stimulus Repetition Rate on Electrically Evoked Auditory Brainstem Potentials in Postlingually Deafened Adult Cochlear Implant Recipients

“…An additional application of the prediction model [3] could be the interpretation of electrophysiological measurements based on prior classification of groups of recipients in respect of the WRS GAP . Other recent work [8,[12][13][14][15] led to the proposal and use of a setting for electrically evoked auditory brainstem responses (EABR) mimicking the established acoustic broadband click. Reference values for latencies were assessed by including only CI recipients with word recognition score with cochlear implant at 65 dB (WRS 65 (CI)) of 50% or more [13].…”