Cochlear Implant Electrode Research Articles

A Novel Algorithm to Analyze Multi-Frequency Electrocochleography Measurements to Monitor Electrode Placement During Cochlear Implant Surgery

Objectives: During cochlear implant (CI) electrode placement, single low-frequency (e.g., 500 Hz) cochlear microphonics (CM) measurements are used to monitor hair-cell function and provide feedback to avert insertion trauma. However, it can be difficult to differentiate between trauma and the electrode’s progression through the cochlea when monitored with a single frequency. Multi-frequency CM measurements, while more complex to analyze, can provide more accurate feedback by measuring CM from various locations along the basilar membrane. Methods: A new algorithm was developed to analyze multi-frequency CM tracings by comparing amplitude and phase changes across different test frequencies. The new algorithm was evaluated as to its ability to identify drop-alarm instances with the multi-frequency approach, as compared to single-frequency 500 Hz tracings. Results: The algorithm presented in this manuscript uses the relationship between CM amplitude and phase changes across frequencies to provide real-time feedback during CI electrode placement. The results show that multi-frequency CM tracings raised an alarm only 0.5 times, as compared to 2.8 instances of alarm raised for the single-frequency 500 Hz CM measurements. Conclusions: Multi-frequency CM tracings can help reduce the number of alarms which may be false positives prompting unnecessary electrode manipulations, thereby minimizing the risk of insertion trauma.

Investigating the Effect of Blurring and Focusing Current in Cochlear Implant Users with the Panoramic ECAP Method.

For some cochlear implants (CIs), it is possible to focus electrical stimulation by partially returning current from the active electrode to nearby, intra-cochlear electrodes (partial tripolar (pTP) stimulation). Another method achieves the opposite: "blurring" by stimulating multiple electrodes simultaneously. The Panoramic ECAP (PECAP) method provides a platform to investigate their effects in detail by measuring electrically evoked compound action potentials and estimating current spread and neural responsiveness along the length of the CI electrode array. We investigate how sharpening and broadening the electrical current spread are reflected in PECAP estimates. PECAP measurements were recorded at most comfortable level in 12 ears of Advanced Bionics CI users. Focused thresholds were also determined. For the electrodes with the highest and lowest focused thresholds, additional PECAP measurements were recorded while stimulating in pTP mode and in "blurred" mode with 3 or 5 adjacent electrodes simultaneously stimulated. Current spread and neural responsiveness were then estimated along the electrode array using PECAP. PECAP revealed increased current spread estimates across participants for blurred stimulation of the targeted electrodes towards the apex of the cochlea. Variable results for pTP stimulation were found, with two of eight ears appearing to drive a small group-level effect of increased current spread. When stimulating multiple electrodes simultaneously, PECAP detected localized increases in current spread towards the apex (but not the base) of the cochlea. pTP stimulation showed mixed effects on PECAP current spread estimates. These findings are in line with behavioral speech perception studies and have implications for cochlear implant optimization.

Tinnitus Suppression with Electrical Stimulation at the Most Basal Contact of the Cochlear Implant Electrode as a Model for Round Window Stimulation.

The objective of this research was to test whether efficient tinnitus suppression could be achieved by electrical stimulation of the single most basal electrode contact of a cochlear implant. This approach simulates the effects of electrical stimulation using a round-window electrode. The study was performed in 10 adult cochlear implant patients showing complete or almost complete tinnitus suppression during electrical stimulation with their standard fitting-MAP. In all patients, tinnitus appeared again when the implant was switched off. Five Nucleus implant (1 CI532, 4 CI24RE CA) users and 5 Mi12xx series with FLEX28 electrodes with at least 6 months of CI experience were included. Two types of stimulation were presented at the most basal CI contact: a constant pulse train and a modulated pulse train. The variation in pulse rates was low rate (100-300 pps) and high (≥900 pps), and the current level ranged from the C-level to less than the T-level for both stimulation types. The effect of acute electrical stimulation at the most basal electrode contact was compared to the effect obtained with multichannel stimulation with the patient's current fitting MAP. Electrical stimulation was paused between tests with different stimulation types until tinnitus returned to baseline intensity. Patients reported Visual Analog Scale (VAS) scores for tinnitus loudness and intrusiveness during normal CI use and for each single contact stimulation type. Eight participants perceived complete suppression with one or more stimulation patterns. In 2 patients, suppression was less efficient than full-band CI stimulation. Louder stimuli are generally perceived as annoying and less effective in reducing tinnitus. In FLEX28 patients, it was also possible to obtain full tinnitus suppression with current amplitudes under the thresholds for auditory perception (this was not tested in patients with the Nucleus device). In 8 of the 10 included patients, we were able to obtain complete or almost complete tinnitus suppression with electrical stimulation at only 1 most basal electrode contact. Therefore, round-window stimulation with a single electrode may be a potential treatment for tinnitus in patients with significant residual hearing. The long-term effects of this therapy should be confirmed in future studies.

Molded Round Window Niche Implant as a Dexamethasone Delivery System in a Cochlear Implant-Trauma Animal Model.

Preserving residual hearing after cochlear implant (CI) surgery remains a crucial challenge. The application of dexamethasone (DEX) has been proven to positively affect residual hearing. To deliver DEX in a localized and controlled way, a round window niche implant (RNI), allowing drug diffusion via the round window membrane into the cochlea, may be used. To prove this concept, an RNI for guinea pigs as a CI-trauma model was manufactured by molding and tested for its drug release in vitro and biological effects in vivo. The RNIs were molded using silicone containing 10% DEX. Release was analyzed over time using high-performance liquid chromatography (HPLC). Fourteen adult guinea pigs were randomly assigned to two groups (CI or CI + RNI group). All animals received a unilateral CI electrode insertion trauma followed by CI insertion. The CI + RNI group was additionally implanted with an RNI containing 10% DEX. Animals were followed up for 4 weeks. Acoustically evoked auditory brainstem response and impedance measurement, micro-computed tomography (µCT) imaging, and histology were performed for evaluation. DEX was released for more than 250 days in vitro, with an initial burst followed by a slower release over time. Comparing the hearing threshold shift (from day 0 to day 28) of the CI and CI + RNI groups, significant differences were observed at 32 and 40 kHz. The impedance shift at basal contacts was lower in the CI + RNI group than in the CI group. Moreover, the fibrosis in the lower basal turn was reduced in the CI + RNI group in contrast to the CI group. The RNI containing 10% DEX has anti-inflammatory potential concerning fibrosis inhibition and has beneficial effects on hearing preservation at high frequencies.

The role of pressure and friction forces in automated insertion of cochlear implants.

Despite the success of cochlear implant (CI) surgery for hearing restoration, reducing CI electrode insertion forces is an ongoing challenge with the goal to further reduce post-implantation hearing loss. While research in this field shows that both friction and quasistatic pressure forces occur during CI insertion, there is a lack of studies distinguishing between these origins. The present study was conducted to analyze the contribution of both force phenomena during automated CI insertion. Five MED-EL FLEX28 CI electrode arrays were inserted into both a regular and uncoiled version of the same average scala tympani (ST). Both ST models had a pressure release hole at the apical end, which was kept open or closed to quantify pressure forces. ST models were filled with different sodium dodecyl sulfate (SDS) lubricants (1, 5, and 10% SDS, water). The viscosity of lubricants was determined using a rheometer. Insertions were conducted with velocities ranging from v= 0.125 mm/s to 2.0 mm/s. Viscosity of SDS lubricants at 20°C was 1.28, 1.96, and 2.51 mPas for 1, 5, and 10% SDS, respectively, which lies within the values reported for human perilymph. In the uncoiled ST model, forces remained within the noise floor (maximum: 0.049 × 10-3 N ± 1.5 × 10-3 N), indicating minimal contribution from quasistatic pressure. Conversely, forces using the regular, coiled ST model were at least an order of magnitude larger (minimum: Fmax = 28.95 × 10-3 N, v = 1 mm/s, 10% SDS), confirming that friction forces are the main contributor to total insertion forces. An N-way ANOVA revealed that both lubricant viscosity and insertion speed significantly reduce insertion forces (p < 0.001). For the first time, this study demonstrates that at realistic perilymph viscosities, quasistatic pressure forces minimally affect the total insertion force profile during insertion. Mixed friction is the main determinant, and significantly decreases with increaseing insertion speeds. This suggests that in clinical settings with similar ST geometries and surgical preparation, quasistatic pressure plays a subordinate role. Moreover, the findings indicate that managing the hydrodynamics of the cochlear environment, possibly through pre-surgical preparation or the use of specific lubricants, could effectively reduce insertion forces.

The Inter-Phase Gap Offset Effect as a Measure of Neural Health in Cochlear Implant Users With Residual Acoustic Hearing.

The inter-phase gap (IPG) offset effect is defined as the dB offset between the linear parts of electrically evoked compound action potential (ECAP) amplitude growth functions for two stimuli differing only in IPG. The method was recently suggested to represent neural health in cochlear implant (CI) users while being unaffected by CI electrode impedances. Hereby, a larger IPG offset effect should reflect better neural health. The aims of the present study were to (1) examine whether the IPG offset effect negatively correlates with the ECAP threshold and the preoperative pure-tone average (PTA) in CI recipients with residual acoustic hearing and (2) investigate the dependency of the IPG offset effect on hair cell survival and intracochlear electrode impedances. Seventeen adult study participants with residual acoustic hearing at 500 Hz undergoing CI surgery at the University Hospital of Zurich were prospectively enrolled. ECAP thresholds, IPG offset effects, electrocochleography (ECochG) responses to 500 Hz tone bursts, and monopolar electrical impedances were obtained at an apical, middle, and basal electrode set during and between 4 and 12 weeks after CI surgery. Pure-tone audiometry was conducted within 3 weeks before surgery and approximately 6 weeks after surgery. Linear mixed regression analyses and t tests were performed to assess relationships between (changes in) ECAP threshold, IPG offset, impedance, PTA, and ECochG amplitude. The IPG offset effect positively correlated with the ECAP threshold in intraoperative recordings (p < 0.001) and did not significantly correlate with the preoperative PTA (p = 0.999). The IPG offset showed a postoperative decrease for electrode sets that showed an ECochG amplitude drop. This IPG offset decrease was significantly larger than for electrode sets that showed no ECochG amplitude decrease, t(17) = 2.76, p = 0.014. Linear mixed regression analysis showed no systematic effect of electrode impedance changes on the IPG offset effect (p = 0.263) but suggested a participant-dependent effect of electrode impedance on IPG offset. The present study results did not reveal the expected relationships between the IPG offset effect and ECAP threshold values or between the IPG offset effect and preoperative acoustic hearing. Changes in electrode impedance did not exhibit a direct impact on the IPG offset effect, although this impact might be individualized among CI recipients. Overall, our findings suggest that the interpretation and application of the IPG offset effect in clinical settings should be approached with caution considering its complex relationships with other cochlear and neural health metrics.

Decreasing the physical gap in the neural-electrode interface and related concepts to improve cochlear implant performance.

Cochlear implants (CI) represent incredible devices that restore hearing perception for those with moderate to profound sensorineural hearing loss. However, the ability of a CI to restore complex auditory function is limited by the number of perceptually independent spectral channels provided. A major contributor to this limitation is the physical gap between the CI electrodes and the target spiral ganglion neurons (SGNs). In order for CI electrodes to stimulate SGNs more precisely, and thus better approximate natural hearing, new methodologies need to be developed to decrease this gap, (i.e., transitioning CIs from a far-field to near-field device). In this review, strategies aimed at improving the neural-electrode interface are discussed in terms of the magnitude of impact they could have and the work needed to implement them. Ongoing research suggests current clinical efforts to limit the CI-related immune response holds great potential for improving device performance. This could eradicate the dense, fibrous capsule surrounding the electrode and enhance preservation of natural cochlear architecture, including SGNs. In the long term, however, optimized future devices will likely need to induce and guide the outgrowth of the peripheral process of SGNs to be in closer proximity to the CI electrode in order to better approximate natural hearing. This research is in its infancy; it remains to be seen which strategies (surface patterning, small molecule release, hydrogel coating, etc.) will be enable this approach. Additionally, these efforts aimed at optimizing CI function will likely translate to other neural prostheses, which face similar issues.

Development and Evaluation of a Reusable, Force Measuring Tool for the Robot-Assisted Insertion of Cochlear Implant Electrode Arrays.

Limitations in human kinematics during cochlear implantation induce pressure transients and increased forces on intracochlear structures. Herein, we present a novel head-mounted surgical tool designed for the motorized insertion of cochlear implant electrode arrays. The tool integrates a force measurement feature to overcome the lack of haptic feedback in current robotic solutions. Utilizing a prototype device, we compare force measurements with those exerted on intracochlear structures in a realistic temporal bone model. Furthermore, we test the tool on six temporal bone specimens in a surgical setting to assess its performance in various anatomies. Force measurements exhibit good agreement with intracochlear forces, offering significantly improved resolution over manual, tactile sensing. Successful electrode array insertions in six cadaver specimens affirmed the feasibility of tool setup, motorized insertion and tool removal in different anatomies. The tool allows the robot-assisted insertion of cochlear implant electrode arrays and offers valuable insights during the surgical procedure, demonstrating promise for application in clinical contexts. This instrument has the potential to aid surgeons in achieving atraumatic placement of electrodes, consequently contributing to the improvement of hearing outcomes in cochlear implantation.

The Photon-Counting CT Enters the Field of Cochlear Implantation: Comparison to Angiography DynaCT and Conventional Multislice CT.

Cochlear duct length (CDL) measurement plays a role in the context of individualized cochlear implant (CI) surgery regarding an individualized selection and implantation of the CI electrode carrier and an efficient postoperative anatomy-based fitting process. The level of detail of the preoperative temporal bone CT scan depends on the imaging modality with major impact on CDL measurements and CI electrode contact position determination. The aim of this study was to evaluate the accuracy of perioperative CDL measurements and electrode contact determination in photon-counting CT (PCCT). Ten human fresh-frozen petrous bone specimens were examined with a first-generation PCCT. A clinically applicable radiation dose of 27.1 mGy was used. Scans were acquired before and after CI insertion. Postoperative measurement of the CDL was conducted using an otological planning software and 3D-curved multiplanar reconstruction. Investigation of electrode contact position was performed by two respective observers. Measurements were compared with a conventional multislice CT and to a high-resolution flat-panel volume CT with secondary reconstructions. Pre- and postoperative CDL measurements in PCCT images showed no significant difference to high-resolution flat-panel volume CT. Postoperative CI electrode contact determination was also as precise as the flat-panel CT-based assessment. PCCT and flat-panel volume CT were equivalent concerning interobserver variability. CDL measurement with PCCT was equivalent to flat-panel volume CT with secondary reconstructions. PCCT enabled highly precise postoperative CI electrode contact determination with substantial advantages over conventional multislice CT scanners.

Electrocochleography-Based Tonotopic Map: II. Frequency-to-Place Mismatch Impacts Speech-Perception Outcomes in Cochlear Implant Recipients.

Modern cochlear implants (CIs) use varying-length electrode arrays inserted at varying insertion angles within variably sized cochleae. Thus, there exists an opportunity to enhance CI performance, particularly in postlinguistic adults, by optimizing the frequency-to-place allocation for electrical stimulation, thereby minimizing the need for central adaptation and plasticity. There has been interest in applying Greenwood or Stakhovskaya et al. function (describing the tonotopic map) to postoperative imaging of electrodes to improve frequency allocation and place coding. Acoustically-evoked electrocochleography (ECochG) allows for electrophysiologic best-frequency (BF) determination of CI electrodes and the potential for creating a personalized frequency allocation function. The objective of this study was to investigate the correlation between early speech-perception performance and frequency-to-place mismatch. This retrospective study included 50 patients who received a slim perimodiolar electrode array. Following electrode insertion, five acoustic pure-tone stimuli ranging from 0.25 to 2 kHz were presented, and electrophysiological measurements were collected across all 22 electrode contacts. Cochlear microphonic tuning curves were subsequently generated for each stimulus frequency to ascertain the BF electrode or the location corresponding to the maximum response amplitude. Subsequently, we calculated the difference between the stimulus frequency and the patient's CI map's actual frequency allocation at each BF electrode, reflecting the frequency-to-place mismatch. BF electrocochleography-total response (BF-ECochG-TR), a measure of cochlear health, was also evaluated for each subject to control for the known impact of this measure on performance. Our findings showed a moderate correlation (r = 0.51; 95% confidence interval: 0.23 to 0.76) between the cumulative frequency-to-place mismatch, as determined using the ECochG-derived BF map (utilizing 500, 1000, and 2000 Hz), and 3-month performance on consonant-nucleus-consonant words (N = 38). Larger positive mismatches, shifted basal from the BF map, led to enhanced speech perception. Incorporating BF-ECochG-TR, total mismatch, and their interaction in a multivariate model explained 62% of the variance in consonant-nucleus-consonant word scores at 3 months. BF-ECochG-TR as a standalone predictor tended to overestimate performance for subjects with larger negative total mismatches and underestimated the performance for those with larger positive total mismatches. Neither cochlear diameter, number of cochlear turns, nor apical insertion angle accounted for the variability in total mismatch. Comparison of ECochG-BF derived tonotopic electrode maps to the frequency allocation tables reveals substantial mismatch, explaining 26.0% of the variability in CI performance in quiet. Closer examination of the mismatch shows that basally shifted maps at high frequencies demonstrate superior performance at 3 months compared with those with apically shifted maps (toward Greenwood and Stakhovskaya et al.). The implications of these results suggest that electrophysiological-based frequency reallocation might lead to enhanced speech-perception performance, especially when compared with conventional manufacturer maps or anatomic-based mapping strategies. Future research, exploring the prospective use of ECochG-based mapping techniques for frequency allocation is underway.

Comparison of 96-kV and 120-kV cone-beam CT for the assessment of cochlear implants

BackgroundTo compare the diagnostic value of 120-kV with conventional 96-kV Cone-Beam CT (CBCT) of the temporal bone after cochlear implant (CI) surgery.MethodsThis retrospective study included CBCT scans after CI surgery between 06/17 and 01/18. CBCT allowed examinations with 96-kV or 120-kV; other parameters were the same. Two radiologists independently evaluated following criteria on 5-point Likert scales: osseous spiral lamina, inner and outer cochlear wall, semi-circular canals, mastoid trabecular structure, overall image quality, metal and motion artefacts, depiction of intracochlear electrode position and visualisation of single electrode contacts. Effective radiation dose was assessed.ResultsSeventy-five patients (females, n = 39 [52.0%], mean age, 55.8 ± 16.5 years) were scanned with 96-kV (n = 32, 42.7%) and 120-kV (n = 43, 57.3%) protocols including CI models from three vendors (vendor A n = 7; vendor B n = 43; vendor C n = 25). Overall image quality, depiction of anatomical structures, and electrode position were rated significantly better in 120-kV images compared to 96-kV (all p < = 0.018). Anatomical structures and electrode position were rated significantly better in 120-kV CBCT for CI models from vendor A and C, while 120-kV did not provide improved image quality in CI models from vendor B. Radiation doses were significantly higher for 120-kV scans compared to 96-kV (0.15 vs. 0.08 mSv, p < 0.001).Conclusions120-kV and 96-kV CBCT provide good diagnostic images for the postoperative CI evaluation. While 120-kV showed improved depiction of temporal bone and CI electrode position compared to 96-kV in most CI models, the 120-kV protocol should be chosen wisely due to a substantially higher radiation exposure.

Electrochemical Degradation of Molecularly Imprinted Polymers for Future Applications of Inflammation Sensing in Cochlear Implants.

After cochlear implant (CI) insertion, there is a possibility of postoperative inflammation, which may involve proinflammatory markers such as interleukin-6. Detecting this inflammation promptly is crucial for administering anti-inflammatory drugs, if required. One potential method for detecting inflammation is using molecular imprinted polymers (MIPs). These MIPs, which can be deposited on the CI electrode, provide readout employing impedance measurements, a feature already available on the CI circuit. MIPs designed for this purpose should possess biocompatibility, conductivity, and degradability. The degradability is crucial because there is a limitation on the number of electrodes available, and once the inflammation sensor degrades after the acute inflammation period, it should remain usable as a regular electrode. In this work, conductive poly(3,4-ethylenedioxythiophene) polystyrenesulfonate-based MIPs were synthesized against biotin as a surrogate target marker. Specific biotin binding with MIPs was determined before and after degradation using electrochemical impedance spectroscopy (EIS) and compared with the control nonimprinted polymers (NIPs). Subsequently, MIPs were electrochemically degraded by EIS with different potentials, wherein a potential dependence was observed. With decreasing potential, fewer dissolved polymers and more monomer molecules were detected in the solution in which degradation took place. At a potential of 0.205 V a negligible amount of dissolved polymer in addition to the dissolved monomer molecules was measured, which can be defined as the limiting potential. Below this potential, only dissolved monomer molecules are obtained, which enables renal clearance. Biocompatibility testing revealed that both the polymer and the solution with dissolved monomer molecules do not exceed the ISO 10993-5 cytotoxicity threshold. Based on these findings, we have developed conductive, biocompatible, and controllably degradable MIPs capable of detecting biotin. This research work paves the way for the advancement of CIs, where inflammation can be detected using molecular imprinting technology without compromising the stability and biosafety of the product.

Understanding the impact of modiolus porosity on stimulation of spiral ganglion neurons by cochlear implants

Moderate-to-profound sensorineural hearing loss in humans is treatable by electrically stimulating the auditory nerve (AN) with a cochlear implant (CI). In the cochlea, the modiolus presents a porous bony interface between the CI electrode and the AN. New bone growth caused by the presence of the CI electrode or neural degeneration inflicted by ageing or otological diseases might change the effective porosity of the modiolus and, thereby, alter its electrical material properties. Using a volume conductor description of the cochlea, with the aid of a ‘mapped conductivity’ method and an ad-hoc ‘regionally kinetic’ equation system, we show that even a slight variation in modiolus porosity or pore distribution can disproportionately affect AN stimulation. Hence, because of porosity changes, an inconsistent CI performance might occur if neural degeneration or new bone growth progress after implantation. Appropriate electrical material properties in accordance with modiolar morphology and pathology should be considered in patient-specific studies. The present first-of-its-kind in-silico study advocates for contextual experimental studies to further explore the utility of modiolus porous morphology in optimising the CI outcome.

Optical method to preserve residual hearing in patients receiving a cochlear implant

IntroductionWorldwide, thousands of patients with severe to profound hearing loss restore their hearing with cochlear implant (CI) devices. Newer developments in electrode design and manufacturing and a better understanding of cochlear mechanics allow for conserving critical structures, often translating into serviceable residual hearing and improving device performance. Monitoring insertion speed and intraluminal pressure helps mitigate some of these challenges. However, the information becomes available after irreparable damage has occurred.MethodsWe developed and tested a high-resolution optical system to navigate the intricate anatomy of the cochlea during electrode insertion. The miniaturized optical system was integrated in conventional cochlear implants electrode arrays and custom-made cochlear probes. Electrode insertion were conducted in eight cadaveric human temporal bones and video recordings were acquired. Micro-computed tomography (μCT) scans were performed to evaluate the position of the modified electrode arrays.ResultsFull insertions of the modified CI electrode were successfully conducted and verified by μCT scans. Video recordings of the cochlear structures visible in scala tympani were acquired, and no scala migration was detected.DiscussionSurgeons can now follow the CI electrode's path during its insertion and reduce cochlear damage through early interventions and steering of the CI electrode. Our device will be compatible with robotic platforms that are already available to insert these electrodes.

Hampshire Sheep as a Large-Animal Model for Cochlear Implantation.

Sheep have been proposed as a large-animal model for studying cochlear implantation. However, prior sheep studies report that the facial nerve (FN) obscures the round window membrane (RWM), requiring FN sacrifice or a retrofacial opening to access the middle-ear cavity posterior to the FN for cochlear implantation. We investigated surgical access to the RWM in Hampshire sheep compared to Suffolk-Dorset sheep and the feasibility of Hampshire sheep for cochlear implantation via a facial recess approach. Sixteen temporal bones from cadaveric sheep heads (ten Hampshire and six Suffolk-Dorset) were dissected to gain surgical access to the RWM via an extended facial recess approach. RWM visibility was graded using St. Thomas' Hospital (STH) classification. Cochlear implant (CI) electrode array insertion was performed in two Hampshire specimens. Micro-CT scans were obtained for each temporal bone, with confirmation of appropriate electrode array placement and segmentation of the inner ear structures. Visibility of the RWM on average was 83% in Hampshire specimens and 59% in Suffolk-Dorset specimens (p = 0.0262). Hampshire RWM visibility was Type I (100% visibility) for three specimens and Type IIa (> 50% visibility) for seven specimens. Suffolk-Dorset RWM visibility was Type IIa for four specimens and Type IIb (< 50% visibility) for two specimens. FN appeared to course more anterolaterally in Suffolk-Dorset specimens. Micro-CT confirmed appropriate CI electrode array placement in the scala tympani without apparent basilar membrane rupture. Hampshire sheep appear to be a suitable large-animal model for CI electrode insertion via an extended facial recess approach without sacrificing the FN. In this small sample, Hampshire specimens had improved RWM visibility compared to Suffolk-Dorset. Thus, Hampshire sheep may be superior to other breeds for ease of cochlear implantation, with FN and facial recess anatomy more similar to humans.

Psychoacoustic and electroencephalographic responses to changes in amplitude modulation depth and frequency in relation to speech recognition in cochlear implantees

Temporal envelope modulations (TEMs) are one of the most important features that cochlear implant (CI) users rely on to understand speech. Electroencephalographic assessment of TEM encoding could help clinicians to predict speech recognition more objectively, even in patients unable to provide active feedback. The acoustic change complex (ACC) and the auditory steady-state response (ASSR) evoked by low-frequency amplitude-modulated pulse trains can be used to assess TEM encoding with electrical stimulation of individual CI electrodes. In this study, we focused on amplitude modulation detection (AMD) and amplitude modulation frequency discrimination (AMFD) with stimulation of a basal versus an apical electrode. In twelve adult CI users, we (a) assessed behavioral AMFD thresholds and (b) recorded cortical auditory evoked potentials (CAEPs), AMD-ACC, AMFD-ACC, and ASSR in a combined 3-stimulus paradigm. We found that the electrophysiological responses were significantly higher for apical than for basal stimulation. Peak amplitudes of AMFD-ACC were small and (therefore) did not correlate with speech-in-noise recognition. We found significant correlations between speech-in-noise recognition and (a) behavioral AMFD thresholds and (b) AMD-ACC peak amplitudes. AMD and AMFD hold potential to develop a clinically applicable tool for assessing TEM encoding to predict speech recognition in CI users.

Loudness Balancing Optimization for Better Speech Intelligibility, Music Perception, and Spectral Temporal Resolution in Cochlear Implant Users.

The behaviorally based programming with loudness balancing (LB) would result in better speech understanding, spectral-temporal resolution, and music perception scores, and there would be a relationship between these scores. Loudness imbalances at upper stimulation levels may cause sounds to be perceived as irregular, gravelly, or overly echoed and may negatively affect the listening performance of the cochlear implant (CI) user. LB should be performed after fitting to overcome these problems. The study included 26 unilateral Med-EL CI users. Two different CI programs based on the objective electrically evoked stapedial reflex threshold (P1) and the behaviorally program with LB (P2) were recorded for each participant. The Turkish Matrix Sentence Test (TMS) was applied to evaluate speech perception; the Random Gap Detection Test (RGDT) and Spectral-Temporally Modulated Ripple Test (SMRT) were applied to evaluate spectral temporal resolution skills; the Mini Profile of Music Perception Skills (mini-PROMS) and Melodic Contour Identification (MCI) tests were applied to evaluate music perception, and the results were compared. Significantly better scores were obtained with P2 in TMS tests performed in noise and quiet. SMRT scores were significantly correlated with TMS in quiet and noise, and mini-PROMS sound perception results. Although better scores were obtained with P2 in the mini-PROMS total score and MCI, a significant difference was found only for MCI. The data from the current study showed that equalization of loudness across CI electrodes leads to better perceptual acuity. It also revealed the relationship between speech perception, spectral-temporal resolution, and music perception.

Transimpedance Matrix Can Be Used to Estimate Electrode Positions Intraoperatively and to Monitor Their Positional Changes Postoperatively in Cochlear Implant Patients.

Accurate positioning of the electrode array during cochlear implant (CI) surgery is crucial for achieving optimal hearing outcomes. Traditionally, postoperative radiological imaging has been used to assess electrode position. Transimpedance matrix (TIM) measurements have also emerged as a promising method for assessing electrode position. This involves utilizing electric field imaging to create an electric distance matrix by analyzing voltage variations among adjacent electrodes. This study aimed to investigate the feasibility of using intraoperative TIM measurements to estimate electrode position and monitor postoperative changes. Retrospective cohort study. University Medical center, tertiary academic referral center. Patients undergoing CI (CI622) surgery between January 2019 and June 2022. CI electrode positions and maximal angular insertion depths (maxAID) were determined using X-ray imaging according to Stenvers' projection. The mean gradient phase (MGP) was extracted from the TIM, and a correlation between the MGP and maxAID was examined. A model was then built to estimate the maxAID using the MGP, and changes in electrode location over time were assessed using this model. Twenty-four patients were included in this study. A positive correlation between the maxAID and the MGP ( R = 0.7, p = 0.0001) was found. The established model was able to predict the maxAID with an accuracy of 27.7 ± 4.4°. Comparing intraoperative and postoperative TIM measurements, a decrease of 24.1° ± 10.7° in maxAID over time was observed. TIM measurements are useful for estimating the insertion depth of the electrode and monitoring changes in the electrode's position over time.

Patient and Device Factors Contributing to Electrically Evoked Stapedial Reflex Thresholds in Cochlear Implanted Adults

Introduction: Optimal cochlear implant (CI) outcomes are due to, at least in part, appropriate device programming. Objective measures, such as electrically evoked stapedial reflex thresholds (ESRTs), can be used to more accurately set programming levels. However, underlying factors that contribute to ESRT levels are not well understood. The objective of the current study was to analyze how demographic variables of patient sex and age, along with CI electrode location, influence ESRTs in adult CI recipients. Methods: A single institution retrospective review was performed. Electronic medical records, CI programming records, and clinic database of postoperative computerized tomography were reviewed to gather information regarding patient demographics, ESRTs, and electrode array metrics including medial-lateral distance and scalar location. Linear mixed models were constructed to determine how demographic variables and electrode position influence ESRTs recorded in 138 adult CI recipients. Results: ESRTs were significantly affected by recipient age, with older listeners demonstrating higher ESRT levels. On average, males had higher ESRT levels when compared to females. In a subset of the study sample, ESRT levels increased with increasing medial-lateral distance; however, there was not a statistically significant effect of electrode type (lateral/straight arrays compared to perimodiolar arrays). ESRTs were not affected by scalar location. Discussion/Conclusions: The results suggest that key demographic and electrode position characteristics influence the level of ESRTs in adult CI recipients. While ESRTs are widely used to assist with CI programming, underlying factors are not well understood. The significant factors of aging and sex could be due to middle ear mechanics or neural health differences. However, further data are needed to better understand these associations.

Electrically evoked auditory brainstem responses in deaf children with cochlear nerve canal stenosis

Background Deaf children with cochlear nerve canal stenosis (CNCs) are always considered poor candidates for cochlear implantation. Objectives To investigate the function of the peripheral auditory pathway in deaf children with CNCs, as revealed by the electrically evoked auditory brainstem response (EABR), and postoperative cochlear implants (CIs) outcomes. Materials and Methods Thirteen children with CNCs and 13 children with no inner ear malformations (IEMs) who received CIs were recruited. The EABR evoked by electrical stimulation from the CI electrode was recorded. Postoperative CI outcomes were assessed using Categories of Auditory Performance (CAP) and Speech Intelligibility Rate (SIR). Results Compared with children with no IEMs, children with CNCs showed lower EABR extraction rates, higher thresholds, a longer wave V (eV) latency and lower CAP and SIR scores. The auditory and speech performance was positively correlated with the diameter of the cochlear nerve canal and the number of channels showing wave III (eIII) and eV in children with CNCs. Conclusions and Significance The physiological function of the peripheral auditory pathway in children with CNCs is poorer than that in children with no IEMs. Postoperative auditory and speech abilities may depend on the severity of cochlear nerve malformation and auditory conduction function.