Electrically Evoked Auditory Brainstem Response Research Articles

Intraoperative EABR Testing Predicts Strength of Cochlear Implant Stimulation Optimized After Long-Term Use in Pediatric Malformation Ears.

This study focused on the intensities of cochlear implant (CI) stimulation in pediatric CI users with inner ear malformation or cochlear nerve deficiency (CND). In this population, CI programming is difficult because a large intensity of CI stimulation is required to achieve sufficient hearing, but the excess CI stimuli often induce facial nerve stimulation. We aimed to assess whether the results of intraoperative electrically evoked auditory brainstem responses (EABRs) testing predict maximum current levels of CI stimuli (cC levels) optimized by a behavioral-based method after long-term CI use. A retrospective case review. A tertiary referral CI center. A total of 116 ears with malformations (malformation group) and 63 control ears (control group) from patients younger than 18 years who received CI. The malformation group comprised 23 ears with a common cavity (CC), 26 with incomplete partition type 1 (IP-1), 26 with incomplete partition type 2 (IP-2), and 41 with CND. Diagnostic. Correlation between intraoperative EABR results and cC levels determined by the behavioral-based CI programming after long-term CI use. The CC, IP-1, and CND ears required significantly larger cC levels than the IP-2 ears and control groups. However, the cC levels increased to reach the plateau 1 year after surgery in all groups. Among the malformation group, 79 ears underwent intraoperative EABR testing. Greater than 80% of the CC, IP-1, and IP-2 ears and 54.8% of the CND ears exhibited evoked wave V (eV) and were included in the eV-positive category. Myogenic responses but no eV were observed in 18.2, 15.0, and 35.5% of the CC, IP-1, and CND ears, defined as the myogenic category. No eV or myogenic response was elicited in 9.7% of the CND ears. We focused on minimum current levels that elicited eV (eV levels) in the eV-positive category and maximum current levels that did not elicit any myogenic responses (myogenic levels) in the myogenic category. A significant relationship was detected between the eV levels and the cC levels. When analyzed in each malformation type, the eV levels significantly correlate with the cC levels in the CC and CND ears but not in the IP-1 and IP-2 ears, probably because of slight variation within the IP-1 group and the small number of the IP-2 group. The myogenic category did not show a significant relationship between the myogenic levels and cC levels, but the cC levels were similar to or smaller than the myogenic levels in most ears. This study confirmed that intraoperative EABR testing helps predict the optimal cC levels in malformation ears. EABR-based CI programming immediately after cochlear implantation, followed by behavioral-based CI programming, may allow us to achieve early postoperative optimization of CI maps even in young children with severe malformations.

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.

Electrically Evoked Auditory Brainstem Response Using Extracochlear Stimulation at Different Cochlear Sites: A Comparison With Intracochlear Stimulation.

The distribution and extent of excitable spiral ganglion neurons (SGNs) have been investigated using electrically evoked auditory brainstem response (EABR) during either pre- or perioperative period. In this study, we investigated the EABR with extracochlear stimulation (eEABR) as a preoperative testing tool to estimate these factors. Sixteen male Sprague-Dawley rats were used in this study. Experiments were conducted in 9 rats with normal hearing and 7 rats that were partially deafened with ouabain treatment. Each experiment involved the following steps in common: (1) The extracochlear stimulating electrode placement at three different sites along the axis of the cochlea and eEABR recordings. (2) Cochleostomies and 4-channel intracochlear array implantation. Then, EABR recordings with various electrode pair combinations. (3) After electrophysiological measurements, cochleae harvesting for histopathological evaluation. The slope characteristics of the amplitude growth function measured from eEABR and EABR, frequency-specific auditory thresholds, and the density of SGNs were compared. There were similar trends in slope changes on different sites of stimulation with both types of stimulation in normal hearing animals, a monotonically increasing slope with increasing distance between bipolar pairs. In addition, eEABR slopes showed significant correlations with EABR slopes when the expected cochlear regions of stimulation were similar in normal hearing animals. In partial-deaf animals, the auditory thresholds at several frequencies had a significant correlation to the eEABR slopes of each extracochlear electrode at the apical, middle, and basal cochlear positions. It showed that increasing stimulating regions of the cochlea revealed a differential effect on eEABR slopes according to the neural conditions. Our Results indicated that eEABR slopes showed significant spatial correlations to the functionality of the auditory nerve. Therefore, eEABR tests at various cochlear positions possibly can be used for estimating the extent of excitable SGNs in cochlear implant candidates prior to implantation.

Prediction of behavioral MCL using electrophysiological responses in children using MED-EL implant.

The present study aimed to correlate the various electrophysiological tests of ECAP, EABR and ESRT with programming parameters. If there is a correlation between them, fitting formulae to be derived to predict programming parameters. Further this fitting formula was validated on a clinical population. 22 children between age range of 5-12 years using MED-EL implant participated study. Electrophysiological tests of Electrically evoked compound Action Potential (ECAP), Electrical Evoked Stapedial Reflex Threshold (ESRT) and Electrically Evoked Auditory Brain Stem Responses (EABR) were measured on electrodes no 1,4, 8, and 11. Based on Pearson correlation analysis, there was a moderate correlation observed between each of electrophysiological tests with MCL level. Fitting formulae of ECAP with either ESRT or EABR were found to be accurately predict the MCL level. These fitting formulae were clinically validated on 6 children using Sonata implant with OPUS 2 processor. Two new programs with MCL were predicted using combination of ECAP with EABR and ECAP with ESRT as parameters in the fitting formulae. These programs were given to the participants to use for two weeks. Predicted MCLs were found to slightly higher (about 2qu to 5qu) than original MCL level. Reliability analysis indicated that the formulae predicted MCL with good accuracy. Speech perception and sound field thresholds were measured in the participants' Everyday program and two predicted programs. When ECAP & EABR were the parameters, the predicted program had improved audibility as reflected in sound field thresholds as compared to those obtained with other two programs. Based on Freidman test, the results indicated that significantly lower thresholds were found for both ECAP & EABR, or ECAP & ESRT based programs when compared to Everyday program. However, speech perception scores were not significantly different among the program as per Freidman test. Thus, both the fitting models were clinically validated. The findings imply that it is not always advisable to run all three electrophysiological testing to predict the MCL levels in clinical population. It would save lot of time to run just two tests to predict the MCL in difficult to test population.

Electrically evoked auditory responses: A classification for brainstem implant placement in Neurofibromatosis Type 2

ObjectiveIn auditory brainstem implant (ABI) surgery, array placement may be optimized by electrophysiological information of adequate brainstem activation gained from electrically evoked auditory brainstem responses (EABR). This study aims 1) to characterize in detail the EABR from ABI implantation, 2) to introduce an EABR Classification Scheme, and 3) to analyze data for their correlation with individual patients’ findings. MethodsOut of a continuous series of 54 patients who received an ABI between 2005 and 2019, 23 Neurofibromatosis Type 2 patients with complete documentation of 154 recordings were selected for offline analysis and for development and evaluation of a new EABR Classification Scheme comprising Class A: three vertex positive peaks, Class B:two peaks, Class C: a combination of one peak and a second melted double peak, Class D: one sole vertex positive peak and Class E: no peaks. ResultsAll 23 subjects showed EABR at final ABI position and experienced auditory sensations at first activation. The most frequent morphology consisted of two peaks, Classes B and C. Identified mean latencies were for P1 0.42 ms (±0.095), P2 1.42 ms (±0.244) and P3 2.41 ms (±0.329). Peak latencies correlated positively with tumor extensions (p < 0.005). ConclusionsThis study provides clear instructions on optimal EABR performance and evaluation. SignificanceThe new EABR Classification Scheme relies on a fast “online” identification of vertex positive peaks at the estimated post-artifact phase. The variability in EABR morphology provides an individual snapshot of the actual structural and functional status of the brainstem.

[Preliminary application of combined auditory monitoring technique in resection of vestibular neurinoma].

Objective: To explore the value of electrically evoked auditory brainstem response (EABR) monitoring combined with brainstem auditory evoked potential (BAEP) and compound action potential (CAP) monitoring during vestibular schwannoma resection for the protection of the cochlear nerve. Methods: Clinical data from 12 patients with vestibular schwannomas who had useful hearing prior to surgery were analyzed at the PLA General Hospital from January to December 2021. Among them, there were 7 males and 5 females, ranging in age from 25 to 59 years. Before surgery, patients underwent audiology assessments (including pure tone audiometry, speech recognition rate, etc.), facial nerve function evaluation, and cranial MRI. They then underwent vestibular schwannoma resection via the retrosigmoid approach. EABR, BAEP, and CAP were simultaneously monitored during surgery, and patients' hearing preservation was observed and analyzed after surgery. Results: Prior to surgery, the average PTA threshold of the 12 patients ranged from11 to 49 dBHL, with a SDS of 80% to 100%. Six patients had grade A hearing, and six patients had grade B hearing. All 12 patients had House-Brackman grade I facial nerve function prior to surgery. The MRI indicated tumor diameters between 1.1 and 2.4 cm. Complete removal was achieved in 10/12 patients, while near-total removal was achieved in 2/12 patients. There were no serious complications at the one-month follow-up after surgery. At the three-month follow-up, all 12 patients had House-Brackman grade I or II facial nerve function. Under EABR with CAP and BAEP monitoring, successful preservation of the cochlear nerve was achieved in six of ten patients (2 with grade B hearing, 3 with grade C hearing, and 1 with grade D hearing). Successful preservation of the cochlear nerve was not achieved in another four patients (all with grade D hearing). In two patients, EABR monitoring was unsuccessful due to interference signals; however, Grade C or higher hearing was successfully preserved under BAEP and CAP monitoring. Conclusion: The application of EABR monitoring combined with BAEP and CAP monitoring during vestibular schwannoma resection can help improve postoperative preservation of the cochlear nerve and hearing.

The effect of cochlear size on electrically evoked auditory brainstem responses in deaf children.

To investigate the relationship between auditory pathway function and cochlear size in deaf children with a radiologically normal inner ear or Mondini malformation. Thirty-five deaf children without inner ear malformations (IEMs) and forty cases with Mondini malformation were included in this study. The electrically evoked auditory brainstem responses (EABRs) evoked by electrical stimulation at the round window niche (RWN) and round window membrane (RWM) were recorded during cochlear implantation (CI) surgery. The anatomical parameters of the cochlea were assessed by high-resolution computed tomography and OTOPLAN 3-D construction software. Correlations between EABRs and cochlear sizes were analyzed. The EABR thresholds and/or latencies were negatively correlated with the basal cochlear diameter, cochlear width and/or cochlear duct length in both patients without IEMs and those with Mondini malformation. The physiological function of the peripheral auditory system depends on the anatomical structure of the cochlea to an extent. A larger cochlear size appears to be associated with better auditory conduction function. Our findings may be beneficial to selection of the proper electrode type and prediction of postoperative auditory rehabilitation. Level 4.

Electrically Evoked Auditory Brainstem Responses in Children Fitted with Hearing Aids Prior to Cochlear Implantation.

This study investigates the effect of hearing aid use on the peripheral auditory pathways in children with sensorineural hearing loss prior to cochlear implantation, as revealed by the electrically evoked auditory brainstem response (EABR). Forty children with hearing aids were recruited. Half of them had normal inner ear structures and the other half had inner ear malformations (IEMs). The EABR was evoked by electrically stimulating the round window niche (RWN) and round window membrane (RWM) during the cochlear implantation operation. The onset age of hearing aid use was significantly correlated with the peak latencies, but not amplitudes, of the wave III (eIII) and wave V (eV). Higher EABR thresholds were found for RWN stimulation than for RWM stimulation and in the children with IEMs than in those without IEMs. Our study provides neurophysiological evidence that earlier use of hearing aids may ameliorate physiological functions of the peripheral auditory pathway in children with and without IEMs. The EABR evoked by the electrical stimulation at RWM is more sensitive compared with that at RWN for evaluating functions of the auditory conduction pathway.

Evaluation of auditory pathway excitability using a pre-operative trans-tympanic electrically evoked auditory brainstem response under local anesthesia in cochlear implant candidates

Objective Subjective promontory stimulation is used to evaluate cochlear implant (CI) candidacy, but the test reliability is low. Electrically evoked auditory brainstem response (EABR) can verify the function of the auditory system objectively. This study’s procedure uses a trans-tympanic rounded bent-tip electrode to perform pre-operative EABR under local anaesthesia (LA-TT-EABR) using MED-EL Software and Hardware. This study aimed to determine usability and effectiveness for CI candidates. Design We hypothesised that LA-TT-EABR waveforms of good quality would be related to successful hearing outcomes. We assumed that the duration of hearing loss/deafness was a confounding factor to study outcomes. Study sample 19 borderline CI candidates. Results Positive LA-TT-EABR results were confirmed in 14 patients. LA-TT-EABR’s mean latency was 2.05 ± 0.31 ms (eII/eIII) and 4.24 ± 0.39 ms (eIV/eV). Latencies weren’t statistically different from intra-operative EABR elicited by basal CI contacts. All positive LA-TT-EABR patients benefitted from CI and speech performance improved one year after implantation. One patient with negative LA-TT-EABR was cochlear-implanted and had no hearing sensation. Conclusions LA-TT-EABR is a tool in the frame of pre-operative objective testing the auditory pathway. It seems useful for clinical testing CI candidacy. Based on this study’s outcomes, LA-TT-EABR should be recommended for uncertain CI candidates.

Evaluation of auditory pathway by EABR before cochlear implantation and the postoperative effect analysis.

To investigate the evaluation value of electrically evoked auditory brainstem response (EABR) monitoring before cochlear implantation in patients with cochlear nerve defects (CND). A total of 54 patients with cochlear nerve defects who underwent cochlear implantation in our hospital from 2011 to 2018 were selected as the CND group, and 20 patients with normal cochlear implantation were selected as the control group. The preoperative audiological characteristics, EABR characteristics and follow-up neural response telemetry results of the two groups were retrospectively analysed, and the preoperative EABR threshold and initiation C value were subjected to linear regression and correlation analysis. The EABR waveform of the CND group was significantly different from the control group in terms of average wave V threshold, average dynamic range and V-wave I/O curve slope (P < 0.05). Average C value and dynamic range had a statistically significant difference from the control group (P < 0.05). Statistically significant positive correlations were found between the EABR threshold and C value, wave V I/O slope and postoperative category of auditory perception (P < 0.05). The EABR test can be used to evaluate the auditory pathway function before cochlear implantation and its postoperative effect in patients with CND.

P 19 Auditory brainstem implants: Intraoperative electrophysiological measures and hearing outcome

Introduction: Auditory brainstem implants (ABI) are primarily designed for tumour related deafness in neurofibromatosis type 2 (NF2) patients. These neuro-prosthetic devices bypass the auditory nerve and produce hearing sensations by direct stimulation of the cochlear nuclei (CN). This study investigates the importance of intraoperative electrically evoked auditory brainstem responses (EABR) with regards to the auditory outcome. Patients & Methods: Out of a prospectively collected series of ABI implantations from 2005 to 2019, 22 patients (11 male, 11 female) fulfilled inclusion criteria (min. age of 15 y, NF2 diagnosis) and were analysed retrospectively for EABR and hearing outcome. EABR analysis relied on the presence and number of vertex positive peaks P1, P2 and P3 at brainstem stimulation. For post-operative hearing outcome a new Clinical ABI Outcome Classification was developed and applied at 6 to 12 months containing 4 categories: Category 1, Star Performer, with >80% speech understanding in auditory only MTP (mono- to polysyllabic) test and ability for continuous spoken conversation without any lip reading; Category 2, Good Performer, with >40 to 80% in auditory only MTP test and some speech understanding combined with lip reading; Category 3, Useful Performance, communication with some additional measures possible (hearing, lip-reading and written notes); Category 4, Non-useful Performance, no or only scarce sound reception. Results: In 22 patients, 146 EABR recordings at various sites of the implant were evaluated: A three-peak-formation was present in 7, a two-peek-formation in 115 (78,8%), and one-peak in 13 EABRs, while 11 remained without any reproducible responses. EABR waveforms showed some variation: Peak P1 developed just out of or after the stimulus artefact while peaks P2 and P3 sometimes showed melting and larger latency differences. P1 appears to correspond to wave III of the acoustically evoked ABR. Overall auditory outcome was useful (Categories 1, 2 or 3) in 95,5% of cases, with Star or Good Performance in about 77% of patients. EABR presence predicted auditory rehabilitation correctly in 95,5%. Conclusion: False positive EABR are rare and a matter of open discussion such as on lead dislocation or secondary brainstem nuclei degeneration. Overall, intra-operative reproducible EABR are highly predictive of adequate brainstem activation and useful hearing rehabilitation with ABI in deaf NF2 patients and appear indispensable for implant positioning. The most reliable peak P1 of EABR may represent immediate activity of cochlear nuclei. The importance of further peaks P2 and P3 and their anatomic correlation still need further evaluation and possibly correlation with more long-term auditory development. The presented ABI hearing classification includes the internationally accepted MTP test but goes beyond this and proves to be a universal tool to elucidate the patient's capacity for speech communication in real life.

Electrically evoked auditory brainstem responses in deaf patients with Mondini malformation during cochlear implantation.

To investigate the auditory pathway functions in deaf patients with Mondini malformation using the electrically evoked auditory brainstem response (EABR) during cochlear implantation (CI). A total of 58 patients with severe to profound sensorineural hearing loss (SNHL) were included in this study. Of these patients, 27 cases had Mondini malformation and 31 control cases had no inner ear malformations (IEMs). Intraoperative EABRs evoked by electrical stimulation at the round window niche (RWN) and round window membrane (RWM) were recorded. Patients with Mondini malformation showed significantly lower EABR extraction rates than those with no IEMs did. However, for patients who showed EABRs, no significant difference in EABR thresholds, wave III (eIII) latencies, wave V (eV) latencies or eIII-eV latency intervals was found between two groups. The physiological functions of the peripheral auditory system in patients with Mondini malformation may divide into opposite extremes, as revealed by a robust EABR and the absence of the EABR, respectively. The auditory conduction function should be objectively and individually evaluated for patients with Mondini malformation by the EABR.

Outcome of Cochlear Implantation in Children with Auditory Neuropathy-A Dual Case Study

Objectives: The aim of this study is to compare the outcome of cochlear implantation in two pediatric auditory neuropathy cases. Methods: Two cases with auditory neuropathy were taken. Case 1 was 10 year old male. Case 2 was 11 year old male. In preoperative assessment both have bilateral severe to profound sensory-neural hearing loss. Case 1 was implanted by MED-EL using sonata Ti100 opus 2 processor. Case 2 was implanted using MED-EL using sonata Ti100 opus 2 processor. Both cases were given auditory verbal therapy. Both cases attended auditory verbal therapy for a period of 2 years. In postoperative assessment for each individual subject, electrically evoked compound action potentials (ECAPs), electrically evoked stapedius reflex threshold (ESRT), and electrically evoked auditory brainstem response (EABR) thresholds were determined. The following questionnaire extended receptive expressive emergent language scale (E-REELS) , Categories of Auditory Performance (CAP) score, Speech Intelligibility Rating (SIR) scale, Meaningful Auditory-Integration Scale (MAIS) and Meaningful Use of Speech Scale (MUSS) are scales were administered. Results: In the postoperative assessment, ECAP, ESRT, EABR, MUSS, MAIS shows that case 1 with auditory neuropathy have better performance than case 2. Conclusion: It is essential that all possible complications and postoperative performance should be considered in cochlear implantation for auditory neuropathy individuals

Bilateral EABR stimulating mode testing bilateral CI patients refecting binaural integration:a preliminary study

ObjectiveTo analyze binaural integration, we used a new stimulation mode of the electrically evoked auditory brainstem response (EABR), to reflect bilaterally implanted cochlear function. DesignEABR was tested using the following procedure: First, both ears were evaluated separately, with the contralateral speech processor closed (C), followed by another measurement with both processors open (O). Subsequently, the eV latencies and amplitudes were assessed. The Speech, Spatial, and Qualities of Hearing Scale (SSQ), Categories of auditory performance (CAP) and speech intelligibility rating (SIR) scores were used to assess binaural hearing ability subjectively. Study sampleFifteen subjects with bilateral CI from 1997 to 2018 were recruited, each diagnosed with severe to profound hearing loss. ResultsAll SSQ scores, except for one, were greater than six (the exception scored 1.3/0.8/1.0). All CAP/SIR scores except one were greater than 6/4 (the exception scored 0/1). All patients exhibited good quality EABR measurements. The open contralateral processor significantly reduced the eV latency while enhancing the eV amplitude compared to monaural stimulation. The objective EABR results were consistent with subjective speech perception and auditory ability assessed using the SSQ scale. ConclusionThe EABR accurately reflected auditory pathway maturation and development after CI; thus, reflecting accordance with subjective speech and hearing performances. Furthermore, bilateral CI facilitates binaural integration and auditory brainstem plasticity.

Characteristics of electrically evoked auditory brainstem response in children with large vestibular aqueduct syndrome after cochlear implantation

Background The vestibular aqueduct (VA) width may affect the auditory conduction pathway of large vestibular aqueduct syndrome (LVAS) children. Objective Analyzing the electrically evoked auditory brainstem response (EABR) after cochlear implantation (CI) in severe to profound sensorineural hearing loss (SNHL) children with LVAS. Materials and methods Fifty-four children with SNHL who received CI were selected, including 21 children with LVAS and 33 children without inner ear malformations (IEMs). The VA width was measured in LVAS children. The post-operative EABRs were recorded in all children. Results For the LVAS group, the VA width was positively correlated with wave III (eIII) latency of EABR at the No. 2 electrode (E2), E5, E8, and E11, the VA width was positively correlated with wave V (eV) latency of EABR at E2, E5, E8, and E11. Only the eV latency of E2 showed a significant difference between the two groups. Conclusion and significance SNHL children with LVAS and no IEMs have similar conduction of the auditory pathway. In the LVAS group, the conduction of the auditory pathway becomes better with the decrease of VA width. Rational use of post-operative EABRs and the measurement of anatomical parameters can effectively assess the development of part auditory pathways in LVAS children, which may be helpful in predicting post-operative speech and hearing recovery.

Design of a Bone-Guided Cochlear Implant Microsystem With Monopolar Biphasic Multiple Stimulations and Evoked Compound Action Potential Acquisition and Its In Vivo Verification

A CMOS bone-guided cochlear implant (BGCI) microsystem is proposed and verified. In the implanted System on Chip (SoC) of the proposed BGCI, the evoked compound action potential (ECAP) acquisition and electrode–tissue impedance measurement (EAEIM) circuit is integrated to measure both ECAP and electrode–tissue impedance for clinical diagnoses. Both positive-/negative-voltage charge pumps and monopolar biphasic constant-current stimulation (CCS) stimulator are designed on-chip to realize monopolar biphasic CCS or double-electrode multiple stimulations with a maximum stimulation current of 1.2 mA and a step of 10 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mu \text{A}$ </tex-math></inline-formula> . With the double-electrode multiple stimulations, the electric field can be shifted and localized under the stimulating electrode to stimulate the auditory nerves. The wireless bilateral data telemetry circuits with a full-wave active rectifier and the pulsed load-shift keying (PLSK) modulators/demodulators are designed for power and data transmission. <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">In vivo</i> animal tests on guinea pigs have shown that the Wave III of electrically evoked auditory brainstem responses (EABRs) can be evoked successfully by electrical stimulation. Moreover, the decreasing latency gradient of evoked Wave III has been measured under the double-electrode multiple stimulations where the location of peak electric field can be shifted to the stimulating electrode in the apical site to stimulate the auditory nerves. Thus, the desired frequency resolution and spatial specificity of stimulation can be achieved. Both electrical measurement and <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">in vivo</i> animal tests have verified that the proposed BGCI microsystem is a feasible solution to eliminate the symptoms for patients with high-frequency hearing loss.

EABR THR Estimation Using High-Rate Multi-Pulse Stimulation in Cochlear Implant Users.

We estimated the electrically-evoked auditory brainstem response thresholds (eABR THRs) in response to multi-pulses with high burst rate of 10,000 pulses-per-second (pps). Growth functions of wave eV amplitudes, root mean square (RMS) values, peak of phase-locking value (PLV), and the lowest valid data point (LVDP) were calculated in 1-, 2-, 4-, 8-, and 16-pulses conditions. The growth functions were then fitted and extrapolated with linear and exponential functions to find eABR THRs. The estimated THRs were compared to psychophysical THRs determined for multi-pulse conditions as well as to the clinical THRs measured behaviorally at the rate of 1,000 pps. The growth functions of features showed shallower growth slopes when the number of pulses increased. eABR THRs estimated in 4-, 8-, and 16-pulses conditions were closer to the clinical THRs, when compared to 1- and 2-pulses conditions. However, the smallest difference between estimated eABR THRs and clinical THRs was not always achieved from the same number of pulses. The smallest absolute difference of 30.3 μA was found for the linear fittings on growth functions of eABR RMS values in 4-pulses condition. Pearson’s correlation coefficients (PCCs) between eABR THRs and psychophysical THRs were significant and relatively large in all but 16-pulses conditions. The PCCs between eABR THRs and clinical THRs, however, were smaller and in less cases significant. Results of this study showed that eABRs to multi-pulse stimulation could, to some extent, represent clinical stimulation paradigms, and thus in comparison to single pulses, could estimate clinical THRs with smaller errors.

Development of a chronically-implanted mouse model for studies of cochlear health and implant function

Mice with chronic cochlear implants can significantly contribute to our understanding of the relationship between cochlear health and implant function because of the availability of molecular tools for controlling conditions in the cochlea and transgenic lines modeling human disease. To date, research in implanted mice has mainly consisted of short-term studies, but since there are large changes in implant function following implant insertion trauma, and subsequent recovery in many cases, longer-term studies are needed to evaluate function and perception under stable conditions. Because frequent anesthetic administration can be especially problematic in mice, a chronic model that can be tested in the awake condition is desirable. Electrically-evoked compound action potentials (ECAPs) recorded with multichannel cochlear implants are useful functional measures because they can be obtained daily without anesthesia. In this study, we assessed changes and stability of ECAPs, electrically-evoked auditory brainstem responses (EABRs), ensemble spontaneous activity (ESA), and impedance data over time after implanting mice with multichannel implants. We then compared these data to histological findings in these implanted cochleae, and compared results from this chronic mouse model to data previously obtained in a well-established chronically-implanted guinea pig model. We determined that mice can be chronically implanted with cochlear implants, and ECAP recordings can be obtained frequently in an awake state for up to at least 42 days after implantation. These recordings can effectively monitor changes or stability in cochlear function over time. ECAP and EABR amplitude-growth functions (AGFs), AGF slopes, ESA levels and impedances in mice with multichannel implants appear similar to those found in guinea pigs with long-term multichannel implants. Animals with better survival of spiral ganglion neurons (SGNs) and inner hair cells (IHCs) have steeper AGF slopes, and larger ESA responses. The time course of post-surgical ear recovery may be quicker in mice and can show different patterns of recovery which seem to be dependent on the degree of insertion trauma and subsequent histological conditions. Histology showed varying degrees of cochlear damage with fibrosis present in all implanted mouse ears and small amounts of new bone in a few ears. Impedance changes over time varied within and across animals and may represent changes over time in multiple variables in the cochlear environment post-implantation. Due to the small size of the mouse, susceptibility to stress, and the higher potential for implant failure, chronic implantation in mice can be challenging, but overall is feasible and useful for cochlear implant research.

Temporal integration of short-duration pulse trains in cochlear implant listeners: Psychophysical and electrophysiological measurements

While electrically-evoked auditory brainstem response (eABR) thresholds for low-rate pulse trains correlate well with behavioral thresholds measured at the same rate, the correlation is much weaker with behavioral thresholds measured at high rates, such as used clinically. This implies that eABRs to low-rate stimuli cannot be reliably used for objective programming of threshold levels in cochlear implant (CI) users. Here, we investigate whether the use of bunched-up pulses (BUPS), consisting of groups of closely-spaced pulses may be used as an alternative stimulus.Experiment 1 measured psychophysical detection thresholds for several stimuli having a period of 32 ms in nine CI subjects implanted with a Med-EL device. The stimuli differed in the number of pulses present in each period (from 1 to 32), the pulse rate within period (1000 pps and as high as possible for BUPS) and the electrode location (apical or basal). The correlation between psychophysical thresholds obtained for a high-rate (1000 pps) clinical stimulus and for the BUPS stimuli increased as the number of pulses per period of BUPS increased from 1 to 32. This first psychophysical experiment suggests that the temporal processes affecting the threshold of clinical stimuli are also present for BUPS.Experiment 2 measured eABRs on the apical electrode of eight CI subjects for BUPS having 1, 2, 4, 8, 16 or 32 pulses per period. For most subjects, wave V was visible for BUPS having up to 16 pulses per period. The latency of wave V at threshold increased as a function of the number of pulses per period, suggesting that the eABR reflects the integration of multiple pulses at such low levels or that the neural response to each individual pulse increases along the sequence due to facilitation processes. There was also a strong within-subject correlation between electrophysiological and behavioral thresholds for the different BUPS stimuli. This demonstrates that the drop in behavioral threshold obtained when increasing the number of pulses per period of the BUPS can be measured electrophysiologically using eABRs. In contrast, the across-subject correlation between eABR thresholds for BUPS and clinical thresholds remained relatively weak and did not increase with the number of pulses per period. Implications of the use of BUPS for objective programming of CIs are discussed.

EABR measurements during cochlear implantation in one-year-old, infant, child, adult, and elderly patients

Background Clinical application of electrically-evoked intracochlear auditory brainstem responses (eABRs) for evaluation of brainstem maturity or aging changes has not been well investigated. Aim/objective We compare the eV latencies of intraoperative eABR measurements in one-year-olds, infants, children, adults, and the elderly, with the goal of investigating the changes in the brainstem auditory pathway due to development and aging. Materials and methods We studied 58 ears of 51 patients who underwent cochlear implantation between 2013 and 2019 using MED-EL’s Concerto or Synchrony implants with Flex28 or Flex soft electrodes. EABRs were recorded during cochlear implantation. The stimuli were delivered by the MED-EL Maestro to the apical, middle, and basal turn electrodes at stimulus levels 1000, 800, and 600 cu, with a pulse width of 30 µs. Results In eABRs recorded from electrodes installed at both the mastoid and nape, there was no difference in latency between age groups within each stimulus level. Conclusion and significance ABR latency was not affected by development after age one and aging of the brainstem auditory pathway. Our study will be useful as a control in identifying abnormal eABR wave configurations in patients with cochlear malformations, cochlear nerve deficiencies, or auditory neuropathy, regardless of age.