Modeling the relationship between psychophysical perception and electrically evoked compound action potential threshold in young cochlear implant recipients: clinical implications for implant fitting

Is the spread of excitation different between adults and children cochlear implants users?

PURPOSE

While cochlea is adult size at birth, etiologies and bone density may differ between children and adults. Differences in neural response thresholds (tNRT) and the spread of excitation (SOE) width may impact the use of artificial intelligence algorithms in speech processor fitting.

AIM

To identify whether neural response telemetry threshold and spread of excitation width are similar in adults and children.

METHODS

Retrospective cross-sectional study approved by the Ethical Board. Intraoperative tNRT and SOE recordings of consecutive cochlear implant surgeries in adults and children implanted with Cochlear devices (Cochlear™, Australia) were selected. SOE was recorded on electrode 11 (or adjacent, corresponding to the medial region of the cochlea) through the standard forward-masking technique in Custom Sound EP software, which provides SOE width in millimeters. Statistical comparison between adults and children was performed using the Mann-Whitney test (p ≤ 0.05).

RESULTS

Of 1282 recordings of intraoperative evaluations, 414 measurements were selected from children and adults. Despite the tNRT being similar between adults and children, SOE width was significantly different, with lower values in children with perimodiolar arrays. Besides, it was observed that there is a difference in the electrode where the SOE function peak occurred, more frequently shifted to electrode 12 in adults implanted. In straight arrays, there was no difference in any of the parameters analyzed on electrode 11.

CONCLUSION

Although eCAP thresholds are similar, SOE measurements differ between adults and children in perimodiolar electrodes.

Correlation between neural response telemetry measurements and fitting levels

INTRODUCTION

The neural response telemetry (NRT) is a standard procedure in cochlear implantation mostly used to determine the functionality of implanted device and to check auditory nerve responds to the stimulus. Correlation between NRT measurements and subjective threshold (T) and maximum comfort (C) levels has been reported but results are inconsistent, and it is still not clear which of the NRT measurements could be the most useful in predicting fitting levels.

PURPOSE

In our study we aimed to investigate which NRT measurement corresponds better to fitting levels. Impedance (IMP), Evoked Action Potential (ECAP) threshold and amplitude growth function (AGF) slope values were included in the study. Also, we tried to identify cochlear area at which the connection between NRT measurements and fitting levels would be the most pronounced.

MATERIALS AND METHODS

Thirty-one children implanted with Cochlear device were included in this retrospective study. IMP, ECAP thresholds and AGF were obtained intra-operatively and 12 months after surgery at electrodes 5, 11 and 19 as representative for each part of cochlea. Subjective T and C levels were obtained 12 months after the surgery during cochlear fitting.

RESULTS

ECAP thresholds obtained 12 months after surgery showed statistically significant correlation to both T and C levels at all 3 selected electrodes. IMP correlated with C levels while AGF showed tendency to correlate with T levels. However, these correlations were not statistically significant for all electrodes.

CONCLUSION

ECAP threshold measurements correlated to T and C values better than AGF slope and IMP. Measurements obtained twelve months after surgery seems to be more predictive of T and C values compared to intra-operative measurements. The best correlation between ECAP threshold and T and C values was found at electrode 11 suggesting NRT measurements at mid-portion cochlear region to be the most useful in predicting fitting levels.

Experienced Adult Cochlear Implant Users Show Improved Speech Recognition When Target Fitting Parameters Are Applied

OBJECTIVES

The aim of the present study was to investigate whether prediction models built by de Graaff et al. (2020) can be used to improve speech recognition in experienced adult postlingual implanted Cochlear CI users. de Graaff et al. (2020) found relationships between elevated aided thresholds and a not optimal electrical dynamic range (<50 CL or >60 CL), and poorer speech recognition in quiet and in noise. The primary hypothesis of the present study was that speech recognition improves both in quiet and in noise when the sound processor is refitted to match targets derived from the prediction models from de Graaff et al. (2020). A second hypothesis was that subjectively, most of the CI users would find the new setting too loud because of an increase in C levels, and therefore, prefer the old settings.

DESIGN

A within-participant repeated measures design with 18 adult Cochlear CI users was used. T- and C-levels were changed to "optimized settings," as predicted by the model of de Graaff et al. (2020). Aided thresholds, speech recognition in quiet, and speech recognition in noise were measured with the old settings and after a 4-week acclimatization period with the optimized settings. Subjective benefit was measured using the Device Oriented Subjective Outcome Scale questionnaire.

RESULTS

The mean electrical dynamic range changed from 41.1 (SD = 6.6) CL to 48.6 (SD = 3.0) CL. No significant change in aided thresholds was measured. Speech recognition improved for 16 out of 18 participants and remained stable for 2 participants. Average speech recognition scores in quiet significantly improved by 4.9% (SD = 3.8%). No significant change for speech recognition in noise was found. A significant improvement in subjective benefit was found for one of the Device Oriented Subjective Outcome subscales (speech cues) between the old and optimized settings. All participants chose to keep the optimized settings at the end of the study.

CONCLUSIONS

We were able to improve speech recognition in quiet by optimizing the electrical dynamic range of experienced adult CI users, according to the prediction models built by de Graaff et al. (2020). There was no significant change in aided thresholds nor in speech recognition in noise. The findings of the present study suggest that improved performance for speech recognition in quiet in adult Cochlear CI users can be achieved by setting the dynamic range as close as possible to values between 50 and 60 CL when the volume level is at 10.

Comparisons of electrophysiological and psychophysical fitting methods for cochlear implants

OBJECTIVE

This study compared two different versions of an electrophysiology-based software-guided cochlear implant fitting method with a procedure employing standard clinical software. The two versions used electrically evoked compound action potential (ECAP) thresholds for either five or all twenty-two electrodes to determine sound processor stimulation level profiles. Objective and subjective performance results were compared between software-guided and clinical fittings.

DESIGN

Prospective, double-blind, single-subject repeated-measures with permuted ABCA sequences.

STUDY SAMPLE

48 post linguistically deafened adults with ≤15 years of severe-to-profound deafness who were newly unilaterally implanted with a Nucleus device.

RESULTS

Speech recognition in noise and quiet was not significantly different between software- guided and standard methods, but there was a visit/learning-effect. However, the 5-electrode method gave scores on the SSQ speech subscale 0.5 points lower than the standard method. Clinicians judged usability for all methods as acceptable, as did subjects for comfort. Analysis of stimulation levels and ECAP thresholds suggested that the 5-electrode method could be refined.

CONCLUSIONS

Speech recognition was not inferior using either version of the electrophysiology-based software-guided fitting method compared with the standard method. Subject-reported speech perception was slightly inferior with the five-electrode method. Software-guided methods saved about 10 min of clinician's time versus standard fittings.

Accessing the stapedius muscle via novel surgical retrofacial approach during cochlear implantation surgery: Intraoperative results on feasibility and safety

Human stapedius muscle (SM) can be directly and safely accessed via retrofacial approach, opening new approaches to directly measure the electrically evoked stapedius reflex threshold (eSRT). The measurement of the SM activity via direct surgical access represents a potential tool for objective eSRT fitting of cochlear implants (CI), increasing the benefit experienced by the CI users and leading to new perspectives in the development of smart implantable neurostimulators. 3D middle-ear reconstructions created after manual segmentation and related SM accessibility metrics were evaluated before the CI surgery for 16 candidates with assessed stapedius reflex. Retrofacial approach to access the SM was performed after facial recess exposure. In cases of poor exposition of SM, the access was performed anteriorly to the FN via drilling of the pyramidal eminence (PE). The total access rate of the SM via both the retrofacial and anterior approach of the FN was 100%. In 81.2% of cases (13/16), the retrofacial approach allowed to access the SM on previously categorized well exposed (8/8), partially exposed (4/5), and wholly concealed (1/3) SM with respect to FN. Following intraoperative evaluation in the remaining 18.8% (3/16), the SM was accessed anteriorly via drilling of the PE. Exposure of SM with respect to the FN and the sigmoid sinus’s prominence was a predictor for the suitable surgical approach. The retrofacial approach offers feasible and reproducible access to the SM belly, opening direct access to electromyographic sensing of the eSRT. Surgical planner tools can quantitatively assist pre-surgical assessment.

Remote Intraoperative Neural Response Telemetry: Technique and Results in Cochlear Implant Surgery

OBJECTIVE

Present results with remote intraoperative neural response telemetry (NRT) during cochlear implantation (CI) and its usefulness in overcoming the inefficiency of in person NRT.

STUDY DESIGN

Case series.

SETTING

Tertiary academic otology practice.

PATIENTS

All patients undergoing primary or revision CI, both adult and pediatric, were enrolled.

INTERVENTIONS

Remote intraoperative NRT performed by audiologists using a desktop computer to control a laptop in the operating room. Testing was performed over the hospital network using commercially available software. A single system was used to test all three FDA-approved manufacturers' devices.

MAIN OUTCOME MEASURES

Success rate and time savings of remote NRT.

RESULTS

Out of 254 procedures, 252 (99.2%) underwent successful remote NRT. In two procedures (0.7%), remote testing was unsuccessful, and required in-person testing to address technical issues.Both failed attempts were due to hardware failure (OR laptop or headpiece problems). There was no relation between success of the procedure and patient/surgical factors such as difficult anatomy, or the approach used for inner ear access. The audiologist time saved using this approach was considerable when compared with in-person testing.

CONCLUSIONS

Remote intraoperative NRT testing during cochlear implantation can be performed effectively using standard hardware and remote-control software. Especially important during the Covid-19 pandemic, such a procedure can reduce in-person contacts, and limit the number of individuals in the operating room. Remote testing can provide additional flexibility and efficiency in audiologist schedules.

Maximum acceptable level for the determination of ECAP and ESRT in a paediatric population

OBJECTIVES

Two of the most used objective measures are electrically evoked action potentials (ECAPs) and electrically evoked stapedius reflex thresholds (ESRTs). Although stimuli used for these measures differ considerably, both measures are influenced by subjective loudness percept. We focus on the subjective maximum acceptable loudness (MAL) to investigate if loudness sensitivity varied along the electrode array during ECAP recordings. In addition, we explored how the MAL reached during an ECAP recording related to the postoperative ESRT.

METHODS

Uni- and bilaterally implanted young CI users (n = 15, average age = 9 y, age range 3-18 y) underwent ECAP and ESR recordings using the clinical software MAESTRO (MED-EL, Innsbruck, Austria) and a commercially available immittance instrument (PATH MEDICAL GmbH, Germering, Germany).

RESULTS

Loudness tolerance during ECAP recordings was lowest at the two apical-most electrode contacts (number 1 and 2). There was a moderate correlation between the MAL achieved during ECAP recordings and ESR maximum stimulation amplitudes. (r: 0.44344).

CONCLUSIONS

ECAP recordings should commence at basal or medial contacts to increase the users' comfort and loudness tolerance, especially in young CI users. A higher maximum stimulation appears to increase the chance of the automatic determination of ECAP thresholds for all electrode contacts.

Effect of Increasing Pulse Phase Duration on Neural Responsiveness of the Electrically Stimulated Cochlear Nerve

OBJECTIVES

The aim of this study is to (1) investigate the effects of increasing the pulse phase duration (PPD) on the neural response of the electrically stimulated cochlear nerve (CN) in children with CN deficiency (CND) and (2) compare the results from the CND population to those measured in children with normal-sized CNs.

DESIGN

Study participants included 30 children with CND and 30 children with normal-sized CNs. All participants used a Cochlear Nucleus device in the test ear. For each subject, electrically evoked compound action potential (eCAP) input/output (I/O) functions evoked by single biphasic pulses with different PPDs were recorded at three electrode locations across the electrode array. PPD durations tested in this study included 50, 62, 75, and 88 μsec/phase. For each electrode tested for each study participant, the amount of electrical charge corresponding to the maximum comfortable level measured for the 88 μsec PPD was used as the upper limit of stimulation. The eCAP amplitude measured at the highest electrical charge level, the eCAP threshold (i.e., the lowest level that evoked an eCAP), and the slope of the eCAP I/O function were measured. Generalized linear mixed effect models with study group, electrode location, and PPD as the fixed effects and subject as the random effect were used to compare these dependent variables measured at different electrode locations and PPDs between children with CND and children with normal-sized CNs.

RESULTS

Children with CND had smaller eCAP amplitudes, higher eCAP thresholds, and smaller slopes of the eCAP I/O function than children with normal-sized CNs. Children with CND who had fewer electrodes with a measurable eCAP showed smaller eCAP amplitudes and flatter eCAP I/O functions than children with CND who had more electrodes with eCAPs. Increasing the PPD did not show a statistically significant effect on any of these three eCAP parameters in the two subject groups tested in this study.

CONCLUSIONS

For the same amount of electrical charge, increasing the PPD from 50 to 88 μsec for a biphasic pulse with a 7 μsec interphase gap did not significantly affect CN responsiveness to electrical stimulation in human cochlear implant users. Further studies with different electrical pulse configurations are warranted to determine whether evaluating the eCAP sensitivity to changes in the PPD can be used as a testing paradigm to estimate neural survival of the CN for individual cochlear implant users.

[Threshold dynamics of the auditory nerve electrically evoked compound action potential in implanted children]

OBJECTIVE

To study the dynamics of thresholds of the electrically evoked compound action potential of the auditory nerve (ECAP) during neural responce telemetry (NRT) intraoperatively, at the time of activation of the cochlear implantation system (CI) and after 3 and 6 months.

MATERIAL AND METHODS

The study included 50 children aged 1 year to 4 years with bilateral sensorineural deafness, operated on by Nucleus CI512 Profile + CP900 CI systems («Cochlear», Australia). In all patients, the electrode array was fully inserted. The dynamics and thresholds of ECAP were recorded and assessed in dynamics: when performing NRT intraoperatively, when the CI system was activated, and after 3 and 6 months. To assess the thresholds, the 1st, 6th, 11th, 16th and 22nd electrodes of the multichannel electrode array were selected.

RESULTS

The average threshold values and the NRT threshold profile determined intraoperatively and during measurements at different times after the activation of the CI system were significantly different (p<0.001), while the average postoperative results were characterized by relative stability. It was shown that the thresholds determined on the electrodes located in the middle of the electrode lattice are more stable than the thresholds determined on the apical and basal electrodes. In most patients, the NRT threshold values determined at the time of the activation of the CI system and after 3 and 6 months were significantly lower than the thresholds determined intraoperatively. The data obtained allow us to conclude that NRT is a stable and accurate technique that allows you to objectify the process of setting up an individual card for the stimulation of the speech processor at the rehabilitation stage after cochlear implantation.

Efficacy of using NRT thresholds in cochlear implants fitting, in prelingual pediatric patients

Objective

To evaluate the efficacy of using neural response telemetry (NRT) thresholds in predicting behavioural thresholds during programming of cochlear implant in prelingual children.

Method

Prospective study of 28 cochlear implants implanted with Nucleus 24 cochlear implant. We recorded NRT-thresholds on electrode numbers 1, 6, 11, 16 and 22 of the electrode array in each patient, the neural response thresholds were correlated with the behavioural map after six months of programming the device.

Results

The mean neural response telemetry level was significantly higher than the mean threshold level (T-level) but lower than the comfortable level (C-level) in all the electrodes tested. NRT levels could statistically significantly predict T behavioural levels and comfortable behavioural levels, p < 0.01. There was a strong positive correlation between comfortable thresholds and neural response telemetry level measurements and behavioural threshold level and neural response telemetry threshold measurements.

Conclusion

There is a useful role for neural response telemetry values in predicting the behavioural threshold and comfortable values in prelingual children. Combining the NRT values with behavioural observations can improve the programming of cochlear implants.

Test/Retest Variability of the eCAP Threshold in Advanced Bionics Cochlear Implant Users

The reliability of the electrically evoked compound action potential (eCAP) threshold depends on its precision and accuracy. The precision of the eCAP threshold reflects its variability, while the accuracy of the threshold shows how close it is to the actual value. The objective of this study was to determine the test/retest variability of the eCAP threshold in Advanced Bionics cochlear implant users, which has never been reported before. We hypothesized that the test/retest variability is dependent on the presence of random noise in the recorded eCAP waveforms. If this holds true, the recorded error should be reduced by approximately the square-root of the number of averages. As secondary objectives, we assessed the effects of the slope of the amplitude growth function (AGF), cochlear location, and eCAP threshold on eCAP threshold precision. We hypothesized that steeper slopes should result in better precision of the linearly extrapolated eCAP threshold. As other studies have shown that apical regions have steeper slopes and larger eCAPs, we recorded eCAPs in three different cochlear locations. The difference of the precision between two commonly applied stimulus-artifact reduction paradigms on eCAP threshold precision was compared, namely averaging of alternating stimulus polarities (AP averaging) and forward masking (FM). FM requires the addition of more waveforms than AP averaging, and hence we expected FM to have lower precision than AP.

[Evoked potentials in the rehabilitation of the patients after cochlear implantation]

The objective methods for the hearing examination of the patients after cochlear implantation provide an important tool for the speech processor fitting. The aim of the present study was to evaluate the possibilities and the informative value of the electrically evoked compound action potential (ECAP) and electrically evoked auditory brainstem response (EABR) combined recording technique. For this reason, the comparison of the ECAP and EABR thresholds with comfortable levels of stimulation, obtained on the basis of subjective response and psychophysical testing of the patients with good results after cochlear implantation was performed. 19 patients with the CI experience from 1 to 5 years were included in our study. The combined registration of ECAP and EABR can be used to evaluate the functional capacity of the central auditory pathways and for the fitting of the complicated patients, especially those in whom the registration proved impossible with the use of other objective techniques. The ECAP and EABR threshold values were well correlated with the individual stimulation map profiles in the patients with the CI experience of less than two years (p<0.05). The results obtained in the present study allow us to conclude that combined registration of ECAP and EABR could be used for the determination of stimulation comfort level parameters and individual stimulation map profiles, especially in combination with the minimum amount of psychoacoustic information received from the patient.

Electrical dynamic range is only weakly associated with auditory performance and speech recognition in long-term users of cochlear implants

OBJECTIVE

The electrical dynamic range (EDR) has been suggested to be related to auditory performance in cochlear implant (CI) users. However, few reports have evaluated postlingual CI users who have used CIs for long periods in comparison with prelingual CI users. Here, we evaluated auditory perception and speech performance in terms of the EDR in long-term CI users. The EDR, and auditory and speech performances, were compared between pre- and post-lingual CI users.

METHODS

We enrolled all patients who received CIs from April 2000 to December 2010 at Seoul National University Hospital, and who had ≥5 years of experience with CIs. The EDRs affording subjective responses at the threshold level (T-level) and comfortable level (C-level) were analyzed in terms of their relationships with pure tone audiometry levels, speech evaluation scores, including those on the Phonetically Balanced (PB) Word List test, vowel and consonant tests, a sentence test, and the Korean version of the Central Institute for the Deaf (K-CID) test; we also calculated Category in Auditory Performance (CAP) scores.

RESULTS

We found no significant difference in the average EDR, CAP, K-CID, PB word, consonant, or vowel scores between pre- and post-lingual CI users. The EDR was weakly associated with the PB word (P = 0.003, r = 0.462) and consonant scores (P = 0.005, r = 0.438). Other speech evaluations, such as the CAP, K-CID, and vowel scores, were not significantly associated with the EDR T-level. We found no association between pure tone thresholds at 0.5, 1, or 2 kHz, and the speech evaluation scores or EDRs of low-, middle-, or high-frequency channels.

CONCLUSIONS

The EDR was only weakly associated with speech performance, such as scores on consonant and PB word tests in long-term CI users, irrespective of pre- or post-lingual deafness status.

Electrically-evoked auditory steady-state responses as neural correlates of loudness growth in cochlear implant users

Loudness growth functions characterize how the loudness percept changes with current level between the threshold and most comfortable loudness level in cochlear implant users. Even though loudness growth functions are highly listener-dependent, currently default settings are used in clinical devices. This study investigated whether electrically-evoked auditory steady-state response amplitude growth functions correspond to behaviorally measured loudness growth functions. Seven cochlear implant listeners participated in two behavioral loudness growth tasks and an EEG recording session. The 40-Hz sinusoidally amplitude-modulated pulse trains were presented to CI channels stimulating at a more apical and basal region of the cochlea, and were presented at different current levels encompassing the listeners' dynamic ranges. Behaviorally, loudness growth was measured using an Absolute Magnitude Estimation and a Graphic Rating Scale with loudness categories. A good correspondence was found between the response amplitude functions and the behavioral loudness growth functions. The results are encouraging for future advances in individual, more automatic, and objective fitting of cochlear implants.

Using Electrically-evoked Compound Action Potentials to Estimate Perceptive Levels in Experienced Adult Cochlear Implant Users

HYPOTHESIS

The cochlear implant (CI) fitting level prediction accuracy of electrically-evoked compound action potential (ECAP) should be enhanced by the addition of demographic data in models.

INTRODUCTION

No accurate automated fitting of CI based on ECAP has yet been proposed.

METHODS

We recorded ECAP in 45 adults who had been using MED-EL CIs for more than 11 months and collected the most comfortable loudness level (MCL) used for CI fitting (prog-MCL), perception thresholds (meas-THR), and MCL (meas-MCL) measured with the stimulation used for ECAP recording. Linear mixed models taking into account cochlear site factors were computed to explain prog-MCL, meas-MCL, and meas-THR.

RESULTS

Cochlear region and ECAP threshold were predictors of the three levels. In addition, significant predictors were the ECAP amplitude for the prog-MCL and the duration of deafness for the prog-MCL and the meas-THR. Estimations were more accurate for the meas-THR, then the meas-MCL, and finally the prog-MCL.

CONCLUSION

These results show that 1) ECAP thresholds are more closely related to perception threshold than to comfort level, 2) predictions are more accurate when the inter-subject and cochlear regions variations are considered, and 3) differences between the stimulations used for ECAP recording and for CI fitting make it difficult to accurately predict the prog-MCL from the ECAP recording. Predicted prog-MCL could be used as bases for fitting but should be used with care to avoid any uncomfortable or painful stimulation.

The Electrically Evoked Compound Action Potential: From Laboratory to Clinic

The electrically evoked compound action potential (eCAP) represents the synchronous firing of a population of electrically stimulated auditory nerve fibers. It can be directly recorded on a surgically exposed nerve trunk in animals or from an intra-cochlear electrode of a cochlear implant. In the past two decades, the eCAP has been widely recorded in both animals and clinical patient populations using different testing paradigms. This paper provides an overview of recording methodologies and response characteristics of the eCAP, as well as its potential applications in research and clinical situations. Relevant studies are reviewed and implications for clinicians are discussed.

Auditory steady state responses and cochlear implants: Modeling the artifact-response mixture in the perspective of denoising

Auditory steady state responses (ASSRs) in cochlear implant (CI) patients are contaminated by the spread of a continuous CI electrical stimulation artifact. The aim of this work was to model the electrophysiological mixture of the CI artifact and the corresponding evoked potentials on scalp electrodes in order to evaluate the performance of denoising algorithms in eliminating the CI artifact in a controlled environment. The basis of the proposed computational framework is a neural mass model representing the nodes of the auditory pathways. Six main contributors to auditory evoked potentials from the cochlear level and up to the auditory cortex were taken into consideration. The simulated dynamics were then projected into a 3-layer realistic head model. 32-channel scalp recordings of the CI artifact-response were then generated by solving the electromagnetic forward problem. As an application, the framework’s simulated 32-channel datasets were used to compare the performance of 4 commonly used Independent Component Analysis (ICA) algorithms: infomax, extended infomax, jade and fastICA in eliminating the CI artifact. As expected, two major components were detectable in the simulated datasets, a low frequency component at the modulation frequency and a pulsatile high frequency component related to the stimulation frequency. The first can be attributed to the phase-locked ASSR and the second to the stimulation artifact. Among the ICA algorithms tested, simulations showed that infomax was the most efficient and reliable in denoising the CI artifact-response mixture. Denoising algorithms can induce undesirable deformation of the signal of interest in real CI patient recordings. The proposed framework is a valuable tool for evaluating these algorithms in a controllable environment ahead of experimental or clinical applications.

Analysis of electrically evoked compound action potential of the auditory nerve in children with bilateral cochlear implants

Introduction

The cochlear implant device has the capacity to measure the electrically evoked compound action potential of the auditory nerve. The neural response telemetry is used in order to measure the electrically evoked compound action potential of the auditory nerve.

Objective

To analyze the electrically evoked compound action potential, through the neural response telemetry, in children with bilateral cochlear implants.

Methods

This is an analytical, prospective, longitudinal, historical cohort study. Six children, aged 1–4 years, with bilateral cochlear implant were assessed at five different intervals during their first year of cochlear implant use.

Results

There were significant differences in follow-up time (p = 0.0082) and electrode position (p = 0.0019) in the T-NRT measure. There was a significant difference in the interaction between time of follow-up and electrode position (p = 0.0143) when measuring the N1-P1 wave amplitude between the three electrodes at each time of follow-up.

Conclusion

The electrically evoked compound action potential measurement using neural response telemetry in children with bilateral cochlear implants during the first year of follow-up was effective in demonstrating the synchronized bilateral development of the peripheral auditory pathways in the studied population.

The importance of electrically evoked stapedial reflex in cochlear implant

Introdução

A determinação da área dinâmica do implante coclear é um dos procedimentos mais importantes em sua programação. O uso de medidas objetivas, em especial a do limiar do reflexo estapédico evocado eletricamente, pode contribuir para a definição deste campo, principalmente em crianças ou em indivíduos com múltiplos comprometimentos, pois fornecem valores específicos que servem como base no início da programação do implante coclear.

Objetivo

Verificar por meio de uma revisão a utilização do limiar do reflexo estapédico evocado ele- tricamente durante o processo de ativação e de mapeamento do implante coclear. Métodos: Levantamento bibliográfico nas plataformas Pubmed e Bireme e nas bases de dados MedLine, LILACS e SciELO, com buscas padronizadas até setembro de 2012, utilizando-se palavras-chave. Para a seleção e avaliação dos estudos científicos levantados, foram estabelecidos critérios, contemplando os seguintes aspectos: autor, ano/local, grau de recomendação/nível de evidência científica, objetivo, amostra, faixa etária, média de idade em anos, testes avaliativos, resultados e conclusão.

Resultados

Dos 7.304 artigos encontrados, 7.080 foram excluídos pelo título, 152 pelo resumo, 17 pela leitura do artigo, 43 eram repetidos e 12 foram selecionados para o estudo. Conclusão: O reflexo estapédico evocado eletricamente é capaz de auxiliar na programação do implante coclear, principalmente em pacientes que apresentam respostas inconsistentes.

© 2014 Associação Brasileira de Otorrinolaringologia e Cirurgia Cérvico-Facial. Publicado por Elsevier Editora Ltda. Todos os direitos reservados.

Can ECAP measures be used for totally objective programming of cochlear implants?

An experiment was conducted with eight cochlear implant subjects to investigate the feasibility of using electrically evoked compound action potential (ECAP) measures other than ECAP thresholds to predict the way that behavioral thresholds change with rate of stimulation, and hence, whether they can be used without combination with behavioral measures to determine program stimulus levels for cochlear implants. Loudness models indicate that two peripheral neural response characteristics contribute to the slope of the threshold versus rate function: the way that neural activity to each stimulus pulse decreases as rate increases and the slope of the neural response versus stimulus current function. ECAP measures related to these two characteristics were measured: the way that ECAP amplitude decreases with stimulus rate and the ECAP amplitude growth function, respectively. A loudness model (incorporating temporal integration and the two neural response characteristics) and regression analyses were used to evaluate whether the ECAP measures could predict the average slope of the behavioral threshold versus current function and whether individual variation in the measures could predict individual variation in the slope of the threshold function. The average change of behavioral threshold with increasing rate was well predicted by the model when using the average ECAP data. However, the individual variations in the slope of the thresholds versus rate functions were not well predicted by individual variations in ECAP data. It was concluded that these ECAP measures are not useful for fully objective programming, possibly because they do not accurately reflect the neural response characteristics assumed by the model, or are measured at current levels much higher than threshold currents.

Neural response telemetry reconsidered: I. The relevance of ECAP threshold profiles and scaled profiles to cochlear implant fitting

OBJECTIVE

For more than a decade, Neural Response Telemetry (NRT) has provided direct access to the electrically evoked compound action potential (ECAP) as elicited by the Nucleus cochlear implant. When used clinically during fitting, ECAP threshold profiles are applied by shifting the profile to the audible threshold and comfort level boundaries (the T- and C-level profiles, respectively). The resulting profiles, to date, have matched the curvature of the ECAP threshold profile exactly. When compared with psychophysical profiles, previous studies have shown that this approach incurs errors in program levels that are no better than flat or population mean profiles. However, C-level profiles are observed to be flatter than T-level profiles. Accordingly, ECAP threshold profiles are flattened in this study when applied at increasing stimulus levels, and the effectiveness of this approach is evaluated among other methods.

DESIGN

In phase I, ECAP thresholds (via AutoNRT) and T- and C-levels were measured from 15 adult Nucleus Freedom implantees. Psychophysical levels were measured using pulse train stimuli at six different stimulation rates, spanning 80 to 3500 Hz. The different rates spread T- and C-levels across a range of stimulus levels. At each of these levels, a scaling factor of best fit was calculated such that the shifted ECAP threshold profile, when scaled (0 giving a flat profile, 1 giving an unmodified profile), gave the best fit to the corresponding psychophysical profile. From the 148 such T- and C-level profiles, a single profile scaling model was determined by a simple linear regression. In phase II, the model was tested on data using three separate stimulation rates (250, 900, and 2400 Hz) and 14 additional subjects. The root mean square psychophysical level mismatch of the ECAP threshold profile, the scaled ECAP threshold profile, a flat profile, and a mean population profile was calculated per subject and per stimulation rate, and the differences in the means of these calculations were compared. In phase III, 13 separate subjects evaluated the scaled ECAP-based program during a 2 wk trial, comparing the new program to a flat program and a conventional ECAP-based program with unmodified ECAP threshold profiles. A questionnaire captured their subjective preferences.

RESULTS

In phase I, the profile scaling model constructed from the data prescribed a flattening of the ECAP threshold profile with increasing mean T- or C-level (in CL units): scale = 1.38 - 0.0043 PsychoMean. In phase II, the scaled ECAP-based profiles were found to fit the psychophysical profiles significantly better in all test configurations (typically of the order of 5% dynamic range) compared with all other profiles. In phase III, 62% of subjects preferred the scaled ECAP-based program, whereas 8% preferred the conventional ECAP-based program, 15% the flat program and 15% had no preference. Analyses of the questionnaires revealed significantly higher ratings for the scaled ECAP-based programs, whereas the conventional ECAP-based programs were not rated differently than the flat programs.

CONCLUSIONS

The scaled ECAP threshold profile method provides a clinically significant enhancement to ECAP-based fitting methods, confirming the value of the ECAP threshold profile to cochlear implant fitting.

Correlation between NRT measurement level and behavioral levels in pediatrics cochlear implant patients

OBJECTIVE

To determine the relationship between the electrically evoked nerve action potential (Neural Response Telemetry [NRT]) and behavioral levels (T- and C-level) for pediatric patients using the Nucleus 24 cochlear implant system.

METHOD

A hospital based study of pediatric cochlear implant patients in the period between June 2000 and December 2008. At King Abdul-Aziz University Hospital (KAUH) Saudi Arabia the Neural Response Telemetry was administered to 47 children (mean age at implantation: 4 years) with the Nucleus 24 cochlear implants. Four intra cochlear electrodes (numbers 5, 10, 15, and 20) were tested one-month post-implantation, the neural response threshold compared with the behavioral threshold and the maximum comfort level estimated at the same time.

RESULTS

At all the electrode numbers, the mean for NRT level measurements was significantly higher than that for the T-level measurements and the mean for the C-level measurements was significantly higher than that for NRT level measurements The correlation analyses showed positive correlation between C-level and NRT level measurements and T-level and NRT level measurements.

CONCLUSION

There was a positive correlation between NRT value measurements and both T and C value measurements. Therefore, it is useful to use the NRT values to predict the behavioral T and C values in prelingual children.

Advances in cochlear implant telemetry: evoked neural responses, electrical field imaging, and technical integrity

During the last decade, cochlear implantation has evolved into a well-established treatment of deafness, predominantly because of many improvements in speech processing and the controlled excitation of the auditory nerve. Cochlear implants now also feature telemetry, which is highly useful to monitor the proper functioning of the implanted electronics and electrode contacts. Telemetry can also support the clinical management in young children and difficult cases where neural unresponsiveness is suspected. This article will review recent advances in the telemetry of the electrically evoked compound action potential that have made these measurements simple and routine procedures in most cases. The distribution of the electrical stimulus itself sampled by "electrical field imaging" reveals general patterns of current flow in the normal cochlea and gross abnormalities in individual patients; models have been developed to derive more subtle insights from an individual electrical field imaging. Finally, some thoughts are given to the extended application of telemetry, for example, in monitoring the neural responses or in combination with other treatments of the deaf ear.

Efeitos do potencial de ação neural sobre a percepção de fala em usuários de implante coclear

O Potencial de Ação Composto Evocado Eletricamente reflete a atividade do nervo auditivo, podendo ser registrado através dos eletrodos do implante coclear. A determinação dos elementos neurais estimuláveis pode contribuir para explicar a variabilidade de desempenho entre indivíduos implantados. OBJETIVO: Comparar o desempenho nos testes de percepção da fala entre pacientes que apresentaram e que não apresentaram potencial de ação composto evocado eletricamente no momento intra-operatório. MATERIAL E MÉTODO: Estudo prospectivo no qual 100 indivíduos usuários do implante coclear Nucleus 24 foram divididos em dois grupos de acordo com a presença ou ausência do potencial de ação intra-operatório. Após 6 meses de uso do dispositivo, os resultados dos testes de percepção de fala foram comparados entre os grupos. RESULTADOS: O potencial foi observado em 72% dos pacientes. A percepção no teste de frases em formato aberto foi melhor nos indivíduos com presença de potencial (média 82,8% contra 41,0%, p = 0,005). Houve associação entre ausência do potencial e etiologia da surdez por meningite. CONCLUSÃO: Ausência de potencial neural intraoperatório esteve associada ao pior desempenho na percepção da fala e à etiologia da surdez por meningite. Por outro lado, a presença do potencial de ação intraoperatório sugere ótimo prognóstico.

Auditory brainstem activity and development evoked by apical versus basal cochlear implant electrode stimulation in children

OBJECTIVE

The role of apical versus basal cochlear implant electrode stimulation on central auditory development was examined. We hypothesized that, in children with early onset deafness, auditory development evoked by basal electrode stimulation would differ from that evoked more apically.

METHODS

Responses of the auditory nerve and brainstem, evoked by an apical and a basal implant electrode, were measured over the first year of cochlear implant use in 50 children with early onset severe to profound deafness who used hearing aids prior to implantation.

RESULTS

Responses at initial stimulation were of larger amplitude and shorter latency when evoked by the apical electrode. No significant effects of residual hearing or age were found on initial response amplitudes or latencies. With implant use, responses evoked by both electrodes showed decreases in wave and interwave latencies reflecting decreased neural conduction time through the brainstem. Apical versus basal differences persisted with implant experience with one exception; eIII-eV interlatency differences decreased with implant use.

CONCLUSIONS

Acute stimulation shows prolongation of basally versus apically evoked auditory nerve and brainstem responses in children with severe to profound deafness. Interwave latencies reflecting neural conduction along the caudal and rostral portions of the brainstem decreased over the first year of implant use. Differences in neural conduction times evoked by apical versus basal electrode stimulation persisted in the caudal but not rostral brainstem.

SIGNIFICANCE

Activity-dependent changes of the auditory brainstem occur in response to both apical and basal cochlear implant electrode stimulation.

Influence of Evoked Compound Action Potential on Speech Perception in Cochlear Implant Users

Electrically Evoked Compound Action Potential is a measure of synchronous cochlear nerve fibers activity elicited by electrical stimulation of the cochlear implant. The electrophysiological nerve responses may contribute to explain the variability in individual performance of cochlear implant recipients.

Aim

To compare speech perception tests’ performances of cochlear implant users according to the presence or absence of intraoperative neural telemetry responses.

Material and Method

Prospective study design with 100 “Nucleus 24” cochlear implant users divided in two groups according to the presence or absence of intraoperative neural telemetry responses. Speech perception tests were performed after 6 months of continuous use of the device and compared among groups.

Results

Intraoperative action potentials were observed in 72 % of individuals. Open-set sentence test results were better in implant users who had neural telemetry responses when compared to implant users in whom this potential was absent (averages 82.8 % versus 41 %, p = 0.005). There was a strong association between post meningitis-related deafness and absence of intraoperative potentials.

Conclusion

The absence of intraoperative neural telemetry responses was associated with worse performances in speech perception tests and meningitis as etiology of deafness. On the other hand, the presence of these potentials suggests excellent prognosis.

AutoNRT™: An automated system that measures ECAP thresholds with the Nucleus® Freedom™ cochlear implant via machine intelligence

OBJECTIVE

AutoNRT is an automated system that measures electrically evoked compound action potential (ECAP) thresholds from the auditory nerve with the Nucleus Freedom cochlear implant. ECAP thresholds along the electrode array are useful in objectively fitting cochlear implant systems for individual use. This paper provides the first detailed description of the AutoNRT algorithm and its expert systems, and reports the clinical success of AutoNRT to date.

METHODS

AutoNRT determines thresholds by visual detection, using two decision tree expert systems that automatically recognise ECAPs. The expert systems are guided by a dataset of 5393 neural response measurements. The algorithm approaches threshold from lower stimulus levels, ensuring recipient safety during postoperative measurements. Intraoperative measurements use the same algorithm but proceed faster by beginning at stimulus levels much closer to threshold. When searching for ECAPs, AutoNRT uses a highly specific expert system (specificity of 99% during training, 96% during testing; sensitivity of 91% during training, 89% during testing). Once ECAPs are established, AutoNRT uses an unbiased expert system to determine an accurate threshold. Throughout the execution of the algorithm, recording parameters (such as implant amplifier gain) are automatically optimised when needed.

RESULTS

In a study that included 29 intraoperative and 29 postoperative subjects (a total of 418 electrodes), AutoNRT determined a threshold in 93% of cases where a human expert also determined a threshold. When compared to the median threshold of multiple human observers on 77 randomly selected electrodes, AutoNRT performed as accurately as the 'average' clinician.

CONCLUSIONS

AutoNRT has demonstrated a high success rate and a level of performance that is comparable with human experts. It has been used in many clinics worldwide throughout the clinical trial and commercial launch of Nucleus Custom Sound Suite, significantly streamlining the clinical procedures associated with cochlear implant use.

The pattern of auditory brainstem response wave V maturation in cochlear-implanted children

OBJECTIVE

Maturation of acoustically evoked brainstem responses (ABR) in hearing children is not complete at birth but rather continues over the first two years of life. In particular, it has been established that the decrease in ABR wave V latency can be modeled as the sum of two decaying exponential functions with respective time-constants of 4 and 50 weeks [Eggermont, J.J., Salamy, A., 1988a. Maturational time-course for the ABR in preterm and full term infants. Hear Res 33, 35-47; Eggermont, J.J., Salamy, A., 1988b. Development of ABR parameters in a preterm and a term born population. Ear Hear 9, 283-9]. Here, we investigated the maturation of electrically evoked auditory brainstem responses (EABR) in 55 deaf children who recovered hearing after cochlear implantation, and proposed a predictive model of EABR maturation depending on the onset of deafness. The pattern of EABR maturation over the first 2 years of cochlear implant use was compared with the normal pattern of ABR maturation in hearing children.

METHODS

Changes in EABR wave V latency over the 2 years following cochlear implant connection were analyzed in two groups of children. The first group (n=41) consisted of children with early-onset of deafness (mostly congenital), and the second (n=14) of children who had become profoundly deaf after 1 year of age. The modeling of changes in EABR wave V latency with time was based on the mean values from each of the two groups, allowing comparison of the rates of EABR maturation between groups. Differences between EABRs elicited at the basal and apical ends of the implant electrode array were also tested.

RESULTS

There was no influence of age at implantation on the rate of wave V latency change. The main factor for EABR changes was the time in sound. Indeed, significant maturation was observed over the first 2 years of implant use only in the group with early-onset deafness. In this group maturation of wave V progressed as in the ABR model of [Eggermont, J.J., Salamy, A., 1988a. Maturational time-course for the ABR in preterm and full term infants. Hear Res 33, 35-47; Eggermont, J.J., Salamy, A., 1988b. Development of ABR parameters in a preterm and a term born population. Ear Hear 9, 283-9] of normal hearing children: a sum of two decaying exponential functions, one showing an early rapid decrease in latency and the other a slower decrease. Remarkably, the time-constants fell well within the ranges described by Eggermont and Salamy (i.e., 3.9 and 68 weeks), consistent with the time-course of the neurophysiological mechanisms presumably involved in auditory pathway maturation during the first 2 years of life: i.e., myelination and increased synaptic efficacy. In contrast, relatively little change in wave V was evident in children with late-onset deafness. In agreement with the notion that EABR maturation follows an apex-to-base gradient as described for ABR, we observed that wave V latencies were longer for the basal than the apical end of the implant electrode array and remained so throughout the study period, whatever the time of onset of deafness.

CONCLUSIONS

The findings in the early-onset of deafness group support the theory that auditory pathways remain "frozen" during the period of sensory deprivation until cochlear implant rehabilitation restores the normal chronology of maturational processes. In children with late-onset deafness, however, some maturational processes may occur before the onset of deafness, and thus less additional maturation is required during the first two years of implant use resulting in no significant EABR latency changes being observed in this period. The results suggest that the rehabilitation-induced plasticity of the auditory pathways is, in case of late auditory deprivation, unlikely to result in neurophysiological outcomes similar to those observed in children with early auditory deprivation.

SIGNIFICANCE

Changes in EABR wave V latency over the first 2 years of cochlear implant use were found to be well fitted by the sum of two decaying exponential functions in children with early-onset deafness. This is in line with the maturation of ABR wave V latency in normal-hearing children over the first two years of life. Further studies are needed to assess whether the differences observed in terms of auditory pathways maturation are associated with consistent differences in terms of language development.

A longitudinal study of electrical stimulation levels and electrode impedance in children using the Clarion cochlear implant

CONCLUSIONS

Electrical stimulation levels and electrode impedance values (EIVs) in children using the Clarion cochlear implant (CI) programmed with CIS strategy stabilized after 3 months of implant use. The data presented here may be useful as a general guideline for the programming of infants and young children and may further be of help for the identification of patients who fall outside the "average" range.

OBJECTIVES

The purpose of the present study was to evaluate changes in electrical stimulation levels, i.e. threshold (T) levels, comfortable (M) levels, dynamic range (DR), and EIVs during the first 18 months of implant use, in children using the Clarion CI.

MATERIALS AND METHODS

The maps of 18 pre-lingual children (mean age at implantation 4.2 years; range 1-8), using the Enhanced Bipolar 1.2 or Bipolar standard electrode with the S-Series speech processor programmed with CIS strategy, were examined at five time points: connection, and 3, 6, 12, and 18 months post-initial stimulation. T levels, M levels, DR and EIVs were analyzed according to four cochlear segments: apical, apical-medial, medial-basal, and basal.

RESULTS

During the first 3 months of implant use T levels increased to some extent, whereas M levels and DR increased significantly. From 3 months and through the entire follow-up, T and M levels as well as DR were stable. EIVs of current carrying electrodes decreased significantly from connection to the 3-month visit; thereafter a stabilization of values was evident. Electrical stimulation levels and EIVs did not differ among the cochlear segments during the entire follow-up.

Electrical stimulation levels and electrode impedance values in children using the Med-El Combi 40+ cochlear implant: a one year follow-up

The present study was designed to follow changes in electrical stimulation levels and electrode impedance values (EIV) in children using the Med-El Combi 40+ cochlear implant (CI) during the first 12 months of implant use. The maps of 24 prelingually deaf children implanted at a mean age of 5.9 years (range 1-15.9 years) using the TEMPO+ speech processor programmed with CIS+ strategy were examined at five time points: initial stimulation, and 1, 3, 6, and 12 months post-initial stimulation. Most comfortable levels (M) and electrode impedance values (EIV) were analyzed according to three cochlear segments: apical, medial, and basal. Results indicated a significant increase in M levels until the 3-month time point, thereafter stabilization was evident. Furthermore, M levels in the apical segment were lower than those in the medial and basal segments. EIV decreased from initial stimulation to the 3-month time point and was then stable through the study follow up. Interestingly, the finding of higher EIV in the apical segment may be attributed to the physical characteristics of the Med-El electrode. In conclusion, the pattern of stabilization of M levels found in the present study is similar to that reported for children using other devices. The data presented here may be useful as a guideline for programming M levels and monitoring EIV in infants and young children. They may further help clinicians to identify those children that fall outside the 'typical' range.