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Intra-operative recordings of electrically evoked auditory nerve action potentials in young children by use of neural response telemetry with the Nucleus CI24M cochlear implant
Abstract
The electrically evoked action potential (EAP) was recorded intra-operatively by use of neural response telemetry (NRT) on the Nucleus C124M cochlear implant. The aim of the present study was to investigate the EAP in young children immediately following implant surgery and whilst the children were still anaesthetized. The effect of data collection parameters on the reliability of the EAP was assessed and the relationships of the EAP findings to the intra-operative electrical auditory brainstem response (EABR) and early behavioural threshold levels (T-levels) were also investigated. The study data comprised intra-operative recordings in 60 children. Age at implantation was less than five years in 42 (70%) of the children. Aetiology of deafness was congenital in the majority of children (55, 92%), meningitic in four children and of unknown origin in one child. Optimum test parameters for the intra-operative EAP were an amplifier gain of 40 dB and a delay of 50 micros in order to minimize the effects of amplifier saturation due to stimulus artefact and to maximize the identification of the N1 component. An intra-operative protocol was established which involved recording four stimulus levels on each of the 22 electrodes of the electrode array, the range of stimulus levels being tailored towards the expected EAP thresholds and T-levels so as to identify response threshold. There was significant correlation between the intraoperative EAP thresholds and the early T-levels (Pearson's r = 0.93 ;p<0.01) when a correction factor was introduced based on a reliable behavioural measure of the threshold of electrical stimulation on electrode 10. The intra-operative EAP threshold, when combined with a limited amount of behavioural data, may therefore be used to predict the T-level with a useful degree of accuracy. This result is also supported by the significant correlation observed between the intra-operative thresholds of the EAP and EABR.
... The so-called 'reverse telemetry techniques' used enable the stimulation by biphasic electrical pulses of any electrode within the intracochlear array and the recording of the resulting eCAP from a neighbouring electrode. This eCAP measurement allows a verification of neuronal responsiveness to electrical stimulation and provides quantified objective information about actual auditory nerve functions [Brown et al., 1998;Mason et al., 2001]. In order to use eCAP thresholds for speech processor fitting, the correlation between those and behavioral levels have been studied in adults and children [Thai-Van et al., 2001;Franck and Norton, 2001;Dillier et al., 2002;Di Nardo et al., 2003;Kaplan-Neeman et al., 2004]. ...
... In order to use eCAP thresholds for speech processor fitting, the correlation between those and behavioral levels have been studied in adults and children [Thai-Van et al., 2001;Franck and Norton, 2001;Dillier et al., 2002;Di Nardo et al., 2003;Kaplan-Neeman et al., 2004]. Some investigators described a significant correlation when pooling several electrodes [Brown et al., 2000;Mason et al., 2001;Franck, 2002]. A small number of studies were aimed at determining speech perception following eCAP-based speech processor fitting [Franck, 2002;Seyle and Brown, 2002;Kaplan-Neeman et al., 2004]. ...
A sufficient correlation between objective (e.g. eCAP of the auditory nerve) and psychoacoustic data has not yet been possible due to high interindividual variability in cochlear implantees. Therefore, the application of objective data in the evaluation of speech rehabilitation after cochlear implantation was investigated. eCaps of all electrodes were measured intraoperatively. The 'threshold' and 'comfort' levels, speech recognition and pure tone thresholds were determined at follow-up. The correlation coefficient was calculated between eCap thresholds and psychoacoustic levels. This correlation coefficient was ranked with other individual items in relation to their influence on the development of speech recognition. Only the duration of preimplant deafness, the pure tone hearing threshold and the correlation between eCAP and psychoacoustic levels have a significant influence on the rehabilitation within this selection of variables. Based on these results, an individualized mathematical modeling approach was introduced to predict the development of postoperative speech recognition by incorporating objective data.
... Ces résultats ont mené au développement d'algorithmes ou de méthodes de programmation des IC à partir des ECAP (Botros and Psarros, 2010b;Gordon et al., 2002;Hughes et al., 2000;Mason et al., 2001), cependant ces techniques tendent à être moins efficientes que la programmation d'après les indications subjectives (Seyle and Brown, 2002) et ne sont utilisées que par défaut. ...
Cette thèse porte sur l'étude des liens entre des mesures électro-physiologiques du système auditif de la cochlée au tronc cérébral, les réglages et les performances auditives d'adultes utilisateurs d'implants cochleaires (IC) MED-EL ®.La majeure partie des travaux s'est intéressée aux ECAP (Electrically-evoked compound action potentials) traduisant l'activité synchrone des neurones auditifs cochléaires en réponse à la stimulation délivrée par l'IC. Ceux-ci ont été enregistrés soit lors de l'implantation, soit chez des utilisateurs expérimentés afin d'évaluer leur intérêt comme prédicteurs des niveaux de perceptions. Nos travaux montrent que malgré de grandes variations interindividuelles, les ECAP sont liés aux niveaux de perception. Cette relation ne permet cependant pas encore une prédiction suffisamment précise des niveaux de perception implémentés dans les réglages. Les IC MED-EL ® présentent la particularité de présenter les données d'impédance brutes sous forme de matrice de voltage pouvant servir à estimer la diffusion du courant autour de chaque électrode, au niveau de l'interface bioélectrique. Une partie des travaux a cherché à évaluer les relations entre diffusion du courant et compréhension de la parole. Les résultats indiquent que la compréhension de la parole ne semble pas liée à cette mesure de diffusion du courant intra-cochléaire.La dernière partie de cette thèse a évalué les relations entre une mesure électro-physiologique de l'intégration binaurale (BIC pour Binaural Interaction Component) et performances binaurales chez des sujets dont l'audition est entièrement médiée par l'IC. Cette étude suggère que les sujets présentant des BIC identifiables semblent tirer un meilleur profit de la binauralité
... Les premiers enregistrements de potentiels évoqués auditifs directs sur le nerf sont dus à Wever et Bray [Wever 1930], et les premières applications en bloc opératoire sont dues à [Moller 1981a]. La technique consiste à enregistrer des potentiels électriques de champ proche, à proximité du champ opératoire, soit par EcochG, soit par potentiel direct sur le VIII [Battista 2000;Mason 2001;Moller 1983;Palm 2001;Rosahl 2000;Sabin 1987;Sekiya 1983], soit enfin par enregistrement au niveau du noyau cochléaire par insertion profonde de l'électrode dans le récessus latéral du IV ème ventricule [Moller 1994b] (figure VI-1). Le but du monitorage auditif par cette méthode est la détection précoce de modifications du potentiel d'action composite qui serait le reflet fiable d'une détérioration auditive en cours [Colletti 1998b;Nadol 1987;Silverstein 1985a]. ...
Intra-operative auditory monitoring using auditory brainstem responses (ABR) is rapidly evolving as an important adjunct during surgery in the cerebello-pontine angle to reduce the incidence of auditory deficits. Auditory monitoring alerts the surgeon to ongoing changes in neural function, but the existing techniques have their limitations, suggesting the application of new methods. A specific compact equipment was designed for this purpose. It enables to provide near real time information (within 10 sec) on the ongoing auditory status. The dedicated software includes a dedicated rejection algorithm and an FFT analysis. Recordings have been performed in 23 patients. This study suggests that our technique had significant technical benefits in comparison with other methods of monitoring, although the differences in hearing preservation rates are not statistically significant. To improve the efficacy of intraoperative auditory monitoring auditory direct eight nerve monitoring (DENM) will be combined with auditory brainstem response (ABR). To achieve this goal, a multipoint flexible surface microelectrode for direct cortical recordings with a high spatiotemporal resolution has been fabricated and tested in animals. Recordings of cortical activities elicited by both acoustic and electrical stimulation on the cochlear nucleus have focused on the feasibility. Such electrodes are expected to enhance auditory neural coding understanding and provide new developments in human auditory monitoring.
... When a sufficient number of electrodes are tested for neural responses in the operating room, the results yield a contour that helps to predict the contour of the comfort levels of the map at activation of the device (Mason, Cope, Garnham, O'Donoghue, & Gibbin, 2001). Because the current levels required to measure the neural response are perceptually loud for a new user, these intraoperative measures are particularly valuable to have when activating a young child's implant. ...
... These have encouraged the increasingly widespread use of TNRT profiles in assisting with speech processor programming, especially for very young children (e.g. Hughes et al. 2000, Mason et al. 2001, Gordon et al. 2002, Kaplan-Neeman et al. 2004) as well as the elderly (e.g. Pedley et al. 2007). ...
This study investigates the effect of the Nucleus CI24RE implant's neural response telemetry (NRT) system, which has less internal noise compared to its predecessor, the CI24M/R implant, on the NRT threshold (TNRT) profile across the array. CI24M/R measurements were simulated by ignoring CI24RE measurements with response amplitudes below 50 uV. Comparisons of the estimated TNRTs from the CI24RE measurements and the CI24M/R simulations suggest that, apart from a constant level difference, the TNRT profiles from the newer implant generally would not have differed very much from those of its predecessor. This view was also reflected by principal component analysis (PCA) results which revealed a 'shift' component similar to that reported by Smoorenburg et al (2002). On the whole, there is no indication that current practices of using the TNRT profiles for assisting with speech processor programming need to be revised for the CI24RE implant.
... Programming sessions were performed at initial stimulation, and then at 1, 3, 6, and 12 months. T and C levels were analyzed at three different cochlear segments: basal (electrodes 1-7), medial (electrodes [8][9][10][11][12][13][14], and apical (electrodes [15][16][17][18][19][20][21][22]. ...
The present study was designed to evaluate the effect of neural response telemetry (NRT)-based cochlear implant (CI) programming versus behavioral-based programming on electrical stimulation parameters (MAP) threshold (T) and comfortable (C) levels and speech perception abilities in young children, during the first year of implant use. Ten congenitally deaf children at the age of 12-39 months (mean age: 25.2 months) implanted with the Nucleus 24R(CS) CI participated in the study. The group was randomly divided into two: (1) NRT-based MAP group (n = 5) consisted of children who were programmed using intra-operative NRT measurements; (2) behavioral-based MAP group (n = 5) consisted of children who were programmed using the behavioral responses of the patients. MAP parameters as well as sound-field aided thresholds and speech perception abilities were compared between the two groups at consecutive programming sessions: 1, 3, 6, and 12 months post initial stimulation. Results indicated no significant differences among NRT-based MAPs and behavioral-based MAPs. Although MAP profiles at initial stimulation differed in the apical region, these differences decreased with time. In addition, a gradual increase of T and C levels of NRT-based MAPs as well as those of behavioral-based MAPs was evident until the 1-month time point, thereafter stabilization occurred. Sound-field aided thresholds improved with time for both groups; however, they were found to be significantly better for the NRT-based MAP group. Despite these differences, speech perception abilities were comparable among groups at 12 months post initial stimulation. NRT-based programming was found to be significantly shorter than behavioral-based programming. In conclusion, for this small group of children, our findings support the use of NRT for programming of young children during the initial period after implantation.
... To improve the correlation, several studies have attempted to reduce the individual differences by shifting the eCAP thresholds across electrodes so that the eCAP threshold on one anchor electrode is equal to the T or MCL levels for the same electrode measured at a high stimulus rate using the conventional fitting procedure. 9,[19][20][21][22] The anchor electrode is normally in the middle of the array. Without shifting individual eCAP threshold profiles, Brown and colleagues 9 found correlations of 0.55 and 0.56 across subjects between eCAP thresholds and the T and MCL level, respectively. ...
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.
Intraoperative assessment of electrode function and position is essential for cochlear implant outcomes. Electrophysiological measures and radiographic imaging modalities have been used for this purpose. This study was conducted to determine the relative utility of X-ray, impedance measurements and ECAP for cochlear implant function.
A retrospective review was conducted for 132 children (age range from 5 to 13 years old) who underwent cochlear implantation. 3 months after switch on, aided free field (FF) and Ling Six Sounds were compared between patients who had intraoperative ECAP and those who had not intraoperative ECAP (but with normally located electrode array as confirmed by plain X-ray).
Only 4 cases (3%) had abnormal impedance measurements that became normal after reinsertion of the same electrode array. 3 cases (2.3%) showed malposition of the electrode array on plain radiograph. They underwent immediate revision. 11 cases (8.3%) had absent intraoperative ECAP response for all electrodes, and 4 cases (3%) had absent intraoperative ECAP response for basal electrodes. These devices were not explanted at the time of surgery. 3 months after switch on, FF and the ling 6 sounds were tested for all patients. No statistical significant differences were found between cases with normal intraoperative ECAP and those who gave no response in ECAP.
From the study we can conclude that plain X-ray is the guideline for backup use. Results of plain X-ray impacted surgical decision making and led to the use of the backup device. In patients with correct electrode placement in normally developed cochlea as detected by X-ray, it is not recommended to use the backup even if there is no intraoperative ECAP. Also, it is recommended to follow how those children performed after 1 or 2 years to see if making the decision of using or not a backup device based in electrophysiology measures vs X-ray made a difference.
Copyright © 2015 Elsevier Ireland Ltd. All rights reserved.
The cochlear implant is the most successful neural prosthesis developed to date. Approximately 60,000 people have received cochlear implants as of this writing. This number exceeds by orders of magnitude the numbers for any other type of neural prosthesis. According to the recent National Institutes of Health (NIH) Consensus Statement on Cochlear Implants (1995), “A majority of those individuals with the latest speech processors for their implants will score above 80 percent correct on high-context sentences, even without visual cues.” This level of success is truly remarkable, given the relatively crude representations of speech and other sounds provided by present implant systems.
Neuropathology around the cochlea could create variation from site to site in physiological thresholds of cochlear implant users. This variability would be detrimental to speech recognition with a cochlear implant for a variety of reasons, including distortion of the place code and variation in the number of neurons. The purpose of this study is to examine the relationship between thresholds of electrically evoked compound action potential (ECAP) and speech perception in children implanted with the Nucleus Freedom devices.
Intraoperative testing of cochlear implant devices, establishment of electrical threshold for acoustic reflex, and recording neural responses to electrical stimulation have traditionally required the presence of a cochlear implant audiologist in the operating room. The goal of this study was to determine the feasibility of remote testing to improve time efficiency and reduce cost.
Prospective.
A standard PC with Tridia VNC software and either Cochlear Corporation or Advanced Bionics Corporation mapping software was configured to perform remote testing. The time required to perform on-site or remote testing was measured.
With the availability of the laptop and internet access, there were no geographic restrictions regarding the site of remote testing. Remote testing was time efficient, requiring 9 minutes of audiologist's time compared with 93 minutes when the audiologist had to travel to the operating room.
Remote testing of the cochlear implant device and patient's response to electrical stimulation is technically feasible. It is timesaving, practical, and cost efficient.
To investigate postoperative outcomes after cochlear implantation in young children with cochlear nerve deficiency and compare the results with those of cochlear implantation in patients with normal cochlear nerve.
Historical cohort study.
Tertiary referral center.
Six children under the age of 36 months with cochlear nerve deficiency, as determined by magnetic resonance imaging (MRI), received cochlear implantation between July 2006 and March 2008. Fifteen children under the age of 36 months with normal cochlear nerve in the implanted ear underwent cochlear implantation during the same period and were selected as the control group. Medical records, imaging studies, and speech evaluations were reviewed.
Our study group scored lower in the Infant-Toddler Meaningful Auditory Integration Scale compared to the control group. Our study group produced categories of auditory performance scores not less than 4 except for one patient. Speech intelligibility rating scores in the control group gradually increased after cochlear implantation, but for the study group, the score remained zero 12 months after the implantation. In open-set one-syllable tests, five patients with cochlear nerve deficiency showed no response at the latest follow-up, whereas patient 6 began to show delayed improvement after 18 months. The results of the open-set two-syllable test were similar to those of the open-set one-syllable test.
Young children with nonvisualized cochlear nerve on MRI showed worse outcomes compared to the children with normal cochlear nerve. Cochlear nerve deficiency on MRI is a marker of very poor outcome with cochlear implantations.
The purpose of this review is to summarize current thinking relative to clinical applications for the electrically evoked compound action potential and the electrically evoked auditory brainstem response with the focus on works published between 1998 and 2003.
During the period of this review, a considerable body of research has been published describing how the electrically evoked compound action potential can be measured and how the electrically evoked compound action potential may be used in the clinical treatment of cochlear implant patients. During this same period, there has been a decline in the number of studies reporting potential clinical applications for the electrically evoked auditory brainstem response. Perhaps the strongest clinical application for the electrically evoked compound action potential today is as a tool to facilitate the process of fitting the speech processor of the cochlear implant. This is particularly important for pediatric patients who may not be able to be programmed using traditional behavioral techniques. The accuracy of these predictions is discussed in addition to the limitations of the studies reviewed.
The introduction of cochlear implants with the capability of measuring the response of the auditory nerve to electrical stimulation from an intracochlear electrode has tremendous potential to impact clinical practice. Research into how best to use this information is ongoing.
The auditory nerve's electrically evoked compound action potential is recorded in deaf patients equipped with the Nucleus 24 cochlear implant using a reverse telemetry system (NRT). Since the threshold of the NRT response (NRT-T) is thought to reflect the psychophysics needed for programming cochlear implants, efforts have been made by specialized management teams to develop its use. This study aimed at developing a valid tool, based on artificial neural networks (ANN) technology, for automatic estimation of NRT-T. The ANN used was a single layer perceptron, trained with 120 NRT traces. Learning traces differed from data used for the validation. A total of 550 NRT traces from 11 cochlear implant subjects were analyzed separately by the system and by a group of physicians with expertise in NRT analysis. Both worked to determine 37 NRT-T values, using the response amplitude growth function (AGF) (linear regression of response amplitudes obtained at decreasing stimulus intensity levels). The validity of the system was assessed by comparing the NRT-T values automatically determined by the system with those determined by the physicians. A strong correlation was found between automatic and physician-obtained NRT-T values (Pearson r correlation coefficient >0.9). ANOVA statistics confirmed that automatic NRT-Ts did not differ from physician-obtained values (F = 0.08999, P = 0.03). Moreover, the average error between NRT-Ts predicted by the system and NRT-Ts measured by the physicians (3.6 stimulation units) did not differ significantly from the average error between NRT-Ts measured by each of the three physicians (4.2 stimulation units). In conclusion, the automatic system developed in this study was found to be as efficient as human experts for fitting the amplitude growth function and estimating NRT-T, with the advantage of considerable time-saving.
Objective:
In cochlear implant recipients, the threshold of the electrically evoked compound action potential (ECAP) has been shown to correlate with the perceptual detection threshold and maximum comfortable loudness levels (respectively, T- and C-levels) used for implant programming. Our general objective was to model the relationship between ECAP threshold and T/C-levels by taking into account their relative changes within each subject. In particular, we were interested in investigating further the validity of ECAP threshold as a predictor of psychophysical levels, depending on intra-cochlear electrode location and time of testing (from 1 to 18 months post-implantation).
Methods:
A total of 370 ECAP thresholds, measured in 49 children, using a Nucleus 24 cochlear implant, were compared with the corresponding T- and C-levels obtained at the same visit, for the same electrode. Response profiles for the whole group of patients were modeled across four test electrodes spaced equally along the electrode array from base towards apex. A linear regression model was constructed and the quality of the ECAP threshold-based predictions was assessed by testing for correlation between measured and predicted psychophysics. Comparison was made with a more simplistic model (described here as the 'parallel profiles method') stipulating, within each subject, a 1 microA increase in psychophysical levels for every 1 microA increase in ECAP threshold.
Results:
Offset between ECAP threshold and psychophysics profiles was found to vary significantly along the electrode array for the T-, but not for the C-level. In contrast with the parallel profiles method, our regression model predicted, within each subject, an average increase of 0.23 microA (95% confidence interval: 0.18-0.28) in T-level for every 1 microA increase in ECAP threshold. This correction improved the quality of T-level prediction when our model was run using measured T-level and ECAP threshold from a reference electrode (r=0.77 vs. r=0.62). The shorter the distance between the electrode for which T-level was predicted and the one used as reference, the stronger the correlation between measured and predicted T-levels. In addition, poorer T-level predictions were obtained at the basal end of the array during the first 3 months post-implantation. In contrast to T-level, individual changes in C-level with ECAP threshold exhibited heterogeneous patterns across subjects so that no common coefficient could account for these changes. However, applying the parallel profiles method led to high-quality C-level prediction.
Conclusions and significance:
The results suggest that covariation between ECAP thresholds and psychophysics plays a decisive role in the relationship of ECAP threshold with T-, but not with C-level. Therefore, our regression model and the parallel profiles method should both be used for predicting, respectively, the T- and the C-levels. Although the predictability of our regression model seems to be better for middle and apical electrodes, its utilization should be extended to basal electrodes after 6 months' implant use.
One hundred and forty-seven adult recipients of the Nucleus 24 cochlear implant system, from 13 different European countries, were tested using neural response telemetry to measure the electrically evoked compound action potential (ECAP), according to a standardised postoperative measurement procedure. Recordings were obtained in 96% of these subjects with this standardised procedure. The group results are presented in terms of peak amplitude and latency, slope of the amplitude growth function and ECAP threshold. The effects of aetiological factors and the duration of deafness on the ECAP were also studied. While large intersubject variability and intrasubject variability (across electrodes) were found, results fell within a consistent pattern and a normative range of peak amplitudes and latencies was established. The aetiological factors had little effect on the ECAP characteristics. However, age affected ECAP amplitude and slope of the amplitude growth function significantly; i.e., the amplitude is higher in the lowest age category (15-30 years). Principal component analysis of the ECAP thresholds shows that the thresholds across 5 electrodes can be described by two factors accounting for 92% of the total variance. The two factors represent the overall level of the threshold profiles ('shift') and their slopes across the electrode array ('tilt'). Correlation between these two factors and the same factors describing the T- and C-levels appeared to be moderate, in the range of 0.5-0.6.
Electrophysiologic and objective measures are reviewed with respect to their implementation as monitoring tools for cochlear implants in the operating room and their value in the management of children. The current intraoperative test protocol in Nottingham consists of back-telemetry (BT) diagnostic testing of implant function, including impedance telemetry (ImpT), integrity testing (IT), electrical stapedius reflex response (ESR), electrical auditory brainstem response (EABR) and Neural Response Telemetry (NRT). Of 427 cases of implantation in the period 1990-2003, 303 (71%) were completely normal for all components of the protocol. In the remaining cases, some results were either simply anomalous, with no direct impact on management during surgery, and some were more significant, resulting in actions such as the use of the back-up device or repositioning of the electrode array. Normal intraoperative findings provided immediate reassurance to the implant team and parents of young children that the implant was fully functioning and that electrical stimulation was activating the auditory pathways These objective measures also identified potentially challenging cases, such as those with low levels of sensitivity to electrical stimulation and susceptibility to facial nerve stimulation. An audit showed that intraoperative measures provided valuable assistance in the initial fitting of the device.
The purpose of this study was to evaluate the performance of the new features of the Nucleus Research Platform 8 (RP8), a system developed specifically for research purposes The RP8 consists of a research implant, a speech processor and a new NRT software (NRT v4), and includes comparisons of the different artefact-cancellation methods, NRT threshold, and recovery function measurements. The system has new artefact-suppression techniques and new diagnostic capabilities; their performance has been verified in animal experiments. In this study, NRT data were collected from 15 postlingually deafened adult cochlear implant patients intraoperatively and up to 6 months postoperatively after switch-on. The initial investigation in two clinics in Europe focused primarily on the enhanced NRT capabilities Results from the trial in two European clinics indicate that NRT measurements can be obtained with lower noise levels. A comparison of the different artefact-cancellation techniques showed that the forward-masking paradigm implemented in the Nucleus 3 system is still the method of choice. The focus of this report is on recovery function characteristics, which may give insight into auditory nerve fiber properties with regard to higher stimulation rates.
The objective of the study was to investigate the potential for clinical application of neural response imaging (NRI) cochlear mapping. Cochlear mapping was performed at each fitting session up to at least six months following initial fitting. Stimulation was delivered to one electrode site. NRI was recorded from each of the remaining sites. The procedure was repeated for apical, medial and basal stimulation sites, stimulating at subjective threshold and most comfortable levels. Responses were obtained in five out of six subjects and are discussed in terms of: reproducibility, quality, changes over time. Cochlear mapping provided repeatable data that gave interesting insights into the implanted cochlea. Further work is required to determine whether this approach could contribute to programme optimisation.
To investigate the relationship between single-channel and banded neural response imaging (NRI) responses and to evaluate whether banded NRI measurements are better correlated to fitting parameters than single-channel NRI measurements.
Nineteen profoundly deaf subjects implanted with a HiRes 90K cochlear implant from Advanced Bionics Corporation (Valencia, CA).
Neural response imaging thresholds (tNRIs; single-channel and banded tNRIs) were measured intraoperatively; at first fitting; and after 3, 6, and 12 months of implant use. Relationships between those measurements and correlations between those measurements and implant program parameters were investigated.
Single-channel and banded tNRI collected at each measurement session.
Banded NRI could be recorded reliably and was not more time-consuming than the routine single-channel NRI. Significant correlations (Pearson R; p < 0.05) were observed between first-fitting banded tNRI and most comfortable levels at 12 months, with a higher level of significance than the correlations observed with single-channel tNRI.
Banded NRI may be a more appropriate fitting tool than single-channel NRI. However, the sample size was small, and more data are necessary to confirm these findings.
Thesis (Ph. D.)--University of Washington, 1999 The goal of this study was to explore the clinical utility of the electrically evoked whole-nerve action potential (EAP), measured with the Neural Response Telemetry (NRT) capabilities of Cochlear Corporation's Nucleus C124M cochlear implant system. Users of the C124M cochlear implant system followed at the University of Washington with at least three months of implant experience were subjects (n = 12) in this study. EAP growth and refractory recovery functions were successfully quantified on each active electrode of every subject. In addition, two measures of loudness growth were explored at 80 Hz (the frequency of the EAP stimuli) and at 250 Hz (the frequency of clinical implant fitting stimuli). The first loudness measure was a repeated ascending and descending method of adjustment using a continuous signal. The second loudness measure was a magnitude estimation technique. Other information including performance, etiology and duration of hearing loss, and individual electrode, impedance was considered. EAP thresholds were found to be highly correlated with threshold loudness responses. The rate of EAP growth with increasing stimulation levels was also found to be correlated with the dynamic range of loudness limits and threshold loudness responses. Inconsistencies were found between the two methods used to measure loudness growth. No relationship was evident between EAP measures and performance. EAP measures can be used to estimate loudness information used in cochlear implant fitting. Suggested cochlear implant fitting protocols based on EAP measures may be more reliable than protocols based only on loudness techniques.
This study describes a method for recording the electrically evoked, whole-nerve action potential (EAP) in users of the Ineraid cochlear implant. The method is an adaptation of one originally used by Charlet de Sauvage et al. [J. Acoust. Soc. Am. 73, 615-627 (1983)] in guinea pigs. The response, recorded from 11 subjects, consists of a single negative peak that occurs with a latency of approximately 0.4 ms. EAP input/output functions are steeply sloping and monotonic. Response amplitudes ranging up to 160 micro V have been recorded. Slope of the EAP input/output function correlates modestly (approximately 0.6-0.69) with results of tests measuring word recognition skills. The refractory properties of the auditory nerve were also assessed. Differences across subjects were found in the rate of recovery from the refractory state. These findings imply that there may be difference across subjects in the accuracy with which rapid temporal cues can be coded at the level of the auditory nerve. Reasonably strong correlations (approximately 0.74-0.85) have been found between the magnitude of the slope of these recovery curves and performance on tests of word recognition.
A method for recording the electrically evoked whole-nerve action potential (EAP) at the time of cochlear implant surgery is described. Measures of EAP growth with stimulus level and functions describing the rate of recovery of the auditory nerve from the refractory state are reported for patients tested intraoperatively and for a group of patients using the ineraid implant, from whom recordings were made following implantation. Subjects tested intraoperatively were separated into three categories: congenitally deaf children (n = 14), prelingual meningitic children (n = 5), and postingual adults (n = 13). A fourth group consisted of postlingual adults (n = 14) tested postoperatively. Results from all groups showed a similar range of EAP growth and recovery rates across patients. Data from congenitally deaf children formed the exception showing steeper EAP growth functions than other subject groups. Electrically evoked whole-nerve action potential growth and recovery functions of the postoperative group of subjects showed modest correlations to speech perception scores measured after at least 18 months of implant use. The possible use of these measures in fitting an implant to an individual is discussed.
This study outlines a series of experiments using the neural response telemetry (NRT) system of the Nucleus CI24M cochlear implant to measure the electrically evoked compound action potential (EAP). The goal of this investigation was to develop a protocol that allows successful recording of the EAP in a majority of CI24M cochlear implant users.
Twenty-six postlingually deafened adults participated in this study. A series of experiments were conducted that allowed us to examine how manipulation of stimulation and recording parameters may affect the morphology of the EAP recorded using the Nucleus NRT system.
Results of this study show consistent responses on at least some electrodes from all subjects. Cross-subject and cross electrode variations in both the growth of the response and the temporal refractory properties of the response were observed. The range of stimulus and recording parameters that can be used to record the EAP with the Nucleus NRT system is described.
Using the protocol outlined in this study, it is possible to reliably record EAP responses from most subjects and for most electrodes in Nucleus CI24M cochlear implant users. These responses are robust and recording these responses does not require that the subject sleep or remain still. Based on these results, a specific protocol is proposed for measurement of the EAP using the NRT system of the CI24M cochlear implant. Potential clinical implications of these results are discussed.
The purpose of this study is to examine the relationship between the electrically evoked compound action potential (EAP) thresholds and the MAP thresholds (T-levels) and maximum comfort levels (C-levels) in children implanted with the Nucleus 24 device.
EAP thresholds were measured using the Neural Response Telemetry system of the Nucleus 24 device. Twenty children implanted with the Nucleus 24 cochlear implant participated in this study. EAP thresholds were compared with the behavioral measures of T- and C-level used to construct the MAP these children used on a daily basis. For these subjects, both EAP and MAP T- and C-levels were obtained the same visit, which occurred at 3 to 5 mo postconnection.
EAP thresholds were shown to fall between MAP T- and C-level for 18 of 20 subjects tested; however, considerable variability across subjects was noted. On average, EAP thresholds fell at 53% of the MAP dynamic range. Correlations between EAP threshold and MAP T- and C-level improved substantially when combined with behavioral measures obtained from one electrode in the array.
Moderate correlations were found between EAP thresholds and MAP T- and C-levels for the children participating in this study. However, a technique is described for improving the accuracy of predictions of MAP T- and C-levels based on EAP data combined with a small amount of behavioral information.
The objective of this study was to determine the relationship between electrically evoked whole nerve action potential (EAP) and electrical auditory brain stem response (EABR) thresholds and MAP threshold (T-level) and maximum comfort level (C-level) for subjects who use the Nucleus 24 cochlear implant system.
Forty-four adult Nucleus 24 cochlear implant users participated in this study. EAP thresholds were recorded using the Neural Response Telemetry System developed by Cochlear Corporation. EABR thresholds were measured for a subset of 14 subjects using standard evoked potential techniques. These physiologic thresholds were collected on a set of five electrodes spaced across the cochlea, and were then compared with behavioral measures of T-level and C-level used to program the speech processor.
EAP thresholds were correlated with MAP T- and C-levels; however, the correlation was not strong. A technique for improving the correlation by combining measures of T- and C-levels made on one electrode with the EAP thresholds was presented. Correlations between predicted and measured T- and C-levels using this technique were 0.83 and 0.77, respectively. Similar results were obtained using the EABR thresholds for a smaller set of subjects. In general, EABR thresholds were recorded at levels that were approximately 4.7 programming units lower than EAP thresholds.
Either EAP or EABR thresholds can be used in combination with a limited amount of behavioral information to predict MAP T- and C-levels with reasonable accuracy.
This paper describes the neural response telemetry (NRT) results obtained from the first 30 patients tested at this centre. One hundred per cent of patients tested intra-operatively had NRT responses on at least one electrode; this compared to 82.4% of patients tested post-operatively. Reasonable correlations existed between post-operative NRT thresholds and psychophysical threshold and comfort levels, although there was too much variability for the data to be used to set these parameters directly. Post-operative NRT thresholds were always at levels audible to patients.
Behavioural hearing tests six months to 3;6 years
- B Mccormick
Fitting and programming the external system
- Y Cope
- C Totten
Fitting and programming the external system
- S Sheppard
Current Clinical Application of NRT in Europe: Survey of Results. Presented at the 8th NRT Research Workshop
- D Cafarelli-Dees