eCAP Thresholds Research Articles

Prediction of the Functional Status of the Cochlear Nerve in Individual Cochlear Implant Users Using Machine Learning and Electrophysiological Measures.

This study aimed to create an objective predictive model for assessing the functional status of the cochlear nerve (CN) in individual cochlear implant (CI) users. Study participants included 23 children with cochlear nerve deficiency (CND), 29 children with normal-sized CNs (NSCNs), and 20 adults with various etiologies of hearing loss. Eight participants were bilateral CI users and were tested in both ears. As a result, a total of 80 ears were tested in this study. All participants used Cochlear Nucleus CIs in their test ears. For each participant, the CN refractory recovery function and input/output (I/O) function were measured using electrophysiological measures of the electrically evoked compound action potential (eCAP) at three electrode sites across the electrode array. Refractory recovery time constants were estimated using statistical modeling with an exponential decay function. Slopes of I/O functions were estimated using linear regression. The eCAP parameters used as input variables in the predictive model were absolute refractory recovery time estimated based on the refractory recovery function, eCAP threshold, slope of the eCAP I/O function, and negative-peak (i.e., N1) latency. The output variable of the predictive model was CN index, an indicator for the functional status of the CN. Predictive models were created by performing linear regression, support vector machine regression, and logistic regression with eCAP parameters from children with CND and the children with NSCNs. One-way analysis of variance with post hoc analysis with Tukey's honest significant difference criterion was used to compare study variables among study groups. All three machine learning algorithms created two distinct distributions of CN indices for children with CND and children with NSCNs. Variations in CN index when calculated using different machine learning techniques were observed for adult CI users. Regardless of these variations, CN indices calculated using all three techniques in adult CI users were significantly correlated with Consonant-Nucleus-Consonant word and AzBio sentence scores measured in quiet. The five oldest CI users had smaller CN indices than the five youngest CI users in this study. The functional status of the CN for individual CI users was estimated by our newly developed analytical models. Model predictions of CN function for individual adult CI users were positively and significantly correlated with speech perception performance. The models presented in this study may be useful for understanding and/or predicting CI outcomes for individual patients.

The Effect of Interphase Gap on Neural Response of the Electrically Stimulated Cochlear Nerve in Children With Cochlear Nerve Deficiency and Children With Normal-Sized Cochlear Nerves.

This study aimed to compare the effects of increasing the interphase gap (IPG) on the neural response of the electrically stimulated cochlear nerve (CN) between children with CN deficiency (CND) and children with normal-sized CNs. Study participants included 30 children with CND and 30 children with normal-sized CNs. All subjects were implanted with a Cochlear Nucleus device with the internal electrode array 24RE[CA] in the test ear. The stimulus was a charge-balanced, cathodic leading, biphasic pulse with a pulse-phase duration of 50 μsec. For each subject, the electrically evoked compound action potential (eCAP) input/output (I/O) function was measured for 6 IPGs (i.e., 7, 14, 21, 28, 35, and 42 μsec) at 3 electrode locations across the electrode array. For each subject and each testing electrode, the highest stimulation used to measure the eCAP I/O function was the maximum comfortable level measured with an IPG of 42 μsec. Dependent variables (DVs) were the maximum eCAP amplitude, the eCAP threshold, and the slope of the eCAP I/O function estimated using both linear and sigmoidal regression functions. For each DV, the size of the IPG effect was defined as the proportional change relative to the result measured for the 7 μsec IPG at the basal electrode location. Generalized linear mixed effect models with subject group, electrode location, and IPG duration as the fixed effects and subject as the random effect were used to compare these DVs and the size of the IPG effect on these DVs. Children with CND showed smaller maximum eCAP amplitudes, higher eCAP thresholds, and smaller slopes of eCAP I/O function estimated using either linear or sigmoidal regression function than children with normal-sized CNs. Increasing the IPG duration resulted in larger maximum eCAP amplitudes, lower eCAP thresholds and larger slopes of eCAP I/O function estimated using sigmoidal regression function at all three electrode locations in both study groups. Compared with children with normal-sized CNs, children with CND showed larger IPG effects on both the maximum eCAP amplitude and the slope of the eCAP I/O function estimated using either linear or sigmoidal regression function, and a smaller IPG effect on the eCAP threshold than those measured in children with normal-sized CNs. Increasing the IPG increases responsiveness of the electrically stimulated CN in both children with CND and children with normal-sized CNs. The maximum eCAP amplitude and the slope of the eCAP I/O function measured in human listeners with poorer CN survival are more sensitive to changes in the IPG. In contrast, the eCAP threshold in listeners with poorer CN survival is less sensitive to increases in the IPG. Further studies are warranted to identify the best parameters of eCAP results for predicting CN survival before this eCAP testing paradigm can be used as a clinical tool for evaluating neural health for individual cochlear implant patients.

Relationship Between Speech Recognition in Quiet and Noise and Fitting Parameters, Impedances and ECAP Thresholds in Adult Cochlear Implant Users.

The objective of this study was to identify parameters which are related to speech recognition in quiet and in noise of cochlear implant (CI) users. These parameters may be important to improve current fitting practices. Adult CI users who visited the Amsterdam UMC, location VUmc, for their annual follow-up between January 2015 and December 2017 were retrospectively identified. After applying inclusion criteria, the final study population consisted of 138 postlingually deaf adult Cochlear CI users. Prediction models were built with speech recognition in quiet and in noise as the outcome measures, and aided sound field thresholds, and parameters related to fitting (i.e., T and C levels, dynamic range [DR]), evoked compound action potential thresholds and impedances as the independent variables. A total of 33 parameters were considered. Separate analyses were performed for postlingually deafened CI users with late onset (LO) and CI users with early onset (EO) of severe hearing impairment. Speech recognition in quiet was not significantly different between the LO and EO groups. Speech recognition in noise was better for the LO group compared with the EO group. For CI users in the LO group, mean aided thresholds, mean electrical DR, and measures to express the impedance profile across the electrode array were identified as predictors of speech recognition in quiet and in noise. For CI users in the EO group, the mean T level appeared to be a significant predictor in the models for speech recognition in quiet and in noise, such that CI users with elevated T levels had worse speech recognition in quiet and in noise. Significant parameters related to speech recognition in quiet and in noise were identified: aided thresholds, electrical DR, T levels, and impedance profiles. The results of this study are consistent with previous study findings and may guide audiologists in their fitting practices to improve the performance of CI users. The best performance was found for CI users with aided thresholds around the target level of 25 dB HL, and an electrical DR between 40 and 60 CL. However, adjustments of T and/or C levels to obtain aided thresholds around the target level and the preferred DR may not always be acceptable for individual CI users. Finally, clinicians should pay attention to profiles of impedances other than a flat profile with mild variations.

Electrode Translocations in Perimodiolar Cochlear Implant Electrodes: Audiological and Electrophysiological Outcome

IntroductionDespite using the soft-surgery technique, cochlear implantation may increase the damage of the intracochlear structures due to a scalar translocation of the electrode. The aim of this work was to investigate the incidence as well as the audiological and electrophysiological outcome for electrode translocations and complete scala tympani insertions of perimodiolar electrodes within a large group of patients. Material and methodsThe investigations were performed retrospectively on 255 adult subjects with a Nucleus Contour Advance or Slim Modiolar electrode (Cochlear Ltd.). The scalar position was assessed by postoperative rotational tomography. Intraoperative and one year after CI activation measured ECAP thresholds were examined as well as the postoperative speech recognition in quiet using the Freiburg monosyllable word test. ResultsThe incidence of a translocation was significantly lower with the Slim Modiolar than with the Contour Advance electrode (5.1% versus 32.3%; p<0.05). With a scala tympani placement the median speech recognition score was 75% (range: 20- 100%) with the Contour Advance and 72.5% (range: 27.5-95%) with the Slim Modiolar electrode. In cases with an electrode translocation, speech recognition scores show a median of 75% (range: 45-100%) and 73.8% (range: 40-80%), respectively. No significant differences in speech recognition were found between translocations and scala tympani insertions with both electrodes. Compared to scala tympani insertions, electrode translocations yielded higher ECAP thresholds at apical and medial electrode contacts (p<0.05). ConclusionThe incidence of an electrode translocation is determined for both perimodiolar electrode types analyzed in this work. ECAP measurements provide additional information for detecting translocations compared to radiological imaging. However, the postoperative speech recognition in quiet was not affected by the scalar position in the electrodes examined here.

The Effect of Aging on the Electrically Evoked Compound Action Potential.

To examine the effect of aging on electrically evoked compound action potential (eCAP) growth functions and their relationship with speech recognition in noise in cochlear implant (CI) users. Aging typically leads to difficulty understanding speech in background noise. Previous research has explored cognitive and central auditory mechanisms contributing to these age-related changes. However, it is likely that the peripheral auditory system may also play a role. One challenge is separating the effects of aging on cochlear structures from the effects of aging on the auditory nerve in humans. CI users provide a unique way to address this issue, as intracochlear electrical stimulation bypasses surviving hair cells and activates the auditory nerve directly. Studies in animal models suggest that age-related loss of spiral ganglion cells could lead to shallower eCAP growth functions and/or increased eCAP thresholds and potentially negatively impact speech recognition. Ten younger and 10 older postlingually deafened, adult CI recipients participated in this study. eCAP amplitude-intensity functions were recorded from a mid-array electrode and fit using linear functions. Speech recognition in noise was assessed using the Quick Speech-in-Noise (QuickSIN) test. Older CI users had significantly shallower eCAP growth functions and higher eCAP thresholds than younger CI users. eCAP growth functions were not correlated with speech recognition in noise. Results of this study suggest that older adults may have poorer neural survival, resulting in higher eCAP thresholds and shallower eCAP growth functions. These findings expand our understanding of mechanisms underlying age-related changes in the peripheral auditory system.

The Effects of GJB2 or SLC26A4 Gene Mutations on Neural Response of the Electrically Stimulated Auditory Nerve in Children

This study aimed to (1) investigate the effect of GJB2 and SLC26A4 gene mutations on auditory nerve function in pediatric cochlear implant users and (2) compare their results with those measured in implanted children with idiopathic hearing loss. Participants included 20 children with biallelic GJB2 mutations, 16 children with biallelic SLC26A4 mutations, and 19 children with idiopathic hearing loss. All subjects except for two in the SLC26A4 group had concurrent Mondini malformation and enlarged vestibular aqueduct. All subjects used Cochlear Nucleus devices in their test ears. For each subject, electrophysiological measures of the electrically evoked compound action potential (eCAP) were recorded using both anodic- and cathodic-leading biphasic pulses. Dependent variables (DVs) of interest included slope of eCAP input/output (I/O) function, the eCAP threshold, and eCAP amplitude measured at the maximum comfortable level (C level) of the anodic-leading stimulus (i.e., the anodic C level). Slopes of eCAP I/O functions were estimated using statistical modeling with a linear regression function. These DVs were measured at three electrode locations across the electrode array. Generalized linear mixed effect models were used to evaluate the effects of study group, stimulus polarity, and electrode location on each DV. Steeper slopes of eCAP I/O function, lower eCAP thresholds, and larger eCAP amplitude at the anodic C level were measured for the anodic-leading stimulus compared with the cathodic-leading stimulus in all subject groups. Children with GJB2 mutations showed steeper slopes of eCAP I/O function and larger eCAP amplitudes at the anodic C level than children with SLC26A4 mutations and children with idiopathic hearing loss for both the anodic- and cathodic-leading stimuli. In addition, children with GJB2 mutations showed a smaller increase in eCAP amplitude when the stimulus changed from the cathodic-leading pulse to the anodic-leading pulse (i.e., smaller polarity effect) than children with idiopathic hearing loss. There was no statistically significant difference in slope of eCAP I/O function, eCAP amplitude at the anodic C level, or the size of polarity effect on all three DVs between children with SLC26A4 mutations and children with idiopathic hearing loss. These results suggested that better auditory nerve function was associated with GJB2 but not with SLC26A4 mutations when compared with idiopathic hearing loss. In addition, significant effects of electrode location were observed for slope of eCAP I/O function and the eCAP threshold. GJB2 and SLC26A4 gene mutations did not alter polarity sensitivity of auditory nerve fibers to electrical stimulation. The anodic-leading stimulus was generally more effective in activating auditory nerve fibers than the cathodic-leading stimulus, despite the presence of GJB2 or SLC26A4 mutations. Patients with GJB2 mutations appeared to have better functional status of the auditory nerve than patients with SLC26A4 mutations who had concurrent Mondini malformation and enlarged vestibular aqueduct and patients with idiopathic hearing loss.

Recommendations for Measuring the Electrically Evoked Compound Action Potential in Children With Cochlear Nerve Deficiency.

This study reports a method for measuring the electrically evoked compound action potential (eCAP) in children with cochlear nerve deficiency (CND). This method was developed based on experience with 50 children with CND who were Cochlear Nucleus cochlear implant users. This method includes three recommended steps conducted with recommended stimulating and recording parameters: initial screen, pulse phase duration optimization, and eCAP threshold determination (i.e., identifying the lowest stimulation level that can evoke an eCAP). Compared with the manufacturer-default parameters, the recommended parameters used in this method yielded a higher success rate for measuring the eCAP in children with CND. The eCAP can be measured successfully in children with CND using recommended parameters. This specific method is suitable for measuring the eCAP in children with CND in clinical settings. However, it is not suitable for intraoperative eCAP recordings due to the extensive testing time required.

Incomplete partition typeIII revisited-long-term results following cochlear implant.

Incomplete partition typeIII (IPIII) is defined by amissing lamina cribrosa between the cochlea and the internal auditory canal (IAC). Cochlear implantation (CI) may result in an insertion of the electrode array into the IAC. The aim of this study is to evaluate CI surgery protocols, long-term audiological outcome, mapping and electrophysiological data after CI in IPIII patients. Nine IPIII patients were implanted with perimodiolar electrode arrays between 1999 and 2014; eight of them were included in this study. We evaluated mapping data, stapedius reflexes, electrode impedances and ECAP thresholds. We matched them with 3CI patients each with normal cochlear morphology regarding sex, age, side, implant type and surgical date. Speech discrimination was evaluated with the Oldenburger sentence test for adults, Göttingen audiometric speech test for children and the Freiburger monosyllabic word test. 3years after CI IPIII patients showed asignificant increase in pulse width, calculated electric load and electrode impedances in basal electrodes. Intraoperative electrically-evoked stapedius reflexes could be measured in all patients. Speech recognition scores were lower than average scores for matched patients, but without statistical significance. The significant increase of pulse width, electric load and electrode impedances of basal electrodes over time seem to be characteristic for IPIII patients probably occurring due to fibrosis and neurodegeneration of the cochlear nerve. The long term audiological results are stable. Intraoperative imaging and stapedius reflexes are highly recommended to control the right position of the electrode array.

Incomplete partition typeIII revisited-long-term results following cochlear implant. German version

Incomplete partition typeIII (IPIII) is defined by amissing lamina cribrosa between the cochlea and the internal auditory canal (IAC). Cochlear implantation (CI) may result in an insertion of the electrode array into the IAC. The aim of this study is to evaluate CI surgery protocols, long-term audiological outcome, mapping and electrophysiological data after CI in IPIII patients. Nine IPIII patients were implanted with perimodiolar electrode arrays between 1999 and 2014; eight of them were included in this study. We evaluated mapping data, stapedius reflexes, electrode impedances and ECAP thresholds. We matched them with 3CI patients each with normal cochlear morphology regarding sex, age, side, implant type and surgical date. Speech discrimination was evaluated with the Oldenburger sentence test for adults, Göttingen audiometric speech test for children and the Freiburger monosyllabic word test. 3years after CI IPIII patients showed asignificant increase in pulse width, calculated electric load and electrode impedances in basal electrodes. Intraoperative electrically-evoked stapedius reflexes could be measured in all patients. Speech recognition scores were lower than average scores for matched patients, but without statistical significance. The significant increase of pulse width, electric load and electrode impedances of basal electrodes over time seem to be characteristic for IPIII patients probably occurring due to fibrosis and neurodegeneration of the cochlear nerve. The long term audiological results are stable. Intraoperative imaging and stapedius reflexes are highly recommended to control the right position of the electrode array.

Comparison of the Objective Measures and Behavioral Responses in Cochlear Implant Users Implanted with CI422: A Preliminary Study

Objectives: The aim of the present study is to investigate the relationship between the eSRT and eCAP thresholds with the behavioral comfortable levels in CI users implanted with CI422. Materials and Methods: There were 10 CI user included in the study with mean age at evaluation 20.47. five electrodes were selected from different regions of cochlea for comparison. For these five electrodes, behavioral C levels were determined with Custom Soundâ 5.2 Fitting Software and eCAP and eSRT thresholds were obtained with Custom Soundâ EP 5.2. Results: Correlations analysis was done between behavioral C levels and eSRT or eCAP separately. For E22, behavioral C level was positively correlated with eSRT (r=.772; p= .009; p&amp;lt;.01). However, there was no correlational relation with eCAP. For E1, behavioral C level was positively correlated with both eSRT (r=0.785; p=.007; p&amp;lt; .01) and eCAP (r=0.812; p=.004; p&amp;lt;.01). there was not any correlational relation between eSRT and eCAP except E1. Behavioral C levels was compared with ECAP and ESRT with related-samples Wilcoxon test. Behavioral C levels for all electrodes are statistically significantly different from eSRT levels. Conclusion: This study is the first study that investigates the objective measures and behavioral method in adults with CI422 implants. Both eCAP and eSRT can be used in CI fitting but eSRT levels are significantly higher than the behavioral C levels. In order to provide adequate stimulation the combination of the objective measures and behavioral methods was considered to be the best option.

Influence of stimulus presentation rate on intraoperative ECAP thresholds in cochlear implant users

Objective: The objective is to evaluate the influence of the presentation rate on intraoperative ECAP thresholds in cochlear implant users.Design: The design was data on the ECAP thresholds (t-NRT) as well as the behavioural T- and C-levels have been collected in CI patients of a quaternary otologic referral centre. Measurements of the tNRT thresholds were performed intraoperatively for 250 Hz and 80 Hz presentation rates and correlated to the stabilised T- and C-levels measured at the 5th fitting session, 4-6 months after surgery.Study sample: There was a study sample of 35 consecutive CI patients. All patients were users of the Nucleus 24RECA (Freedom) or Nucleus CI512 cochlear implants with the Contour Advance-of-Stylet electrode.Results: The result showed that the t-NRT thresholds were higher for the 250 Hz pulse rate typically used during the intraoperative stimulation under general anaesthesia than for the 80 Hz rate used typically during the postoperative fitting sessions. This difference was more pronounced for the basal electrodes where it exceeded 10 current levels (CL). Pearson’s correlation coefficients between the t-NRT-measurements and the stabilised T- and C-levels r ranged between 0.34 and 0.47.Conclusion: In conclusion, the magnitude of the ECAP thresholds (t-NRT) recorded intraoperatively depends significantly on the stimulus presentation rate.

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

Objective: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.Design:This was an unmasked, descriptive, and observational study with a cross-over (repeated measures) design that included 13 subjects. We recorded eCAPs on three electrode contacts: in the base, middle, and apex of the cochlea at 10 stimulus intensities. Per stimulus level, 256 eCAP waveforms were recorded. eCAP thresholds were determined by constructing AGFs and linear extrapolation to zero-amplitude. The precision of the eCAP threshold was calculated as the SD using a Monte Carlo simulation, as a function of the number of waveform averages.Results:The SD of the eCAP threshold was reduced by approximately the square root of two when the number of averages in the eCAP waveforms was doubled. The precision was significantly better when the slope of the AGF was steeper and was more favorable in the cochlear base than in the apex. Precision was better when AP averaging was used. Absolute eCAP threshold did not significantly affect precision. At the default number of 32 waveform averages in the Advanced Bionics system, we report a median SD of the eCAP threshold of 2 to 3 μA, with a range of 1 to 11 μA across the cochlea. Previous studies have shown that the total error, based on the 95% confidence bounds of the linear extrapolation, can be as high as −260 to +120 μA.Conclusions:The median variability in the eCAP threshold proved to be small compared with the total variability introduced by the linear extrapolation method. Yet there was substantial intersubject variability. Therefore, we recommend monitoring the SD during eCAP recording to facilitate informed decisions when to terminate waveform collection. From a precision perspective, AP averaging is preferable over FM as it has better precision, while fewer recordings are needed, making it the more time-efficient method of the two.

Evaluation of ECAP thresholds, T and C levels in children with sequential bilateral cochlear implants

Aim: The aim of the present study was to compare the values in threshold (T) and comfortable (C) stimulation levels as well as the neural response telemetry (NRT) measurements obtained on the first and the second cochlear implant in children with sequential bilateral cochlear implantation (CI). Material and Methods: Thirty children with sequential bilateral CI between February 2007 and July 2018 were randomly selected. The mean age of the subjects was 7.0 years (age range: 3.3–15.2 years). The NRT thresholds, T levels, and C levels in the electrode (E) 22, E16, E11, E6, and E1 were retrospectively compared for the latest program on the first CI (CI1), and the second CI (CI2) in the postoperative 1st, 3rd, and 6th-month follow-up visits. The duration of daily use of the speech processor on both side was also compared.Results: Twelve male and eightteen female subjects with sequential bilateral CI, were participated in the present study. The median age at CI1 was 15 months and 5 years 5 months for CI1 and CI2 respectively. There was no significant difference between the threshold NRT (tNRT) levels between two ears. The mean tNRT levels were obtained 166 CL and 179 CL in E22 and E1 respectively. The tNRT levels were found higher on the basal electrode rather than the apical electrode (p=0.02). The changes in the T and C levels were significant in 1st, 3rd, and 6th-month follow-up visits on the CI2 side (p=0.000). The mean daily usage time of the sound processor was found 12.05 and 9.62 hours on CI1 and CI2 respectively. Conclusion: In children with sequential CI, the electrical stimulation levels were similar between ears. The present study shows the programming outcomes during the follow-up in children with sequential bilateral CI. Keywords: Hearing loss; cochlear implant; sequential surgery; bilateral cochlear implantation; neural response telemetry.

The Precision of eCAP Thresholds Derived From Amplitude Growth Functions.

An amplitude growth function (AGF) shows the amplitude of an electrically evoked compound action potential (eCAP) as a function of the stimulation current. AGFs can be used to derive the eCAP threshold, which represents the minimum amount of current needed to elicit a measurable eCAP. eCAP thresholds have been widely used clinically to, for example, assist with sound processor programming. However, no eCAP precision has been included to date. The aim of this study was to investigate the precision of eCAP thresholds and determine whether they are precise enough for clinical use. The study is retrospective, and the data comprised 826 AGFs, intraoperatively measured in 111 patients implanted with a HiRes90K cochlear implant (Advanced Bionics). For each AGF, the eCAP threshold was determined using two commonly used methods: linear extrapolation (LE) toward the x axis and detection of the last visible (LV) eCAP. Subsequently, the threshold confidence interval (TCI) of each eCAP threshold was calculated to serve as a metric for precision, whereby a larger TCI means a lower precision or reliability. Additionally, the eCAP thresholds results were compared with most recent behavioral fitting thresholds (T profile) to put the eCAP threshold analysis in clinical context. Thereby, the association between eCAP and behavioral thresholds was calculated, both for all subjects together (group analysis) and, in contrast to previous studies, within individual subjects. Our data show that the TCIs were larger with the LE method than with the LV method. The eCAP thresholds estimated by the LE method were systematically smaller than those estimated by the LV method, while the LE thresholds with the smallest TCIs correlated best with the LV thresholds. Correlation analysis between eCAP and behavioral thresholds revealed correlation coefficients of r = 0.44 and r = 0.54 for the group analysis of LE and LV thresholds, respectively. Within individual subjects, however, the correlation coefficients varied from approximately -1 to +1 for both LE and LV thresholds. Further analysis showed that across subjects, the behavioral thresholds fell within the TCIs of the eCAP threshold profiles. This study shows that eCAP thresholds have an uncertainty that can be estimated using TCIs. The size of the TCI depends on several factors, for example, the threshold estimation method and measurement conditions, but it is often larger than one would expect when just looking at the threshold values. Given these large TCIs, future research on eCAP thresholds should be accompanied by a measure of precision to correctly apply eCAP thresholds in clinical practice. Comparing our eCAP threshold results with T profiles indicates that the eCAP thresholds are possibly not precise enough to predict T profiles.

Use of Electrically Evoked Compound Action Potentials for Cochlear Implant Fitting: A Systematic Review.

The electrically evoked compound action potential (eCAP) is widely used in the clinic as an objective measure to assess cochlear implant functionality. During the past decade, there has been increasing interest in applying eCAPs for fitting of cochlear implants. Several studies have shown that eCAP-based fitting can potentially replace time-consuming behavioral fitting procedures, especially in young children. However, a closer look to all available literature revealed that there is no clear consensus on the validity of this fitting procedure. This study evaluated the validity of eCAP-based fitting of cochlear implant recipients based on a systematic review of the recent literature. The Preferred Reporting Items for Systematic Reviews and Meta-Analyses were used to search the PubMed, Web of Science, and Cochrane Library databases. The term "eCAP" was combined with "cochlear implants," "thresholds," and "levels," in addition to a range of related terms. Finally, 32 studies met the inclusion criteria. These studies were evaluated on the risk of bias and, when possible, compared by meta-analysis. Almost all assessed studies suffered from some form of risk of bias. Twenty-nine of the studies based their conclusion on a group correlation instead of individual subject correlations (analytical bias); 14 studies were unclear about randomization or blinding (outcome assessment bias); 9 studies provided no clear description of the populations used, for example, prelingually or postlingually implanted subjects (selection bias); and 4 studies had a high rate of loss (>10%) for patients or electrodes (attrition bias). Meta-analysis of these studies revealed a weak pooled correlation between eCAP thresholds and both behavioral T- and C-levels (r = 0.58 and r = 0.61, respectively). This review shows that the majority of the assessed studies suffered from substantial shortcomings in study design and statistical analysis. Meta-analysis showed that there is only weak evidence to support the use of eCAP data for cochlear implant fitting purposes; eCAP thresholds are an equally weak predictor for both T- and C-levels. Based on this review, it can be concluded that research on eCAP-based fitting needs a profound reflection on study design and analysis to draw well-grounded conclusions about the validity of eCAP-based fitting of cochlear implant recipients.

Responsiveness of the Electrically Stimulated Cochlear Nerve in Children With Cochlear Nerve Deficiency.

This study aimed to (1) investigate the responsiveness of the cochlear nerve (CN) to a single biphasic-electrical pulse in implanted children with cochlear nerve deficiency (CND) and (2) compare their results with those measured in implanted children with normal-size CNs. Participants included 23 children with CND (CND1 to CND23) and 18 children with normal-size CNs (S1 to S18). All subjects except for CND1 used Cochlear Nucleus cochlear implants with contour electrode arrays in their test ears. CND1 was implanted with a Cochlear Nucleus Freedom cochlear implant with a straight electrode array in the test ear. For each subject, the CN input/output (I/O) function and the refractory recovery function were measured using electrophysiological measures of the electrically evoked compound action potential (eCAP) at multiple electrode sites across the electrode array. Dependent variables included eCAP threshold, the maximum eCAP amplitude, slope of the I/O function, and time-constants of the refractory recovery function. Slopes of I/O functions were estimated using statistical modeling with a sigmoidal function. Recovery time-constants, including measures of the absolute refractory period and the relative refractory period, were estimated using statistical modeling with an exponential decay function. Generalized linear mixed-effect models were used to evaluate the effects of electrode site on the dependent variables measured in children with CND and to compare results of these dependent variables between subject groups. The eCAP was recorded at all test electrodes in children with normal-size CNs. In contrast, the eCAP could not be recorded at any electrode site in 4 children with CND. For all other children with CND, the percentage of electrodes with measurable eCAPs decreased as the stimulating site moved in a basal-to-apical direction. For children with CND, the stimulating site had a significant effect on the slope of the I/O functions and the relative refractory period but showed no significant effect on eCAP threshold and the maximum eCAP amplitude. Children with CND had significantly higher eCAP thresholds, smaller maximum eCAP amplitudes, flatter slopes of I/O functions, and longer absolute refractory periods than children with normal-size CNs. There was no significant difference in the relative refractory period measured in these two subject groups. In children with CND, the functional status of the CN varied along the length of the cochlea. Compared with children with normal-size CNs, children with CND showed reduced CN responsiveness to electrical stimuli. The prolonged CN absolute refractory period in children with CND might account for, at least partially, the observed benefit of using relatively slow pulse rate in these patients.

Comparing eSRT and eCAP measurements in pediatric MED-EL cochlear implant users

Introduction: Electrically evoked compound action potentials (eCAP) and electrically evoked stapedius reflexes are the most frequently used objective measurements for programming a cochlear implant (CI) audio processor. Objective methods are particularly beneficial for children and CI users that encounter difficulties in providing feedback. In this study, we compared the threshold and the slope of the eCAP amplitude growth function with the electrically evoked stapedius reflex threshold (eSRT) in pediatric CI users. Furthermore, the duration times required to perform eCAP and eSRT recordings were compared.Methods: During a regular fitting session, 52 pediatric CI users with recordable eSRTs having MED-EL devices (MED-EL GmbH, Innsbruck, Austria) were programmed using the eSRT fitting method. The eCAP thresholds and the slopes of the amplitude growth function were measured across one apical, one medial, and one basal electrode contact.Results: There was a weak to medium correlation between eCAP thresholds and eSRTs. The eCAP threshold profile did not correlate with the eSRT profile. Typically ECAP thresholds were at a lower stimulation charge than eSRTs with only 4/152 being higher. An eCAP threshold was found on 152/156 electrode contacts with eSRTs. On average, the eCAP measurements took 4.2 times longer to record per electrode than eSRT measurements (median durations 35 s vs. 120 s).Conclusion: eSRTs were significantly higher than eCAP thresholds and eSRT and eCAP profiles were generally different from each other reducing the clinical relevance of eCAP testing for setting MCLs across the array. Additionally, the eSRT measurements were faster to record than the eCAP threshold and slope determination measurements.

Outcome of cochlear implantation in children with enlarged vestibular aqueduct (EVA) and mondini dysplasia (incomplete partition type II)

Background Congenital inner ear abnormality is a major cause of sensorineural hearing loss in children, about 20% of children with congenital sensorineural hearing loss (SNHL) have associated malformations of the temporal bone, and increased experience in cochlear implantation has led to more children with abnormal cochleo-vestibular anatomy submitted to this procedure. Aim To evaluate the outcome of cochlear implantation in cases with enlarged vestibular aqueduct (EVA) and Mondini deformity (incomplete partition type II) following cochlear implantation and comparing the results with cochlear implant cases without inner ear anomalies. Patients and methods 69 children all less than 6 years of age, CI surgeries underwent from April 2014 to December 2015 at the National Hearing & Speech institute (HSI) Giza-Egypt. Eight patients were congenital prelingual severe to profound hearing loss with enlarged vestibular aqueduct (EVA) and Mondini deformity (incomplete partition type II) Isolated EVA was detected in four cases, two cases with bilateral incomplete partition type II (Mondini deformity) and two cases with bilateral incomplete partition II (Mondini deformity) associated with dilated vestibule & vestibular aqueducts bilaterally with short lateral, SCC (semicircular canal), Beside those 8 cases, a random sample (16 control cases) . The ECAP thresholds determined with neural response telemetry (NRT) or Auditory response threshold (ART) software provide a good starting point for locating the behavioral T and C levels. Auditory skills were evaluated before start of rehabilitation and after 6 months of rehabilitation using LittlEARS Questionnaire and Auditory Checklists and compared to the auditory skills of other cochlear implantees with normal inner ear. Results: This study showed that the auditory skills and audiological performance of children with congenital ear anomalies developed over a period of 6 months after cochlear implantation, in a similar manner to those of young children with radiologically normal inner ears. Conclusion Cochlear implantation can be successfully performed in children with enlarged vestibular aqueduct (EVA) and Mondini dysplasia (incomplete partition type II) .These children and their parents can expect significant auditory benefits from this intervention.

Systematic review of compound action potentials as predictors for cochlear implant performance.

The variability in speech perception between cochlear implant users is thought to result from the degeneration of the auditory nerve. Degeneration of the auditory nerve, histologically assessed, correlates with electrophysiologically acquired measures, such as electrically evoked compound action potentials (eCAPs) in experimental animals. To predict degeneration of the auditory nerve in humans, where histology is impossible, this paper reviews the correlation between speech perception and eCAP recordings in cochlear implant patients. PubMed and Embase. We performed a systematic search for articles containing the following major themes: cochlear implants, evoked potentials, and speech perception. Two investigators independently conducted title-abstract screening, full-text screening, and critical appraisal. Data were extracted from the remaining articles. Twenty-five of 1,429 identified articles described a correlation between speech perception and eCAP attributes. Due to study heterogeneity, a meta-analysis was not feasible, and studies were descriptively analyzed. Several studies investigating presence of the eCAP, recovery time constant, slope of the amplitude growth function, and spatial selectivity showed significant correlations with speech perception. In contrast, neural adaptation, eCAP threshold, and change with varying interphase gap did not significantly correlate with speech perception in any of the identified studies. Significant correlations between speech perception and parameters obtained through eCAP recordings have been documented in literature; however, reporting was ambiguous. There is insufficient evidence for eCAPs as a predictive factor for speech perception. More research is needed to further investigate this relation. Laryngoscope, 2016 127:476-487, 2017.

ECAP analysis in cochlear implant patients as a function of patient's age and electrode-design

IntroductionElectric compound action potentials (ECAPs) provide information about the nerve's and device's function in and after cochlear implantation. In general, lower ECAP values are expected to generate better results. Aim was an analysis of ECAPs in the course of time as a function of the patient's age and electrode design. Patients and methodsBetween 2008 and 2013, 168 patients of eight defined age groups were included into the investigation. NRTs were measured intraoperatively, after 6 and after 12months. ResultsThe intraoperative mean value of ECAP was 174.14CL (current level) and decreased after 6months to 156.38CL. Highest ECAPs were achieved intraoperatively in the clusters “younger than 18months” (181.04CL) and “older than 80 years” (190.45CL). CI 422 showed apparently higher ECAP thresholds (182.69) during surgery than CI 24 RE (171.47) and CI 512 (170.64). ConclusionECAPs are a well-established method to get information about the CI's and nerve's function during and after surgery. After initial higher values NRTs decrease after 6months and remain stable in the following controls. Very young and older patients tend to have higher thresholds than middle-aged groups. Perimodiolar electrodes are significantly attached to lower values because there is a closer nerve–electrode interaction.