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

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.

Dynamic Range and Neural Response Threshold in Cochlear Implant Mapping Can Be Useful in Predicting Prognosis Related to Postoperative Speech Perception

BACKGROUND AND OBJECTIVES

To analyze mapping changes in dynamic range (DR) and neural response threshold (NRT) as prognostic factors for cochlear implant (CI). To analyze whether postoperative speech perception performance could be predicted using DR change and initial NRT.

SUBJECTS AND METHODS

The speech comprehension data of 33 patients with CI were retrospectively analyzed after 1, 3, 6, and 12 months of device use. All subjects were adult, postlingually hearing-impaired, and Cochlear Nucleus CI users. Speech perception performance was evaluated using aided pure tone audiometry, consonant, vowel, one-word, two-word, and sentence tests.

RESULTS

The averages of initial NRT and DR changes were 197.8±25.9 CU (104-236) and 22.2±18.4 CU (-15-79), respectively. The initial DR was 40.8±16.6 CU. The postoperative DR was 50.3±16.4 CU at 3 months, 58±12.3 CU at 6 months, and 62.9±10.4 CU at 12 months. A gradual increase of DR was observed during the first year of CI. Compared with the initial DR, significant increases in DR were observed at 3 (p<0.05), 6 (p<0.001), and 12 (p<0.001) months. Compared with initial speech performance outcomes, a significant gain in all performance outcomes was achieved at 12 months (p<0.001).

CONCLUSIONS

Patients with low NRT after CI surgery could initially set DR to a wider range and had better final speech perception outcomes. Conversely, patients with high NRT after CI surgery had to set up a gradual increase in DR while adjusting the T-C level, and the final speech perception outcomes were worse. DR and NRT, the main CI mapping variables, can help predict prognosis related to speech perception outcomes after CI surgery. In conclusion, the post-CI speech perception is better with a lower initial NRT, wider final DR, or younger age.

Comparison of Intraoperative Neural Response Telemetry Results and Postoperative Neural Response Telemetry Results in Case of Children with Congenital Bilateral Severe to Profound Sensorineural Hearing Loss Undergoing Single Sided Cochlear Implantation

Aim and Objectives

This study is designed to compare the Intra Operative Neural Response Telemetry (NRT) results with Post-Operative NRT results of the cochlear implanted children, to assess the importance of Intra Operative NRT thresholds in device activation and/or switch on of the audio processor and to evaluate the importance of Intra and post operative AutoNRT results in predicting behavioural thresholds during mapping of prelingual Cochlear Implanted children.

Materials and methods

A total of thirty (30) children (16 boys, 14 girls) with congenital Bilateral (B/L) severe to profound Sensorineural hearing loss (SNHL) were included in this study. Children between the age range of 12 to 60 months were participated in this study. All the participants were implanted with Nucleus 24 cochlear implant system. In each patient, the intra operative NRT-thresholds were measured for all 22 active electrodes. Then Intra Operative NRT thresholds were correlated with Post-Operative NRT thresholds at the time of switch on and the behavioural map after six months of switch on of the device (Audio Processor).

Results

There is a significant enhancement observed in thresholds of postoperative NRT responses which were raised or absent during intraoperative session. There is a gain in NRT thresholds marked after 6 months of postoperative follow up in comparison with first measurement at the time of Switch On of the device but the change not that significant. During postoperative mapping, there was a significant positive correlation noticed between neural response telemetry level measurements and behavioural threshold level.

Conclusion

Absent or elevated NRT responses during intraoperative testing for some electrodes especially basal electrodes does not mean that electrode is out of order or outside the cochlea, because an improvement in NRT thresholds usually occurs postoperatively. In case of children with congenital B/L severe to profound SNHL, the NRT values have a very useful role in predicting the behavioural thresholds. Combination of NRT values with behavioural thresholds and observations of Auditory Verbal Therapist can help in providing best suitable Map to the recipient.

Supplementary Information

The online version contains supplementary material available at 10.1007/s12070-022-03284-x.

Chronic cochlear implantation with and without electric stimulation in a mouse model induces robust cochlear influx of CX3CR1+/GFP macrophages

BACKGROUND

Cochlear implantation is an effective auditory rehabilitation strategy for those with profound hearing loss, including those with residual low frequency hearing through use of hybrid cochlear implantation techniques. Post-mortem studies demonstrate the nearly ubiquitous presence of intracochlear fibrosis and neo-ossification following cochlear implantation. Current evidence suggests post-implantation intracochlear fibrosis is associated with delayed loss of residual acoustic hearing in hybrid cochlear implant (CI) recipients and may also negatively influence outcomes in traditional CI recipients. This study examined the contributions of surgical trauma, foreign body response and electric stimulation to intracochlear fibrosis and the innate immune response to cochlear implantation and the hierarchy of these contributions.

METHODS

Normal hearing CX3CR1+/GFP mice underwent either round window opening (sham), acute CI insertion or chronic CI insertion with no, low- or high-level electric stimulation. Electric stimulation levels were based on neural response telemetry (NRT), beginning post-operative day 7 for 5 h per day. Subjects (n=3 per timepoint) were sacrificed at 4 h, 1,4,7,8,11,14 and 21 days. An unoperated group (n=3) served as controls. Cochleae were harvested at each time-point and prepared for immunohistochemistry with confocal imaging. The images were analyzed to obtain CX3CR1+ macrophage cell number and density in the lateral wall (LW), scala tympani (ST) and Rosenthal's canal (RC).

RESULTS

A ST peri-implant cellular infiltrate and fibrosis occurred exclusively in the chronically implanted groups starting on day 7 with a concurrent infiltration of CX3CR1+ macrophages not seen in the other groups. CX3CR1+ macrophage infiltration was seen in the LW and RC in all experimental groups within the first week, being most prominent in the 3 chronically implanted groups during the second and third week.

CONCLUSIONS

The cochlear immune response was most prominent in the presence of chronic cochlear implantation, regardless of electric stimulation level. Further, the development of intracochlear ST fibrosis was dependent on the presence of the indwelling CI foreign body. An innate immune response was evoked by surgical trauma alone (sham and acute CI groups) to a lesser degree. These data suggest that cochlear inflammation and intrascalar fibrosis after cochlear implantation are largely dependent on the presence of a chronic indwelling foreign body and are not critically dependent on electrical stimulation. Also, these data support a role for surgical trauma in inciting the initial innate immune response.

ARTFit—A Quick and Reliable Tool for Performing Initial Fittings in Users of MED-EL Cochlear Implants

This study assessed the safety and performance of ARTFit, a new tool embedded in MAESTRO, the cochlear implant (CI) system software by MED-EL GmbH (Innsbruck, Austria). ARTFit automatically measures thresholds of the electrically evoked compound action potential (ECAP) to produce initial ‘maps’ (ECAPMAPs), i.e., configuration settings of the audio processor that the audiologist switches to live mode and adjusts for comfortable loudness (LiveECAPMAPs). Twenty-three adult and ten pediatric users of MED-EL CIs participated. The LiveECAPMAPs were compared to behavioral maps (LiveBurstMAPs) and to the participants’ everyday clinical maps (ClinMAPs). Four evaluation measures were considered: average deviations of the maximum comfortable loudness (MCL) levels of the LiveECAPMAPs and the LiveBurstMAPs from the MCLs of the ClinMAPs; correlations between the MCLs of the LiveECAPMAPs (MCL_ecap) and the LiveBurstMAPs (MCL_burst) with the MCLs of the ClinMAPs (MCL_clin); fitting durations; and speech reception thresholds (SRTs). All evaluation measures were analyzed separately in the adult and pediatric subgroups. For all evaluation measures, the deviations of the LiveECAPMAPs from the ClinMAPs were not larger than those of the LiveBurstMAPs from the ClinMAPs. The Pearson correlation between the MCL_ecap and the MCL_clin across all channels was r² = 0.732 (p < 0.001) in the adult and r² = 0.616 (p < 0.001) in the pediatric subgroups. The mean fitting duration in minutes for the LiveECAPMAPs was significantly shorter than for that of the LiveBurstMAPs in both subgroups: adults took 5.70 (range 1.90–11.98) vs. 9.27 (6.83–14.72) min; children took 3.03 (1.97–4.22) vs. 7.35 (3.95–12.77). SRTs measured with the LiveECAPMAPs were non-inferior to those measured with the ClinMAPs and not statistically different to the SRTs measured with the LiveBurstMAPs. ARTFit is a safe, quick, and reliable tool for audiologists to produce ECAP-based initial fitting maps in adults and young children who are not able to provide subjective feedback.

Prediction of Behavioral T/C Levels in Cochlear Implant Patients Based Upon Analysis of Electrode Impedances

BACKGROUND

Fitting cochlear implants in babies and noncooperative patients is cumbersome and time consuming. Therefore, objective parameters have been sought in order to predict the subjective threshold (T) and maximum comfort (C) levels. Measurements of the electrically evoked compound action potentials (ECAPs) have been widely used for this purpose, yet the correlation between these objective measures and the subjective T/C levels is weak to moderate.

PURPOSE

This article aims (1) to evaluate correlations between the subjective parameters of the fitting maps such as thresholds (T level) and maximum comfort levels (C level), the impedance of the electrode contacts, and the ECAP thresholds, and (2) to compare the value of the electrode impedances and the ECAP measures for prediction of the T/C levels.

RESEARCH DESIGN

Case review study in a quaternary otologic referral center.

STUDY SAMPLE

Ninety-eight consecutive CI patients were enrolled. The average age of the patients was 49 years. All patients were users of the Nucleus 24RECA (Freedom, Contour Advance-of-Stylet electrode) cochlear implant.

DATA COLLECTION AND ANALYSIS

Data on impedance of the electrode contacts and the behavioral T/C levels at the first fitting session (2-5 weeks after surgery) and at the 5th fitting session (4-6 months after surgery) have been retrospectively collected in 98 consecutive CI patients. Additionally, the intraoperative impedance values and the ECAP thresholds (tNRT) have been recorded.

RESULTS

Impedances of electrode contacts show significant strong negative correlations with the stabilized T/C levels at 4 to 6 months after implantation and are an important predictor for the behavioral T/C levels. They can explain R ² = 28 to 41% of the variability of the behavioral T/C levels. In multiple regression analysis electrode contact impedances can explain twice as much of the variability of the stabilized T/C levels than the tNRT values. The electrode impedances together with the tNRT values are able to explain R ² = 37 to 40% of the global variability of the T/C levels while the tNRT thresholds solely are able to explain only R ² = 5 to 14% of the T/C levels variability.

CONCLUSION

Impedances of electrode contacts correlate strongly with the stabilized behavioral T/C levels and may be used as an objective measure for fitting of cochlear implants.

A study on relationship between Neural Response Telemetry and behavioural Threshold/Comfort levels in children with cochlear implant

Background

Our study was a prospective, non-randomised, single tertiary care centre study involving 50 children below 10 years, all implanted with Nucleus 24™ cochlear implants to find the relationship between intra-operative NRT (Neural Response Telemetry) values and post-operatively behaviourally obtained Threshold (T) and Comfort (C) levels.

Methods

NRT threshold values were obtained intra-operatively by using Custom Sound EP Software V 4.4™ (Cochlear Corporation). At switch-on after three weeks, behavioural T and C levels were measured based on behavioural responses given by patients using Custom Sound Version 4.4 software™ (Cochlear Corporation). NRT values were also measured at switch-on, 2 months, 3 months and 6 months.

Results

Intra-operative NRT levels (187.96 ± 12.48) were higher than both T (160.63 ± 22.69) and C (181.21 ± 22.41) levels obtained after 3 weeks. In addition, there was a weak correlation of NRT values with T (P value: 0.05, r = 0.391) and C (P value: 0.05, r = 0.390) levels.

Conclusion

NRT is a quick and non-invasive tool to confirm cochlear implant integrity. There is a weak correlation of NRT values with both T and C levels and therefore, intra-operative NRT is a weak predictor for setting both T and C levels at switch-on.

Accuracy of intraoperative electrophysiological testing in confirming correct cochlear implant electrode positions

Objective: To investigate the accuracy of intraoperative electrophysiological studies in detecting incorrectly positioned electrodes in cochlear implant surgery. Study design: A retrospective chart review. Setting: Tertiary referral centre. Patients: In total, 104 consecutive patients with a mean age of 5 years underwent cochlear implant surgery at our centre between January 2012 and December 2013. All patients were implanted with Cochlear Nucleus Freedom implants. Method: A retrospective study to compare intraoperative neural response telemetry (NRT), impedance and electrode position using Stenver's transorbital plain X-ray view. Results: Intraoperative electrophysiological tests for patients with Cochlear Nucleus Freedom implants showed 97% sensitivity and 100% specificity compared with postoperative X-ray imaging. Conclusion: NRT results for the position of cochlear implants were very accurate when checked by X-ray imaging showing that this technique is sufficient in most cases. Stenver's plain X-ray view is needed in complicated cases with abnormal NRT testing or difficult electrode insertion.

Effect of neural adaptation and degeneration on pulse-train ECAPs: A model study

Electrically evoked compound action potentials (eCAPs) are measurements of the auditory nerve's response to electrical stimulation. ECAP amplitudes during pulse trains can exhibit temporal alternations. The magnitude of this alternation tends to diminish over time during the stimulus. How this pattern relates to the temporal behavior of nerve fibers is not known. We hypothesized that the stochasticity, refractoriness, adaptation of the threshold and spike-times influence pulse-train eCAP responses. Thirty thousand auditory nerve fibers were modeled in a three-dimensional cochlear model incorporating pulse-shape effects, pulse-history effects, and stochasticity in the individual neural responses. ECAPs in response to pulse trains of different rates and amplitudes were modeled for fibers with different stochastic properties (by variation of the relative spread) and different temporal properties (by variation of the refractory periods, adaptation and latency). The model predicts alternation of peak amplitudes similar to available human data. In addition, the peak alternation was affected by changing the refractoriness, adaptation, and relative spread of auditory nerve fibers. As these parameters are related to factors such as the duration of deafness and neural survival, this study suggests that the eCAP pattern in response to pulse trains could be used to assess the underlying temporal and stochastic behavior of the auditory nerve. As these properties affect the nerve's response to pulse trains, they are of uttermost importance to sound perception with cochlear implants.

The Precision of eCAP Thresholds Derived From Amplitude Growth Functions

OBJECTIVE

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.

DESIGN

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.

RESULTS

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.

CONCLUSION

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.

Utility of intraoperative computed tomography for cochlear implantation in patients with difficult anatomy

OBJECTIVE AND IMPORTANCE

To describe cases that illustrate the utility of intraoperative computed tomography (CT) in cochlear implantation of patients with difficult temporal bone anatomy.

CLINICAL PRESENTATION

A 2-year-old male with congenital X-linked stapes gusher syndrome and a 2-year-old female with enlarged vestibular aqueduct underwent successful cochlear implantation with the help of intraoperative CT. In the latter case, the initial intraoperative C-arm fluoroscopy suggested malposition of the electrode, however, was not able to provide details for adjustments. In both cases, intraoperative CT changed the insertion technique of the operating surgeon and allowed for improved electrode positioning. A 47-year-old female with polyostotic fibrous dysplasia and a 55-year-old male with post-meningitis near-total cochlear obliteration underwent successful cochlear implantation with confirmation of electrode position with intraoperative CT. In the former case, the image-guided navigation system was also implemented. Finally, a 72-year-old female underwent cochlear implantation during which intraoperative C-arm fluoroscopy suggested intra-cochlear insertion. However, postoperative CT showed the electrode extending into the internal auditory canal (IAC), illustrating the limitations of C-arm fluoroscopy.

INTERVENTION

Intraoperative CT imaging and image-guided navigation system.

CONCLUSION

When faced with challenging temporal bone anatomy, intraoperative CT can provide critical details of the patient's microanatomy that allows for improved localization of the electrode and adjustments in operative techniques for successful cochlear implantation.

A new approach for the determination of ECAP thresholds

BACKGROUND

Electrically evoked compound action potentials (ECAPs) of the auditory nerve are routinely recorded for testing the cochlear implant integrity and its functional connection to the auditory system. The response thresholds derived from ECAP recordings are widely used as a helpful guide in the fitting of the dynamic range of electric stimulation, although they may not always predict the behavioral thresholds of individuals well. Conventionally, this threshold is based on the identification of a minimum N peak and maximum P peak and linear extrapolation of the resulting amplitude growth function (AGF). As an alternative, a new procedure involving numeric signal processing and requiring less user intervention is presented here. Data acquisition: In 12 adults implanted with MED-EL FLEX28 electrodes, two series of ECAPs were recorded immediately after implantation: (i) a full profile involving all 12 channels across the whole stimulus range in steps of 200 current units and (ii) a high resolution section (20 records in the immediate neighborhood of the threshold) of the AGF in one selected channel. Data treatment: It was observed that N and P wave latencies do not depend on stimulus intensity. Fixed time windows were hence defined for stimulus plus noise and noise alone regions. In these windows, the variance of the compound signal representing response and noise is extracted, whereas the noise variance is extracted from the tail of the curve following this time window. The base line is corrected by fitting an exponential function to reduce stimulus or amplifier artifacts. The response threshold is then derived from the response to noise ratio which should exceed the limit of 6 dB.

RESULTS

The ECAP thresholds obtained from the new procedure coincide well with those determined by the conventional linear extrapolation of the AGF and they correlate to a greater degree with psychometric thresholds than the existing approach.

CONCLUSIONS

The new ECAP algorithm looks promising and may reduce the need for user intervention in determining thresholds.

[Objective measures for setting the processors of cochlear implant systems : Use of discrimination functions and consideration of electrode profiles]

BACKGROUND

When setting the electrical stimulation level of cochlear implants during individual adjustment of the speech processor, especially in children, objective measures such as intracochlearly measured electrically evoked compound action potentials (eCAP) and intraoperative observation of electrically elicited stapedial reflexes (eSR) are indispensable. The benefit of these objective measures is based on the correlation between the derived response thresholds and psychometric data.

MATERIALS AND METHODS

The amplitude growth functions of eCAPs were measured intraoperatively for all electrodes in 30 ears of adult patients. The stimulus-dependent incidence of observable eSRs was recorded for all electrodes in 16 ears of adult patients. For evaluation of the data, new algorithms were applied which allowed the determination of thresholds without intervention of the investigator. Essential features were the conversion of observations into binary variables, and the consideration of logistic discrimination functions and their exceedance of a numeric threshold criterion.

RESULTS

Regarding the eCAP data, closer and significant correlations are observed between objective thresholds and psychometric measures in comparison to conventional procedures. Profiles are more efficient than pooled data. Significant correlations are also observed for eSR thresholds, albeit to a lesser extent and without an evident difference between profiles and pooled data.

CONCLUSION

Considering the by no means consistent international literature, the results illustrate the need for a consistent definition of response thresholds and the consideration of electrode profiles.

Relationship Between Electrode-to-Modiolus Distance and Current Levels for Adults With Cochlear Implants

HYPOTHESIS

Electrode-to-modiolus distance is correlated with clinically programmed stimulation levels.

BACKGROUND

Conventional wisdom has long supposed a significant relationship between cochlear implant (CI) stimulation levels and electrode-to-modiolus distance; however, to date, no such formal investigation has been completed. Thus, the purpose of this project was to investigate the relationship between stimulation levels and electrode-to-modiolus distance. A strong correlation between the two would suggest that stimulation levels might be used to estimate electrode-to-modiolus geometry.

METHODS

Electrode-to-modiolus distance was determined via CT imaging using validated CI position analysis software in 137 implanted ears from the three manufacturers holding FDA approval in the United States. Analysis included 2,365 total electrodes, with 1,472 from precurved arrays. Distances were compared to clinically programmed C/M levels that were converted to charge units.

RESULTS

Mean modiolar distance with perimodiolar and lateral wall electrodes was 0.47 and 1.15 mm, respectively. Mean suprathreshold charge values were significantly different between each manufacturer. When combining all data, we found a moderate positive correlation (r = 0.367, p < 0.01) that was driven both by the different charge values across companies, and that the company with the highest mean charge values only offers straight electrode arrays. When grouped by electrode type, however, we found a weak correlation (r = 0.12, p < 0.01) for perimodiolar array electrodes only. When considering a single array type from any one manufacturer, only one was observed where distance mildly predicted charge.

CONCLUSION

Our results suggest that electrode distance minimally contributes to the current level required for suprathreshold stimulation.

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.

Differences between electrically evoked compound action potential (ECAP) and behavioral measures in children with cochlear implants operated in the school age vs. operated in the first years of life

OBJECTIVE

The aim of this study was to identify the differences in the NRT measures, behavioral measures, and their relationship between the group of congenitally deaf children operated in the first years of life and the group of children operated in the school age.

METHODS

The study included 40 congenitally deaf children with cochlear implants divided into two groups. Group 1 was composed of 20 children (mean age at operation 2.3 years, range 1.4-4.6 years) and Group 2 was composed of 20 children (mean age at operation 11.3 years, range 7.0-17.1 years). The ECAP was recorded using the Nucleus 24 neural response telemetry (NRT) system. In each child, the responses were evoked by the apical, middle and basal electrodes. The analyzed parameters were: the ECAP threshold (T-NRT), N1P2 amplitude, N1 latency, slope of the amplitude growth function, response morphology, threshold (T-) level, maximum comfort (C-) level, dynamic range (DR), T-NRT as a percentage of the map DR, the correlation between the T-NRT and the T- and C-levels. The recordings of parameters were performed two years after implantations.

RESULTS

The T-NRT, DR, T-NRT as a percentage of the map DR and the correlation between T-NRT and C-levels were significantly different between both groups of children. There were no statistically significant differences between the groups with respect to the amplitude, latency, slope and morphology recorded using the same electrodes. However, intragroup differences regarding NRT measures and behavioral measures with respect to the position of stimulating electrode were more prominent in Group 2 than in the Group 1.

CONCLUSIONS

Results of this study have also found a great variability of NRT and MAP measures within and across patients in both groups of children, but it was still more pronounced in the group of school children. NRT profile across electrodes follows MAP profiles better in the Group 1 then in the Group 2. Overall findings of NRT and MAP measures are not consistent and unambiguous as we expected, but still suggest potential differences between results in children operated in first years of life, and those operated in school age.