Comparison of EAP thresholds with MAP levels in the nucleus 24 cochlear implant: data from children

OBJECTIVE: 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. DESIGN: 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. RESULTS: 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. CONCLUSIONS: 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 relationship between EAP and EABR thresholds and levels used to program the nucleus 24 speech processor: data from adults

OBJECTIVE: 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. DESIGN: 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. RESULTS: 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. CONCLUSIONS: 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.     

Evaluation of streamlined programming procedures for the Nucleus cochlear implant with the Contour electrode array

OBJECTIVE: The objective of this study was to evaluate streamlined programming procedures for the Nucleus cochlear implant system with the Contour electrode array. DESIGN: Phase 1 involved an examination of the clinical MAPs for the first 103 recipients implanted with the Contour electrode array in the Melbourne Cochlear Implant Clinic, to examine the ability to predict the entire MAP based on a smaller number of clinically determined T- and/or C-levels. In phase 2, a subset of the streamlined procedures was selected and clinically evaluated, using speech perception and subjective preference measures. In the first study, the clinical MAP was compared with a MAP based on interpolating across three behavioral T-levels and three behavioral C-levels in a group of newly implanted subjects. The second study investigated the use of a single interpolated profile as the basis to creating the entire MAP. Initial evaluation compared the clinical MAP with two streamlined MAPs, one in which the C-level profile was derived from interpolation across a subset of T-levels and one in which the T-level profile was derived from interpolation across a subset of C-levels. In this case, the interpolated profile was based on five behavioral measures. Subsequently, the use of either three or a single T-level measure as the basis for the interpolated T-level profile was evaluated. Eighteen subjects, who were experienced with the clinical MAP before enrollment in the study, participated in the initial evaluation. The subjects were selected to include a group whose RMS deviation from clinical MAP levels, as determined in Phase 1, was greater than that of the wider population. RESULTS: The Phase 1 analysis showed that as expected, larger differences were observed between the clinical and derived MAP levels as interpolation was applied across fewer measured electrodes and that the use of a single interpolated profile to create the entire MAP resulted in the greatest deviation. No significant group mean difference was found in speech perception scores for newly implanted subjects when mapped with the clinical versus the streamlined MAP based on three behavioral T- and three behavioral C-level measures. For some individual subjects, scores were higher with the streamlined MAP. Subjective reports from the comparative performance questionnaire were consistent with these findings. No significant group mean difference in speech perception scores was found in comparing the clinical MAP with the streamlined MAPs based on a single interpolated T- or C-level profile created from five behavioral measures. Individual effects were observed; however, there was no consistent finding across subjects. The use of three rather than five behavioral T-level measures in the procedure did not result in significantly lower group mean scores; however, significantly poorer scores were obtained for three of the 10 individual subjects. The use of a MAP based on a single behavioral measure did result in poorer speech perception scores when compared with the MAP based on five behavioral T-level measures. These findings were consistent with subjective results from the performance questionnaires administered to determine preference for program across a range of listening situations. CONCLUSIONS: Two streamlined programming procedures are recommended for use in the clinical setting: (1) interpolating across three measured T-levels and three measured C-levels and (2) interpolating across five measured T- or C-levels and using the interpolated profile for fitting of the alternative profile.     

人工耳蜗植入术后神经反应遥测阈值与行为阈值及舒适阈的比较

目的　通过对人工耳蜗植入术后不同患者神经反应遥测 (neuralresponsetelemetry,NRT)阈值与行为反应阈值 (T level,T级 )及舒适阈 (C level,C级 )的比较 ,试图为小年龄或不能给予准确反应的患者客观估算人工耳蜗植入术后行为反应T、C级提供依据。方法　受试对象为使用NucleusCI2 4M型多导人工耳蜗系统的 70例患者。共测试 3 2 9个电极。测试软件为NRT2 0 4版本。NRT阈值的测试采用单极刺激方式 (monopolarstimulationmode) ,分别测试每一位患者的第 3、5、10、15、2 0号电极。T级和C级的测试均于NRT测试同日进行。结果　 70例患者的 3 2 9个电极的NRT波形检出率为 92 7%。同一患者不同编号电极的NRT反应幅值和阈值及不同患者同一编号电极的NRT反应幅值和阈值均存在差异。NRT阈值的均值介于行为反应T级和C级的均值之间。NRT阈值及T、C级的数值自蜗底至蜗顶呈下降趋势。结论　NRT阈值、T级和C级的个体差异较大 ,尚不能根据NRT阈值对T级和C级进行准确的判断。但NRT技术可为不能配合术后调试的儿童患者的行为反应T、C级的估算提供客观的方法。NRT这一新技术仍有待于改进     

Relation between neural response telemetry thresholds, T- and C-levels, and loudness judgments in 12 adult nucleus 24 cochlear implant recipients

OBJECTIVE: The primary purpose of this study was to determine if the contour of visual (vNRT) or predicted (tNRT) neural response telemetry (NRT) thresholds across electrodes could predict the contour of behaviorally programmed T-levels (minimum stimulation) and/or C-levels (maximum stimulation) across electrodes for well-fit MAPs. The secondary purpose was to determine the relation between NRT thresholds and loudness judgments obtained at the subject's MAP rate (250, 900, 1200, or 1800 pulses per second [pps]) and the NRT stimulus rate (80 pps). DESIGN: Twelve adult Nucleus 24 cochlear implant recipients participated in the study. The T- and C-levels from a preferred MAP, which had been worn for a minimum of 3 mo, were used in this study. Electrically evoked compound action potentials were measured on 11 active electrodes with NRT software (v3.0). Ascending loudness judgments from first hearing to maximum acceptable loudness were completed on these electrodes with the subject's preferred MAP rate stimulus, using the R126 (v.2.0) software and with an 80 pps rate stimulus, using the NRT software (v3.0). All measures were repeated approximately 1 mo later to determine their reliability. RESULTS: The reliability of the behavioral and objective measures was very high from the first to the second half of the study. The mean tNRT thresholds had a lower reliability (r = 0.73) than vNRT thresholds (r = 0.91). The loudness judgment dynamic range was notably different between rates. The NRT rate (80 pps) stimulus resulted in the narrowest dynamic range followed by increasingly wider dynamic range as the MAP rate increased. The NRT thresholds had a stronger correlation with loudness judgments made with the NRT rate stimulus than with the MAP rate stimulus. The group mean NRT thresholds were significantly correlated with C-levels (vNRT r = 0.69) (tNRT r = 0.66) but not T-levels. The relation between NRT thresholds and T- and C-levels varied for different MAP rates, with the NRT thresholds being closest to the C-levels for the 250 pps MAP rate. Each subject's vNRT thresholds and MAP levels were examined by fitting a third-order polynomial to the data. This analysis revealed significant variability demonstrating that no one fit predicts T- and C-levels well for all subjects. CONCLUSIONS: The results of this study provide important insight into the relation between NRT thresholds and loudness judgments for different stimulation rates and T- and C-levels at various MAP rates. The loudness judgment dynamic range and MAP dynamic range (T- and C-levels) varied notably for different stimulation rates. As a result, the relation of NRT thresholds to these measures also varied with stimulation rate. Overall, the mean vNRT thresholds fell higher in the loudness judgment dynamic range than the tNRT thresholds. Mean NRT thresholds fell between the judgments of medium soft and maximum acceptable loudness for all stimulation rates. Mean vNRT thresholds fell above C-levels, whereas almost half of tNRT thresholds fell just below C-levels. However, the relation between NRT thresholds and C-levels varied substantially for different MAP stimulation levels. In addition, there is substantial individual variability in the relation between NRT thresholds and MAP levels that is not reflected in the group data. The prediction of the contour of T- and C-levels from the contour of NRT thresholds across electrodes would not be appropriate for half of the subjects. Therefore, great care should be taken when applying a fitting rule that incorporates NRT thresholds without considering these individual differences. For adults who can provide appropriate loudness judgments and threshold responses it appears to be most efficient to primarily use behavioral measures to create MAPs.     

Intra-operative recordings of electrically evoked auditory nerve action potentials in young children by use of neural response telemetry with the nucleus C124M cochlear implant.

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.     

人工耳蜗植入术后神经反应遥测阈值与行为阈值及舒适阈的比较

目的 通过对人工耳蜗植入术后不同患者神经反应遥测（neural response telemetr,NRT)阈值与行为反应阈值（T-level,T级）及舒适阈（C-level,C级）的比较，试图为小年龄或不能给予准确反应的患者客观估算人工耳蜗植入术后行为反应T、C级提供依据。方法 受试对象为使用Nucleus CI24M型多导人工耳蜗系统的70例患者。共测试329个电极。测试软件为NRT2.04版本。NRT阈值的测试采用单极刺激方式（monopolar stimulation mode)，分别测试每一位患者的第3、5、10、15、20号电极。T级和C级的测试均于NRT测试同日进行。结果 70例患者的329个电极的NRT波形检出率为92.7%。同一患者不同编号电极的NRT反应幅值和阈值及不同患者同一编号电极的NRT反应幅值和阈值均存在差异。NRT阈值的均值介于行为反应T级和C级的均值之间。NRT阈值及T、C级的数值自蜗底至蜗顶呈下降趋势。结论 NRT阈值、T级和C级的个体差异较大，尚不能根据NRT阈值对T级和C级进行准确的判断。但NRT技术可为不能配合术后调试的儿童患者的行为反应T、C级的估算提供客观的方法。NRT这一新技术仍有待于改进。     

Cochlear implantees: Analysis of behavioral and objective measures for a clinical population of various age groups

Abstract

Introduction

As of 2014 more than 1200 patients have received a cochlear implant (CI) at Oslo University Hospital (OUS) and approximately half of them have been children. The data obtained from these patients have been used to develop a comprehensive database for a systematic analysis of several objective measurements and programming measurements. During the past 10 years, we have used an objective measurements protocol for our CI surgeries. Our intra-operative protocol includes: Evoked Compound Action Potentials (ECAP), visually observed Electrically evoked Stapedius Reflex Threshold (ESRT), and electrode impedances. Post-operative (Post-OP) programming sessions typically begin 4–6 weeks after surgery and continue on a scheduled basis. The initial programming data include threshold levels (T-levels) and comfortable levels (C-levels) for the different patient age groups. In this study, we compared initial stimulation levels and stimulation levels after at least 1 year of CI with objective measurements obtained intra-operatively.

Method

This study focused on the development of a comprehensive database of detailed intra-operative objective measures and post-OP programming measurements from a group of 296 CI patients who received the same type of CI and electrode configuration (Cochlear^® Corporation CI with Contour^® electrode). This group included 92 bilateral CI patients. Measurements from 388 CI devices were studied. Patients were divided into 5 different age groups at the age of implantation: 0–2, 2–5, 5–10, 10–20, and above 20 years in order to investigate age-related differences in programming levels and objective measurements. For the comparison analysis we used T- and C-levels obtained after the last day of initial programming and also after at least 1 year implant use. These programming levels were then correlated with some of the intra-operative objective measurements.

Results

T-levels were found to be the lowest for the youngest patient group and increased with age. C-levels varied within age groups and frequency range. Patients above 20 years of age had the highest comfort levels in the low to mid-frequencies (electrodes 22–8) and the lowest comfort levels in the high-frequency range (electrodes 1–7). Correlation coefficients between intra-operative objective measurements and programming levels were found to be in the range of no correlation to moderate correlation. Adult patients had the most significant correlation coefficients between ECAP thresholds and T-levels in the low frequencies. The younger patients aged 10–20 years and 5–10 years had more significant correlations in the higher frequency channels compared to the other age groups. Intra-operative visually observed ESRTs and electrode impedances were not significantly correlated with initial or stable programming levels for the children or adults.

Conclusion

Analyzing initial and follow-up mapping levels from previous patients is very important for a CI Center in terms of quality control. The mean T/C-levels reported in this study can provide guidance to our programming audiologists and help them determine the initial programming levels to be stored in the speech processor, especially for very young patients. Unfortunately intra-operative objective measures in our study, such as ECAP, ESRT, and electrode impedances did not provide statistically significant correlations that may help to predict the programming T- and C-levels for all patients. However, we have observed cases where the intra-operative objective measures of ESRT and TECAP profiles were very similar to an individual's MAP profile. It was not possible, however, to determine why some patients did not have an objective measures profile that was similar to their programming levels profile.     

Effects of the Clarion Electrode Positioning System on auditory thresholds and comfortable loudness levels in pediatric patients with cochlear implants

OBJECTIVE: To evaluate the effects of using the Electrode Positioning System on psychophysical auditory thresholds, most comfortable loudness levels, and electric auditory brainstem response (EABR) thresholds in children with the Clarion version 1.2 cochlear implant. DESIGN: Retrospective analysis. SETTING: Academic tertiary care center. PATIENTS AND METHODS: Clinical records of a series of 25 children who received the Clarion version 1.2 cochlear implant at the University of Minnesota, Minneapolis, between January 1997 and August 1999 were examined. Measures evaluated were psychophysical thresholds (T-levels) and most comfortable loudness levels (M-levels) obtained at the 3-month posthookup audiologic evaluation and EABR thresholds obtained during implant surgery. Relevant threshold measures were available for 24 patients, 11 of whom had received the Clarion spiral electrode and electrode positioner (EP group) and 13 of whom had received the spiral electrode without positioner (non-EP group). The 3 measures (T-levels, M-levels, and EABR thresholds) were compared across groups. In addition, EABR thresholds were compared with T-levels and M-levels within groups. RESULTS: Mean T-levels and M-levels were significantly lower for the EP group than for the non-EP group, and interpatient variability for these measures was considerably smaller in the EP group. Electric auditory brainstem response thresholds were not significantly different for EP vs non-EP patients; however, EABR data were available for only a few non-EP patients. CONCLUSIONS: Use of the electrode positioner results in lower T-levels and M-levels in children with the Clarion version 1.2 cochlear implant, consistent with results of previous studies in adults, and reduces across-patient variability for these measures. It is unclear from the present data whether use of the electrode positioner systematically reduces intraoperative EABR thresholds.     

Estimation of psychophysical levels using the electrically evoked compound action potential measured with the neural response telemetry capabilities of Cochlear Corporation's CI24M device.

OBJECTIVE: The goal of this study was to estimate psychophysical levels using the electrically evoked compound action potential (EAP), measured with the Neural Response Telemetry capabilities of Cochlear Corporation's Nucleus CI24M cochlear implant system. DESIGN: Twelve postlingually deafened adults with at least 3 mo of implant experience with the CI24M were subjects in this study. EAP growth functions were successfully quantified on each active electrode of every subject. Correlation and regression analyses were performed between EAP measures and cochlear implant fitting psychophysics. Other information including performance, etiology and duration of hearing loss, and individual electrode impedance was considered. RESULTS: EAP thresholds were found to be highly correlated with psychophysical thresholds. The rate of EAP growth with increasing stimulation levels was also found to be correlated with the dynamic range of loudness limits and psychophysical thresholds in some subjects. No relationship was evident between EAP measures and speech perception tests. CONCLUSIONS: Information from EAP growth function measurements may be used to estimate psychophysical information used in cochlear implant fitting but not to predict performance with the device.     

Assessment of the functioning of peripheral auditory pathways after cochlear re-implantation in young children using intra-operative objective measures

The intra-operative electrical auditory brainstem response (EABR), electrical stapedius reflex threshold (ESRT) and the early post-operative behavioural threshold level (T-level) were recorded in five children undergoing cochlear re-implantation. The aim of the study was to assess objectively the effect of re-implantation on intra-operative objective measures and to investigate neuronal function. The children were aged between 2.06 years and 4.5 years at first implantation. Following failure of the first device, re-implantation was carried out 1.42-5.52 years later. Characteristics of the EABR and ESRT across the electrode array were typical of the expected pattern of responses on both occasions. In particular, the slopes of the amplitude input/output (I/O) functions for wave eV of the intraoperative EABR were similar for both the first and second implants even though absolute thresholds were generally elevated after re-implantation. This elevation in intra-operative threshold was more pronounced than the change in early post-operative behavioural threshold level for electrical stimulation (T-level). Our findings confirm a high level of neuronal survival after re-implantation. Threshold of the intra-operative EABR at the time of re-implantation greatly underestimates the sensitivity of the subsequent early post-operative T-levels.     

神经反应遥测技术在人工耳蜗术后调试中的应用

目的通过对小儿人工耳蜗植入者术后言语处理器调试中运用NRT（神经反应遥侧）技术效果的分析．探讨NRT在人工耳蜗术后调试中的应用价值。方法选取10例术后主观调试配合欠佳的儿童．用Cochlear公司NRT3．0编程软件进行ECAP波形检测并测定ECAP阈值，利用测试结果判断主观阈值（T-值）和最大舒适阈（C-值），并得出言语处理器映射图（Map）。术后6个月行声场听阈测听。结果86．2％的电极引出ECAP波形，开机调试时反应阈值较小，以后逐渐升高，3～4个月左右闽值逐渐趋于稳定，而且靠近蜗底的阈值比蜗尖高。声场平均听阈为30～40dBSPL。经过言语康复训练，获得良好的效果。结论NRT技术可为术后快速准确地调试言语处理器提供客观依据．     

Toward a method for programming balanced bilateral cochlear implant stimulation levels in children

Abstract

Objectives

In the present study, we investigated differences in stimulation levels between bilateral cochlear implants (CIs) in children and compared these to previously recorded measures of balanced input. We hypothesized that differences in stimulation levels between two CI: (1) will be observed both in behavioral and objective measures, and (2) can help to provide bilateral stimulation levels that are perceived as balanced.

Method

Participants were 19 children who received bilateral CIs sequentially. Behaviorally determined minimum and maximum stimulation levels from the first (CI-1) and second (CI-2) CIs at an apical electrode (#20) were compared with thresholds of the electrically evoked compound action potential (ECAP) of the auditory nerve and electrically evoked stapedius reflex (ESR).

Results

All four measures were found to be greater when evoked from CI-1 than CI-2 and the dynamic range between behavioral measures was reduced in CI-2 relative to CI-1. Significant correlations were found between differences in behavioral and objective measures; as differences in T-levels between CI-1 and CI-2 increased, so did the differences in ECAP thresholds and a similarly positive relationship was found between C-level differences and ESR threshold differences. Differences in ECAP thresholds between CI-1 and CI-2 were significantly correlated with balanced bilateral levels.

Discussion

Children using two different Nucleus CIs often require different stimulation levels on either side. Although lower levels were needed on the side more recently implanted with newer technology, the dynamic range of input provided on the second side was reduced relative to the more experienced side. Differences in behavioral measures between CI-1 and CI-2 can be partially predicted by objective measures. ECAP thresholds show the best promise for helping to provide balanced bilateral CI input in children.     

A method for determining precise electrical hearing thresholds in cochlear implant users

Objective: A psychoacoustic procedure designed for the precise assessment of perceptional threshold (T-level) in cochlear implant (CI) users is presented. The impact of this procedure on speech perception was investigated. Design: Individual T-level measurements were obtained with the proposed procedure and three different speech processor fitting conditions were applied: (1) fitting familiar to the subject, T-levels unchanged, (2) T-level set to thresholds determined with the new procedure, (3) T-level set to thresholds determined with the new procedure, but T-level is decreased by 10 clinical units (CU). The impact of the different fitting conditions was measured by means of categorical loudness scaling (CLS) and speech perception tests in quiet and noise. Study sample: A prospective study at a tertiary referral university hospital. 18 experienced postlingually deafened cochlear implanted adult subjects. Results: Average sound-field thresholds obtained by CLS were lowest in condition using the new procedure yielding a larger dynamic range with significantly higher speech scores in quiet compared to those with a subject’s commonly used programme, and significantly improved in noise even after reducing T-levels by 10 CU. Conclusion: The precise determination of T-levels by means of the proposed procedure improved performance in several speech recognition tasks. Compared to the default behavioural setting, T-level increased on median by 9 CU. Average speech reception threshold in noise for soft speech levels (50?dB sound pressure level) decreased by 1?dB.     

电诱发听性脑干反应和电诱发镫骨肌反射阈值在内耳畸形儿童人工耳蜗植入术后调机中的运用

目的　探讨内耳畸形小儿人工耳蜗植入手术后,植入体电诱发听性脑干反应（electrically evoked auditory brainstem responses,EABR）、电诱发镫骨肌反射阈值（electrically evoked stapedius reflex threshold,ESRT）的变化特点及规律,以指导术后设备调试。方法　将88例澳大利亚Cochlear Nucleus24型人工耳蜗植入手术患儿分为耳蜗形态正常组与内耳畸形组,测试手术后1年内不同时期EABR和ESRT值,术后1年运用行为测试法检测主观阈值（T值）和最大舒适阈（C值）,分析特点及变化规律。结果  内耳畸形组患儿术后不同时期EABR和ESRT阈值较正常组高（P＜0.05）,两组EABR和ESRT阈值变化趋势相同,总的趋势是低频值较低,高频值较高,术后1年EABR和ESRT阈值逐渐增高;两组EABR与T值显著相关,ESRT与C值显著相关。结论　内耳畸形组人工耳蜗植入手术后EABR和ESRT阈值变化规律及特点与正常组患儿相同,阈值可用于指导内耳畸形人工耳蜗植入者手术后设备的调试。     

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.     

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

ObjectiveTo evaluate the efficacy of using neural response telemetry (NRT) thresholds in predicting behavioural thresholds during programming of cochlear implant in prelingual children.MethodProspective study of 28 cochlear implants implanted with Nucleus 24 cochlear implant. We recorded NRT-thresholds on electrode numbers 1, 6, 11, 16 and 22 of the electrode array in each patient, the neural response thresholds were correlated with the behavioural map after six months of programming the device.ResultsThe mean neural response telemetry level was significantly higher than the mean threshold level (T-level) but lower than the comfortable level (C-level) in all the electrodes tested. NRT levels could statistically significantly predict T behavioural levels and comfortable behavioural levels, p < 0.01. There was a strong positive correlation between comfortable thresholds and neural response telemetry level measurements and behavioural threshold level and neural response telemetry threshold measurements.ConclusionThere is a useful role for neural response telemetry values in predicting the behavioural threshold and comfortable values in prelingual children. Combining the NRT values with behavioural observations can improve the programming of cochlear implants.     

Electrode impedance in adults and children using the Nucleus 24 cochlear implant system

This study measured changes in electrode impedance over time in 19 adults and 29 children implanted with the Nucleus 24 cochlear implant system, using common ground and three monopolar modes of stimulation, over a series of time intervals. Impedances increased from the intraoperative to the initial fitting session, decreased during the initial fitting session and for the following week, and were then stable. Impedances were lowest for the common ground mode, while for the monopolar modes, impedances were related to the surface area of the return electrode. Impedances for children were higher than those for adults at the initial fitting session and for the following three weeks. The clinically measured impedance values increased in a basal-to-apical direction. When these data were corrected for differences in electrode surface area, impedances decreased in a basal-to-apical direction. Impedances were influenced by whether the electrodes were stimulated or unstimulated. Adults with higher electrode impedances tended to have lower hearing thresholds and comfortable listening levels, but this did not appear to clearly be the case for children.     

人工耳蜗术后编程中神经反应遥测阈值及行为T值的比较分析

目的 了解人工耳蜗术后神经反应遥测(NRT)阈值的变化,NRT与行为T值之间的相关性,以及长期行为T值的变化,为人工耳蜗植入术后的患儿编程提供帮助。 方法 20例接受Nucleus CI24R型多导人工耳蜗植入的患儿,在开机时及6个月调试时对1、11、20号电极进行NRT阈值测试,通过NRT值进行电子耳蜗程序设置;开机后1年和2年对患儿进行行为T值测试,并设置程序;收集开机时及6个月的NRT值分别与1年及2年的行为T值比较。 结果 1号电极开机时和6个月时NRT相互比较差异无统计学意义,11号和22号电极开机时和6个月时NRT差异有统计学意义,三对电极1年与2年行为T值差异都无统计学意义;开机时NRT阈值与行为T值的相关关系中:开机时NRT阈值与行为T值只有22号电极呈正相关,其余两电极中无相关关系。6个月NRT阈值与行为T值的相关关系中:1号电极6个月NRT阈值与行为T值均为正相关;22号电极开机6个月NRT值与1年行为T值为正相关,其他无相关关系。 结论 各电极NRT阈值自开机时基本保持稳定,NRT阈值与行为T值部分电极具有相关性,开机时和最初几次调机时患儿不能配合进行行为测试可以选择NRT阈值来参考调试耳蜗;1年和2年的行为T值也基本稳定,说明患儿术后1年能较好配合行为T值测试,对于配合较好者的患儿可以适当延长调试时间。     

语前聋儿童人工耳蜗植入后的调机与声场评估

目的 调查语前聋儿童人工耳蜗植入术后声场主观测听阈值和对应T值的变化趋势。方法 28例人工耳蜗植入儿童。年龄3—6岁。无耳蜗畸形，植入后电极阻抗测试完全正常。对开机后3月、6月和1年时间的声场主观测听阈值与T值的变化进行了统计分析。结果 声场测听阈值在开机1年中呈逐渐降低趋势，开机1年时声场测听的听力水平较3个月和6个月有明显提高（P〈0．05）。植入者术后一年声场主观测听（啭音）听阈为15—35dB HL，听力水平较术前有明显提高。28例植入者T值在开机一年后明显低于六个月和三个月的水平（P〈0．05）。结论 开机后一年内T值和声场测听阈值都呈逐渐下降趋势．并且与3个月和6个月的水平差异具有统计学意义。植入者在熟悉适应了电声信号后，可以在刺激电流强度下降的同时获得更好的听力。