Summary of results using the nucleus CI24M implant to record the electrically evoked compound action potential

OBJECTIVE: This study outlines a series of experiments using the neural response telemetry (NRT) system of the Nucleus CI24M cochlear implant to measure the electrically evoked compound action potential (EAP). The goal of this investigation was to develop a protocol that allows successful recording of the EAP in a majority of CI24M cochlear implant users. DESIGN: Twenty-six postlingually deafened adults participated in this study. A series of experiments were conducted that allowed us to examine how manipulation of stimulation and recording parameters may affect the morphology of the EAP recorded using the Nucleus NRT system. RESULTS: Results of this study show consistent responses on at least some electrodes from all subjects. Cross-subject and cross electrode variations in both the growth of the response and the temporal refractory properties of the response were observed. The range of stimulus and recording parameters that can be used to record the EAP with the Nucleus NRT system is described. CONCLUSIONS: Using the protocol outlined in this study, it is possible to reliably record EAP responses from most subjects and for most electrodes in Nucleus CI24M cochlear implant users. These responses are robust and recording these responses does not require that the subject sleep or remain still. Based on these results, a specific protocol is proposed for measurement of the EAP using the NRT system of the CI24M cochlear implant. Potential clinical implications of these results are discussed.     

Neural response telemetry with the nucleus CI24M cochlear implant

OBJECTIVES: To review our intraoperative and postoperative testing protocol for cochlear implant patients. This study describes the methodologies and applications of a new technique called neural response telemetry (NRT) for the Nucleus CI24M cochlear implant system. NRT uses radiofrequency telemetry technology to measure the action potentials of the auditory nerve. STUDY DESIGN: We have developed a specific protocol for intraoperative testing of the implant device before, during, and after implantation. This includes device integrity tests, visual detection of electrical stapedius muscle reflexes (VESR), and NRT. METHODS: Our methodologies use the commercial software (Windows-based Diagnostic and Programming System [WIN-DPS] and NRT) for the Nucleus CI24M. We describe the details of our protocol used on all of the patients (14 adults and 14 children) who received CI24M implants at Mayo Clinic (Rochester, MN). Our protocol correlates the NRT threshold with the behavioral responses for each patient on at least four electrodes. RESULTS: From August 1, 1998, to December 31,1998, we completed electrode integrity tests, NRT, and VESR testing intraoperatively on 12 patients with the Nucleus CI24M. We have measured normal implant function on all 28 of our CI24M patients with one exception. One of our children had a device failure after approximately 4 months as a result of head trauma. We have also obtained NRT results from an additional 10 patients postoperatively. CONCLUSIONS: The measurement of device and electrode array function is quite simple with the CI24M software. These measurements can be obtained intraoperatively as well as postoperatively. We conclude that VESR and NRT measurements can be very helpful in programming for patients with cochlear implants, especially children, because they provides us with target settings for the speech processor.     

神经反应遥测技术在人工耳蜗植入术中的监测应用

目的：探讨在人工耳蜗植入术中能快速,准确地判断人工蜗装置的完好性和患者客观听觉反应的监测方法。方法：在40例患儿人工耳蜗植入术中先测定电极阻抗,然后使用神经反应遥测技术（neural response telemetry,NRT)监测6个电极的电诱发听神经复合动作电位（electrically evoked auditory nerve compound action potentials,ECAP)。结果：患儿所有电极阻抗正常,ECAP的检出率分别为97．5％（39例／40例）和92．1％（221个电极／240个电极）,其中33例内耳无畸形的患儿所有198个测试电极中有195个电极测出清晰的ECAP波形（98．5％）,7例内耳Mondini畸形患者共42个测试电极中有26个电极测得ECAP波形（61．9％）,两组之间差异有极显著性,靠近耳蜗底回（高频区）的电极比靠近蜗尖（低频区）的电极具有较高的ECAP反应阈值的ECAP饱和阈值。结论：NRT技术可以简便,快速和准确地判断患者的听神经反应,可望成为术中常规监测方法。内耳Mondini畸形是影响ECAP检出的重要因素。     

Nucleus人工耳蜗弯电极和直电极植入后的心理物理指标比较

目的对比Nucleus CI 24导Contour弯电极与Nucleus CI 24导直电极植入后的电阻阻抗、刺激阈值和舒适阈。方法植入澳大利亚NucleuS人工耳蜗的患者分为2组,1组（19例）植入Nucleus CI 24导Contour电极阵列（弯电极）,另1组（11例）植入CI 24M电极阵列（直电极）。所有患者耳蜗植入术后15天开机调试,并于开机时及开机后1周、1月、3月分别记录各电极的电阻、刺激闽值和最大舒适阈。结果开机后由于Nucleus 24直电极的刺激阈值呈上升趋势,3月和6月时弯电极的阈值明显低于直电极阈值,且差异有统计学意义（P〈0．05）。开机1周、1月和6月2组的舒适阈接近。开机后弯电极和直电极的电阻值接近。结论Nucleus CI 24导Contour弯电极的刺激阈值稳定,刺激阈和舒适阈之间动态范围较宽。     

Mandarin speech perception in nucleus CI 24 implantees using MAPs based on neural response telemetry

The purpose of this study is to compare speech perception performance in Mandarin-speaking Nucleus CI24 implantee using standard behavior MAPs and NRT-based MAPs. Eight Nucleus CI24 users (5 years and older) participated in the study. They all fulfilled the following criteria: (1) behavioral MAP and NRT thresholds can be reliably obtained; (2) had more than 18 functioning electrodes; (3) had at least 6 months experience using CI. All subjects received speech evaluation under three different MAPs: a traditional behavioral MAP, a MAP predicted from the NRT thresholds of the E22 (electrode 22), E19, E15, E11, E8, E5, E1 and a combined MAP based on the information of NRT thresholds and behavioral threshold/comfortable levels of the E11. The speech evaluation package included word recognition test in quiet, in noise, and a Mandarin sentence test in quiet. Results showed that three MAPs are similar in some subjects, but different in other subjects. Compared to the NRT MAPs, the combined MAPs are more similar to the behavioral MAPs. There was no significant difference in the mean score of the word recognition test in quiet, in noise and sentence test under these three MAP conditions. In conclusion, although the behavioral MAPs and the NRT-based MAPs are not identical, the speech performance of Mandarin-speaking CI24 implantee using MAPs predicted from NRT thresholds appeared to be no worse than the traditional behavioral MAPs. Therefore, in certain cases that behavioral MAPs are difficult to obtain (such as in very young or multiple handicapped children), NRT-based MAPs may serve reliably as an initial estimation.     

Dual electrode stimulation using the nucleus CI24RE cochlear implant: electrode impedance and pitch ranking studies

OBJECTIVE: The first aim of the study was to determine the reduction in electrode impedances using dual electrode stimulation compared with single electrode stimulation in the new Nucleus CI24RE receiver-stimulator. The CI24RE is connected to the Nucleus 22-electrode intracochlear array. Dual electrode stimulation is produced by electrically coupling two adjacent single electrodes. The second aim was to determine whether dual electrode stimulation produced pitch percepts that were intermediate to the pitch of the two adjacent single electrodes. DESIGN: Eight postlingually hearing-impaired adults with severe to profound loss, implanted with the CI24RE, participated in the study. Electrode impedances were measured by using the standard telemetry function of the system. A pitch ranking task was used to measure pitch for dual and single electrodes. Seven sets of three electrodes along the electrode array were tested. Each set of electrodes consisted of a dual electrode and the two adjacent single electrodes. Pitch ranking was measured using a two-alternative forced choice procedure, with the three electrodes in each set paired with each other as AB and BA pairs. The subject indicated which of the two stimuli had the higher pitch. Random variation in current level was used to remove any loudness cues. RESULTS: The average electrode impedance was 38.6% lower for dual electrodes compared with single electrodes. Three subjects were able to successfully rank the three electrodes in each set in the expected tonotopic order for all seven sets of electrodes along the array. Three other subjects were able to rank sets of electrodes in the tonotopic order for most of the tested positions on the array. The remaining two subjects gave more variable pitch ranking across positions along the array, although successful tonotopic ranking was demonstrated for several sets of electrodes. CONCLUSIONS: Dual electrode stimulation with the CI24RE receiver-stimulator produced systematically lower electrode impedances and was capable of producing pitch percepts that were intermediate to those produced by the corresponding adjacent single electrodes. This makes available up to 43 channels of stimulation from 22 single electrodes.     

Speech perception in nucleus CI24M cochlear implant users with processor settings based on electrically evoked compound action potential thresholds

Adjusting the speech processor of a cochlear implant, per electrode, to the individual's response is a laborious task that may interfere with a user-friendly start of implant-mediated hearing, particularly in children. This research concerns the possibility of processor adjustment based on a profile derived from measurements of the electrically evoked compound action potential (ECAP) thresholds across the electrode array, followed by adjustment of the overall level of the profile to the hearing threshold and maximum comfortable loudness level using live voice. The results for CVC word lists show that speech perception is quite insensitive to the threshold setting of the speech processor. On average, the speech score does not decrease by more than 10% when, with the new method, the threshold setting comes out so much lower that the dynamic range has doubled. In contrast, the speech score appears to be sensitive to an increase of the maximum high-frequency stimulation settings for the basal electrodes, resulting in lower scores at these higher settings. The correlation between the overall ECAP thresholds and conventionally measured subjective thresholds is weak (r = 0.64). However, the correlation between the slopes of these threshold curves is satisfactory (r = 0.82). The correlation between the ECAP thresholds and the maximum stimulation levels is poor, both with respect to overall level and slope (r = 0.39 and 0.36, respectively). Applicability of the ECAP threshold in processor adjustment could not be demonstrated in this study. Prediction of the most critical factor in speech perception, the slope of the maximum stimulation curve, from the ECAP thresholds is poor. However, considering habituation to the initial processor setting of at least 6 months, the small decrease in the CVC scores with the new setting suggests that a more user-friendly adjustment procedure can be developed.     

神经反应遥测技术在人工耳蜗植入术中的监测应用

目的探讨在人工耳蜗植入术中能快速、准确地判断人工耳蜗装置的完好性和患者客观听觉反应的监测方法.方法在40例患儿人工耳蜗植入术中先测定电极阻抗,然后使用神经反应遥测技术(neuralresponsetelemetry,NRT)监测6个电极的电诱发听神经复合动作电位(electricallyevokedauditorynervecompoundactionpotentials,ECAP).结果患儿所有电极阻抗正常,ECAP的检出率分别为97.5%(39例/40例)和92.1%(221个电极/240个电极).其中33例内耳无畸形的患儿所有198个测试电极中有195个电极测出清晰的ECAP波形(98.5%).7例内耳Mondini畸形患者共42个测试电极中有26个电极测得ECAP波形(61.9%),两组之间差异有极显著性.靠近耳蜗底回(高频区)的电极比靠近蜗尖(低频区)的电极具有较高的ECAP反应阈值和较高的ECAP饱和阈值.结论NRT技术可以简便、快速和准确地判断患者的听神经反应,可望成为术中常规监测方法,内耳Mondini畸形是影响ECAP检出的重要因素.     

Development of a new test for speech audiometry in children and results in CI children

BACKGROUND: Speech audiometry plays an important role for hearing evaluation in children. Hearing impaired children, such as those with cochlear implant (CI) who frequently undergo testing, learn the test words by heart. Furthermore, the standard tests use words of former time. PATIENTS AND METHODS: Using the most frequently words of modern children's literature a speech assessment test was developed for children between 1 to 8 years. The material was first evaluated on normal hearing children. In a second step the phoneme and word perception scores of 35 CI children were measured using 60 - 100 dB SPL according to the most comfortable level (MCL) in free sound field. RESULTS: The performance-intensity function for the single words were highly comparable with those of the Freiburger or G?ttinger speech perception test. The average speech reception threshold in CI children was 44 % (test I), 36 % (test II), 63 % (test III) and 69 % (test IV), respectively. Compared to the Mainzer and G?ttinger speech perception test the new words were more difficult to understand than those of the known tests. However, a statistically significant difference could be noted only for test II. CONCLUSIONS: The new developed "Würzburger speech perception test" appears to be a useful additional tool for the evaluation of hearing impaired children in addition to the standard test procedures.     

Nucleus24型人工耳蜗使用者电诱发听神经复合动作电位的测定

目的 :探讨电诱发听神经复合动作电位 (ECAP)的特点及在人工耳蜗临床中的应用价值和意义。方法 :应用NRT(neuralresponsetelemetry)软件 ,通过体外言语处理器和耳蜗内的植入电极系统 ,采用单极模式电极刺激和近场记录方法 ,对 37例NucleusCI2 4M装置使用者进行ECAP的记录。对其中 12例使用者做了行为测试。结果 :87.6 %的使用者记录到ECAP波形。分析了有行为阈值的 12例测试者的ECAP阈值和行为阈值的关系 ,二者之间存在显著的相关性。结论 :ECAP的检出率高且波形稳定可靠 ,在临床人工耳蜗装置的调试中可作为对行为测试的补充 ;对于年幼儿童和首次开机的患者的调试尤其重要     

Electrical impedance measurements with the CI24M cochlear implant for a child with Mondini dysplasia

Electrical impedance measurements can give useful information about the status of individual electrodes of a cochlear implant. Impedances within the normal range (when measured in the common ground mode of stimulation) suggest that current flow occurs in the tissue and fluid of the cochlea. Low impedance measurements may suggest that particular electrodes are short circuiting, whereas high impedances might be due to a broken electrode wire or an electrode only in contact with air. In the case discussed, low impedance measurements were recorded intra-operatively from a child with Mondini dysplasia on electrodes 1-13 of a Nucleus CI24M device. Post-operatively the impedances had returned to the expected range and were comparable with other patients implanted with the CI24M device. Possible reasons for this are discussed. It was thought that impedances were low intra-operatively due to a larger-than-normal proportion of fluid surrounding the electrode array, rather than short circuits occurring along the array, as suggested by the dps7 software.     

Normative findings of electrically evoked compound action potential measurements using the neural response telemetry of the Nucleus CI24M cochlear implant system

One hundred and forty-seven adult recipients of the Nucleus 24 cochlear implant system, from 13 different European countries, were tested using neural response telemetry to measure the electrically evoked compound action potential (ECAP), according to a standardised postoperative measurement procedure. Recordings were obtained in 96% of these subjects with this standardised procedure. The group results are presented in terms of peak amplitude and latency, slope of the amplitude growth function and ECAP threshold. The effects of aetiological factors and the duration of deafness on the ECAP were also studied. While large intersubject variability and intrasubject variability (across electrodes) were found, results fell within a consistent pattern and a normative range of peak amplitudes and latencies was established. The aetiological factors had little effect on the ECAP characteristics. However, age affected ECAP amplitude and slope of the amplitude growth function significantly; i.e., the amplitude is higher in the lowest age category (15-30 years). Principal component analysis of the ECAP thresholds shows that the thresholds across 5 electrodes can be described by two factors accounting for 92% of the total variance. The two factors represent the overall level of the threshold profiles ('shift') and their slopes across the electrode array ('tilt'). Correlation between these two factors and the same factors describing the T- and C-levels appeared to be moderate, in the range of 0.5-0.6.     

Neural response telemetry results with the nucleus 24 contour in a perimodiolar position.

OBJECTIVE: The purpose of the study was to analyze changes in neural response telemetry using the Cochlear Nucleus 24 Contour before and after stylet removal in a human model. STUDY DESIGN: Prospective study. SETTING: Tertiary referral center. PATIENTS: Twelve patients (23-72 years old) undergoing cochlear implantation, using the Nucleus 24 Contour implant, secondary to congenital and age-related hearing loss. INTERVENTION: Cochlear implantation with Cochlear Nucleus 24 Contour implant. MAIN OUTCOME MEASURE: Neural response telemetry thresholds were recorded initially with the stylet in and then with the stylet out during the implant procedure. RESULTS: Stimulus levels to obtain neural response telemetry threshold after stylet removal were statistically lower after the stylet was removed. CONCLUSION: The Nucleus 24 Contour achieves a perimodiolar position once the stylet is removed, and this leads to reduction in the current required to elicit a threshold neural response telemetry response.     

Adaptation of the electrically evoked compound action potential (ECAP) recorded from nucleus CI24 cochlear implant users

OBJECTIVE: This study had three main goals. The first goal was to assess the extent to which neural adaptation varied across cochlear implant users. The second goal was to determine whether adaptation at the level of the auditory nerve was correlated with word recognition ability. The third goal was to determine whether peripheral neural adaptation had an impact on the relationship between the electrically evoked compound action potential (ECAP) thresholds and MAP levels. DESIGN: Neural response telemetry software was used to record the ECAP in 21 Nucleus cochlear implant users. A series of 110 ECAP recordings were made over a 5-min period at three different stimulation rates: 15, 80, and 300 Hz. The stimulation levels used to record this series of responses were held constant at or near the level the subject identified as his or her maximum comfort level (C-level) for the 300-Hz stimulation rate. Consistent decreases in ECAP amplitude as measured from the beginning to the end of the 5-min stimulation interval were interpreted as evidence of neural adaptation. Regression analysis procedures were then used to assess the relationship between neural adaptation and word recognition. RESULTS: Significant levels of adaptation were observed for all 21 subjects at stimulation rates of 80 and 300 Hz. Little or no adaptation was observed over the 5-min recording period when the 15-Hz rate was used. The amount of adaptation was greatest at the 300-Hz rate and varied substantially across cochlear implant users. No relationship between the amount of adaptation and word recognition was found. Neither was the degree of adaptation shown to influence the relationship between ECAP thresholds recorded at low rates and the levels used to program the speech processor. CONCLUSIONS: Cochlear implant users experienced varying degrees of long-term adaptation in response to continuous electrical stimulation. The effects of adaptation on the ECAP were apparent even at stimulation rates as low as 80 Hz. Although variations in the amount of adaptation are likely to reflect cross-subject differences in the status of the auditory nerve, no predictable relationship was found between these physiologic measures of peripheral neural function and either word recognition or the relationship between ECAP thresholds and MAP levels.     

Objective measurements of auditory nerve recovery function in nucleus CI 24 implantees in relation to subjective preference of stimulation rate

OBJECTIVE: Setting the optimal rate of stimulation for individual cochlear implant recipients is critical to the successful functional outcome of cochlear implantation. In the absence of an objective methodology, cochlear implants are currently fitted by means of a time-consuming (and therefore expensive) trial-and-error process of limited accuracy. The aim of this study was to evaluate a possible relationship between the patient's subjectively preferred stimulation rate and an objective measurement of auditory nerve recovery time. MATERIAL AND METHODS: Eleven recipients of Nucleus CI 24 implants initially fitted with a speech processor using the ACE speech-coding strategy at a rate of 900 Hz were introduced to 2 other stimulation rate options, 1200 and 1800 Hz, at 2 different fitting sessions and asked to choose their preferred rate. Preferences were compared with objective measurements of auditory nerve recovery time obtained using the refractory recovery function of neural response telemetry. RESULTS: The auditory nerve recovery time for individuals with a subjective preference for a slow stimulation rate was longer than that for individuals who preferred a fast stimulation rate, with significant differences between the 2 groups for 3 tested electrodes (7, 11 and 15): p = 0.024, 0.009 and 0.03, respectively (Mann-Whitney test). CONCLUSION: The association observed between the subjective stimulation rate preference and measurements of auditory nerve recovery time indicates that the measured auditory nerve recovery time can be used as a reliable predictor for setting up a basic stimulation rate of a particular individual's map, thus reducing the cost of the technology and significantly increasing its effectiveness.     

Objective measurements of auditory nerve recovery function in nucleus CI 24 implantees in relation to subjective preference of stimulation rate

OBJECTIVE: Setting the optimal rate of stimulation for individual cochlear implant recipients is critical to the successful functional outcome of cochlear implantation. In the absence of an objective methodology, cochlear implants are currently fitted by means of a time-consuming (and therefore expensive) trial-and-error process of limited accuracy. The aim of this study was to evaluate a possible relationship between the patient's subjectively preferred stimulation rate and an objective measurement of auditory nerve recovery time. MATERIAL AND METHODS: Eleven recipients of Nucleus CI 24 implants initially fitted with a speech processor using the advanced combination encoders speech-coding strategy at a rate of 900 Hz were introduced to 2 other stimulation rate options, 1200 and 1800 Hz, at 2 different fitting sessions and were asked to choose their preferred rate. Preferences were compared with objective measurements of auditory nerve recovery time obtained with the refractory recovery function of neural response telemetry. RESULTS: The auditory nerve recovery time for individuals with a subjective preference for a slow stimulation rate was longer than that for individuals who preferred a fast stimulation rate, with significant differences between the 2 groups for 3 of the tested electrodes (Nos. 7, 11 and 15): p = 0.024, 0.009 and 0.03, respectively (Mann-Whitney test). CONCLUSIONS: The association observed between subjective stimulation rate preference and measurements of auditory nerve recovery time indicates that the measured auditory nerve recovery time can be used as a reliable predictor for setting up a basic stimulation rate of a particular individual's map, thus reducing the cost of the technology and significantly increasing its effectiveness.     

Objective measurements of auditory nerve recovery function in nucleus CI 24 implantees in relation to subjective preference of stimulation rate

Objective Setting the optimal rate of stimulation for individual cochlear implant recipients is critical to the successful functional outcome of cochlear implantation. In the absence of an objective methodology, cochlear implants are currently fitted by means of a time-consuming (and therefore expensive) trial-and-error process of limited accuracy. The aim of this study was to evaluate a possible relationship between the patient's subjectively preferred stimulation rate and an objective measurement of auditory nerve recovery time.

Material and Methods Eleven recipients of Nucleus CI 24 implants initially fitted with a speech processor using the advanced combination encoders speech-coding strategy at a rate of 900 Hz were introduced to 2 other stimulation rate options, 1200 and 1800 Hz, at 2 different fitting sessions and were asked to choose their preferred rate. Preferences were compared with objective measurements of auditory nerve recovery time obtained with the refractory recovery function of neural response telemetry.

Results The auditory nerve recovery time for individuals with a subjective preference for a slow stimulation rate was longer than that for individuals who preferred a fast stimulation rate, with significant differences between the 2 groups for 3 of the tested electrodes (Nos. 7, 11 and 15): p=0.024, 0.009 and 0.03, respectively (Mann–Whitney test).

Conclusions The association observed between subjective stimulation rate preference and measurements of auditory nerve recovery time indicates that the measured auditory nerve recovery time can be used as a reliable predictor for setting up a basic stimulation rate of a particular individual's map, thus reducing the cost of the technology and significantly increasing its effectiveness.     

Retrospective study of intra-operative testing with the Nucleus CI24M cochlear implant and use of the back-up device

The combined use of integrity testing (IT) and impedance telemetry (ImTe) intra-operatively is evaluated. One hundred and fifty children implanted with the Nucleus device were studied. In 81% of patients, normal results were obtained on all electrodes from both ImTe and IT. In seven cases where the back-up device was used, the intra-operative analysis of the device and subsequent postoperative quality assurance testing did not always correlate. In conclusion, intra-operatively, only ImTe is needed to verify the function of the implant if all impedance values are normal. However, in the case of abnormal ImTe results, additional IT data provide valuable assistance with the decision of whether to leave the implant in place or to use the backup device.     

Optimizing dynamic range in children using the nucleus cochlear implant

OBJECTIVE: The aim of this study was to investigate the benefits of the preprocessing scheme "Adaptive Dynamic Range Optimization" (ADRO) in children using Nucleus cochlear implants. Previous research with adults indicates improved speech perception in quiet and improved sound quality in everyday listening environments with the ADRO scheme. DESIGN: Children were given 4 wk of take-home experience with ADRO, with a minimum of 2 wk in which ADRO was "locked-in." After 1 wk of ADRO use and again after 4 wk of ADRO use, Bench-Kowal-Bamford (BKB) sentence perception in quiet at a low input level of 50 dB SPL (unweighted root mean square) and sentence perception in noise were compared with the child's everyday (Standard) program and the ADRO program. Children also rated the loudness of a variety of environmental sounds and indicated which program provided the best hearing in a variety of everyday listening situations. RESULTS: On average, BKB sentence perception in quiet at 50 dB SPL was significantly better with the ADRO program compared with the Standard program. The group mean improvement was 8.60%. Similarly, group mean scores for BKB sentences presented at 65 dB SPL in multitalker babble were significantly higher with the ADRO program (an improvement of 6.87%). The ADRO program was the preferred program in 46% of the listening situations, whereas the Standard program was preferred in 26% of situations. Everyday sounds were not unacceptably loud with ADRO. CONCLUSIONS: There was an ADRO benefit for this group of children in quiet and in noise. These findings suggest that young children would benefit from the ADRO programming option being locked in along with other processor settings in the SPrint processor once their MAP levels have stabilized. Some older children and teenagers may choose to use ADRO selectively for specific listening situations.