Changes over time in electrical stimulation levels and electrode impedance values in children using the Nucleus 24M cochlear implant

OBJECTIVE: The present study was designed to evaluate changes in psycho-electric parameters, i.e. threshold levels, comfortable levels, dynamic range, and electrode impedance values during the 1st year post-implantation, in children using the Nucleus 24M cochlear implant system. METHODS: The maps of 25 pre-lingual children programmed with ACE strategy in Monopolar 1 + 2 mode were examined at five time points: connection, 1, 3, 6, and 12 months post-initial stimulation. Maps and electrode impedance values were analyzed according to three cochlear segments: basal, medial, and apical. RESULTS: Significant elevations of thresholds, comfortable levels, and dynamic range were found during the first few months of implant use. Specifically, threshold increased and dynamic range widened until the 3 months visit, whereas comfortable levels continued to increase until the 6 months visit, thereafter levels stabilized. Electrode impedance values decreased significantly from connection to the 1-month visit thereafter a stabilization of values was evident. In addition, thresholds and comfortable levels were found to be significantly lower in the apical segment, whereas dynamic range and electrode impedance values did not differ among the cochlear segments. CONCLUSIONS: Significant changes in psycho-electric parameters and electrode impedance values were evident during the first 6 months of implant use. Given the important role of an optimal map for speech perception, frequent programming sessions during the first few months of implant use are essential.     

Electrode failure and device failure in adult cochlear implantation

Abstract

Objectives

To determine the prevalence of cochlear implant electrode failure and the relationship with overall device failure.

Methods

Electrode status was analyzed in 322 functioning and in-use devices from 366 adult cochlear implant patients currently followed at our center. An additional 21 devices that had been explanted were also analyzed. Electrode failure was defined as unacceptably high impedance alone or in combination with aberrant percepts.

Results

At least one electrode had been turned off in 173 devices (54%). Most deactivated electrodes were the basal-most and had been turned off to improve sound quality. Of 437 deactivated electrodes, 33 were considered to have failed and were represented in 22 devices. These 22 devices are still in use (mean: 43.0 ± 29.8 months) without further electrode failures or device failure. There were no statistically significant differences in electrode failure rates among device manufacturers. There were 21 devices explanted of which 10 were due to device failure. One of five hard failures and two of three soft failures had deactivated electrodes prior to explantation. Two failures had no electrode data available.

Discussion

An inherent risk of cochlear implantation, as with all implanted electrical prostheses, is device failure. Failure of individual electrodes has been postulated to represent an early indicator of impending device failure. Our data demonstrate that electrode failure does not necessarily predict impending device failure. Although maps containing deactivated electrodes are fairly common, electrode failure as a reason for bypassing an electrode is rare and is often manageable with programming.     

A longitudinal study of electrical stimulation levels and electrode impedance in children using the Clarion cochlear implant

Conclusions. Electrical stimulation levels and electrode impedance values (EIVs) in children using the Clarion cochlear implant (CI) programmed with CIS strategy stabilized after 3 months of implant use. The data presented here may be useful as a general guideline for the programming of infants and young children and may further be of help for the identification of patients who fall outside the “average” range. Objectives. The purpose of the present study was to evaluate changes in electrical stimulation levels, i.e. threshold (T) levels, comfortable (M) levels, dynamic range (DR), and EIVs during the first 18 months of implant use, in children using the Clarion CI. Materials and methods. The maps of 18 pre-lingual children (mean age at implantation 4.2 years; range 1–8), using the Enhanced Bipolar 1.2 or Bipolar standard electrode with the S-Series speech processor programmed with CIS strategy, were examined at five time points: connection, and 3, 6, 12, and 18 months post-initial stimulation. T levels, M levels, DR and EIVs were analyzed according to four cochlear segments: apical, apical-medial, medial-basal, and basal. Results. During the first 3 months of implant use T levels increased to some extent, whereas M levels and DR increased significantly. From 3 months and through the entire follow-up, T and M levels as well as DR were stable. EIVs of current carrying electrodes decreased significantly from connection to the 3-month visit; thereafter a stabilization of values was evident. Electrical stimulation levels and EIVs did not differ among the cochlear segments during the entire follow-up.     

A longitudinal study of electrical stimulation levels and electrode impedance in children using the Clarion cochlear implant

CONCLUSIONS: Electrical stimulation levels and electrode impedance values (EIVs) in children using the Clarion cochlear implant (CI) programmed with CIS strategy stabilized after 3 months of implant use. The data presented here may be useful as a general guideline for the programming of infants and young children and may further be of help for the identification of patients who fall outside the "average" range. OBJECTIVES: The purpose of the present study was to evaluate changes in electrical stimulation levels, i.e. threshold (T) levels, comfortable (M) levels, dynamic range (DR), and EIVs during the first 18 months of implant use, in children using the Clarion CI. MATERIALS AND METHODS: The maps of 18 pre-lingual children (mean age at implantation 4.2 years; range 1-8), using the Enhanced Bipolar 1.2 or Bipolar standard electrode with the S-Series speech processor programmed with CIS strategy, were examined at five time points: connection, and 3, 6, 12, and 18 months post-initial stimulation. T levels, M levels, DR and EIVs were analyzed according to four cochlear segments: apical, apical-medial, medial-basal, and basal. RESULTS: During the first 3 months of implant use T levels increased to some extent, whereas M levels and DR increased significantly. From 3 months and through the entire follow-up, T and M levels as well as DR were stable. EIVs of current carrying electrodes decreased significantly from connection to the 3-month visit; thereafter a stabilization of values was evident. Electrical stimulation levels and EIVs did not differ among the cochlear segments during the entire follow-up.     

Effect of age,electrode array,and time on cochlear implant impedances

Objectives: To determine the impact of age, electrode array, and time on impedance patterns in cochlear implant (CI) patients.

Methods: A retrospective case review was performed on 98 patients implanted with the CI24RE perimodiolar (PM) and CI422 lateral wall (LW) arrays between 2010 and 2014 to assess impedances at the 1 week and 3–6 month visit after initial stimulation (IS).

Results: With respect to age, impedances were higher in young patients compared to older patients in the middle and apical turns. With time, there were significant reductions in impedances across most electrodes. Electrode array type also had a significant impact on impedance measurements with PM and LW arrays having higher impedances in the basal turn and apical turns, respectively. Furthermore, PM arrays demonstrated significantly lower impedances in the middle and apical turn with time, when compared to LW arrays.

Conclusions: Age, electrode array, and time can independently affect CI impedances. Moreover, we show that PM arrays may be advantageous to LW arrays, due to demonstrated lower impedances in the middle and apical turns long term. Understanding the impact of impedance on speech discrimination and determining the intracochlear processes that contribute to differences in impedance are future research directions.     

Impedance changes in chronically implanted and stimulated cochlear implant electrodes

Abstract

Objectives

Electrode impedance increases following implantation and undergoes transitory reduction with onset of electrical stimulation. The studies in this paper measured the changes in access resistance and polarization impedance in vivo before and following electrical stimulation, and recorded the time course of these changes.

Design

Impedance measures recorded in (a) four cats following 6 months of cochlear implant use, and (b) three cochlear implant recipients with 1.5–5 years cochlear implant experience.

Results

Both the experimental and clinical data exhibited a reduction in electrode impedance, 20 and 5% respectively, within 15–30 minutes of stimulation onset. The majority of these changes occurred through reduction in polarization impedance. Cessation of stimulation was followed by an equivalent rise in impedance measures within 6–12 hours.

Conclusions

Stimulus-induced reductions in impedance exhibit a rapid onset and are evident in both chronic in vivo models tested, even several years after implantation. Given the impedance changes were dominated by the polarization component, these findings suggest that the electrical stimulation altered the electrode surface rather than the bulk tissue and fluid in the cochlea.     

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.     

Lower initial electrode impedances in minimally invasive cochlear implantation

Background: The round window approach and the cochleostomy approach are two widely practiced methods to insert cochlear implant electrode arrays. Yet, there is no consensus on which is more minimally invasive. Objective: To compare the initial electrode impedance (EI) values and the incidence of abnormal electrodes of the round window approach and the cochleostomy approach, and to evaluate the effects of surgical techniques on the intracochlear microenvironment. Material and methods: One hundred and seventy-one patients received a unilateral Nucleus cochlear implant. Eighty-two patients were implanted using the round window approach, and 89 patients were implanted using the cochleostomy approach. EI was measured immediately after closure of the incision. Results: The round window group had lower average initial EI values than the cochleostomy group. For the EI values at each position, statistically significant differences were found in the basal-middle region (Electrode 1–14), but not in the middle-apical region (Electrode 15–22) of the electrode arrays. A lower incidence of high-impedance electrodes was found in the round window group. Conclusions: The round window approach leads to lower initial EI and less disturbance to the intracochlear microenvironment.     

Objective,audiological and quality of life measures with the CI532 slim modiolar electrode

Objectives: To report on electrode array measurements for the Nucleus^® CI532 Slim Modiolar Electrode device including: ECAP thresholds, electrode impedances, and psychophysical comfort levels, as well as speech perception results pre- and post-operatively and standardized evaluations of quality of life.

Methods: Forty-four subjects were implanted with the CI532. Electrically evoked compound action potential (ECAP) thresholds and impedances were measured using automatic Neural Response Telemetry intra-operatively, at activation and at six months post implant. Pre- and post-operative measures of words in quiet and sentences in noise were made in multiple languages. Quality of life was assessed using The Speech Spatial Qualities questionnaire (SSQ) and Glasgow Benefit Inventory (GBI).

Results: Intra-operative ECAP thresholds were recorded successfully from 90% of electrodes tested. ECAP thresholds varied across the array and a post-hoc Dunn’s test showed that median thresholds for electrodes E1–E13 were significantly greater than those for E17–E22 (all P?<?0.001). Impedances increased significantly between surgery and activation. Speech recognition scores for words in quiet and sentences in noise showed a significant improvement for the group at six months, when using the cochlear implant, compared with pre-operative performance (P?<?0.001). There was a significant increase compared to pre-operative ratings for all sections of the SSQ at six months post activation (P?<?0.001). The GBI gave scores significantly above zero for the ‘general’ subscale and total score.

Conclusion: Objective ECAP and impedance measures for this new electrode array were as expected and similar to results reported for other array types. Speech perception and quality of life improved significantly following implantation.

Trial registration: ClinicalTrials.gov identifier: NCT02392403.     

Use of the Phantom Electrode strategy to improve bass frequency perception for music listening in cochlear implant users

Abstract

Objectives

The Phantom Electrode strategy makes use of partial bipolar stimulation on the two most apical electrodes in an effort to extend the frequency range available to cochlear implant (CI) users. This study aimed to quantify the effect of the Phantom Electrode strategy on bass frequency perception in music listening in CI users.

Methods

Eleven adult Advanced Bionics users with the Fidelity 120 processing strategy and 16 adult normal hearing (NH) individuals participated in the study. All subjects completed the CI-multiple stimulus with hidden reference and anchor (MUSHRA), a test of an individual's ability to make discriminations in sound quality following the removal of bass frequency information. NH participants completed the CI-MUSHRA once, whereas CI users completed the task twice – once with their baseline clinical program and once with the Phantom Electrode strategy, in random order. CI users’ performance was assessed in comparison with NH performance.

Results

The Phantom Electrode strategy improved CI users performance on the CI-MUSHRA compared with Fidelity 120.

Discussion

Creation of a Phantom Electrode percept through partial bipolar stimulation of the two most apical electrodes appears to improve CI users’ perception of bass frequency information in music, contributing to greater accuracy in the ability to detect alterations in musical sound quality.

Conclusion

The Phantom Electrode processing strategy may enhance the experience of listening to music and thus acoustic stimuli more broadly by improving perception of bass frequencies, through direction of current towards the apical portion of the cochlea beyond the termination of the electrode.     

Effects of cochlear implant surgical technique on post-operative electrode impedance

Conclusions: The mCI surgical technique led to reduced impedance and minimized disturbance of the microenvironment inside the cochlea. Atraumatic surgical techniques and inflammation-reduction strategies may preserve the cochlear architecture and prevent fibrotic development. Objectives: To assess the advantages of a modified minimal access technique in cochlear implantation as well as to investigate the effects of intra-operative application of inflammation reduction strategies on the intra-cochlear impedance. Methods: One hundred patients received a 31.5?mm long Med-El standard electrode array fully inserted into the cochlea and did not have surgical complications post-operation. Patients were divided into two groups according to the surgical technique that was used for implantation: 50 were in the modified minimal access cochlear implant (mCI) surgery group and 50 were in the traditional CI surgery group. Intra-cochlear impedance values were measured at initial activation (4 weeks post-operatively). Electrode impedance values were compared between the surgery groups. Results: Electrode impedance values were significantly lower in the mCI group than in the CI surgery group at initial activation (5.01 kOhm vs 6.10 kOhm, respectively, F?=?13.761, p?=?0.000). The differences between the two groups were most prominent for the electrodes located at the basal region of the cochlea.     

Novel method of fitting of children with auditory brainstem implants

ObjectivesTo develop a reliable and objective fitting method for use with young children with an auditory brainstem implant (ABI).Materials and methodsSubjects were 17 young children implanted with an ABI with the mean age 2 years and 4 months (8–64 months). Evoked auditory brainstem response (eABR) measurements were performed intraoperatively and at activation in order to record the auditory response and non-auditory side effects. Each child was tested to observe any subjective responses to the electric stimuli and non-auditory side effects. All children were fitted based on the postoperative eABR. The minimum follow up time was 12 months.ResultsIntraoperatively an eABR could be obtained in all children. The responses were recordable from 75–100% of all electrodes. At initial stimulation eABR were recordable in all children. The eABR was obtained in 79.7% of all electrodes (25–100%) with a mean eABR threshold of 22.3 nC. eABR without any non-auditory stimulation was recorded on all electrodes in 11 children. Mixed eABR and non-auditory responses were recorded on 2–6 electrodes in 6 children. The subjective auditory responses for at least 1 electrode were noted in 15 children. In the 2 remaining cases the auditory response was obtained only when the device was activated. In all children the subjective responses were within the estimated dynamic range for each electrode. Each child was able to accept up to 100% of volume of the created map. The non-auditory response was observed only on children and electrodes with mixed eABR and non-auditory responses. The mean CAP score at 6 months after the activation was 2.4 (1–4).ConclusionseABR seems to be a reliable tool to judge ABI electrode placement and a reliable method for fitting of young children with an ABI. The data suggest that eABR-based fitting helps children to more quickly achieve auditory perception and development.     

Feasibility of hearing preservation for residual hearing with longer cochlear implant electrodes

Abstract

Background: Hearing preservation is thought to be achievable following atraumatic surgery with thin cochlear implant electrodes; therefore, the surgical approach and implant electrode design are crucial considerations.

Objective: To assess the feasibility of hearing preservation with long electrodes for patients meeting the criteria for conventional cochlear implantation.

Methods: One hundred and two patients (132 ears) who underwent cochlear implant surgery were analyzed. Inclusion criteria included measurable residual hearing in the low frequency before implantation and not meeting the criteria for electric acoustic stimulation (EAS).

Results: Of the 18 patients with residual hearing in the low frequency enrolled, 17 subjects (94.4%) retained low frequency hearing. A younger age at surgery tended to contribute to better hearing preservation than that observed in older patients. There was no clear trend regarding the influence of insertion depth angle of the electrode on hearing preservation.

Conclusion: It is possible to achieve hearing preservation in the lower frequency by the use of longer electrodes. This study underscores the importance of atraumatic surgery, even for patients with only limited residual hearing, and longer electrodes should be adopted for EAS.     

Large vestibular aqueduct syndrome: Impedance changes over time with different cochlear implant electrode arrays

Abstract

Objectives

The aim of this study was to assess if large vestibular aqueduct syndrome (LVAS), with the increase in perilymphatic pressure, affects impedance changes over time with different types of Cochlear^® implant electrode arrays Contour, Straight, and CI 422. To report speech perception outcomes for these cochlear implant recipients.

Methods

Retrospective case review of impedance levels and categories of auditory performance. Impedance data were collected at switch on, 1 month, 3, 6, 12, and 24 months after cochlear implantation and compared with control (non-LVAS cochlear implant recipient) data for each array type. Forty-seven patients with exclusive LVAS and no other vestibulocochlear abnormalities or other identifiable cause of deafness were eligible for inclusion in the study.

Results

In LVAS patients, there was a significant difference in impedance between the three types of device (P < 0.0001). Time since switch on was associated with a decrease in impedance for all three devices (P < 0.0001). The mean impedance reduced between switch on and 1 month and remained relatively constant thereafter. Sound variation with softening of sounds was seen in four CI 422 (Straight Research Array) recipients due to ongoing fluctuations in electrode compliance.

Discussion

For all three array types, there was no significant difference in the mean impedance between the LVAS patients and controls over the first 12 months. In keeping with previous studies cochlear implant recipients with LVAS hear very well through the cochlear implant.     

Dynamic intracochlear pressure measurement during cochlear implant electrode insertion

Abstract

Background: Electrode insertion into the cochlea can cause significant pressure changes inside the cochlea with assumed effects on the cochlea’s functionality regarding residual hearing. Model-based intracochlear pressure (ICP) changes were performed statically at the cochlear helix.

Aims/objectives: The aim of this study was to observe dynamic pressure measurements during electrode insertion directly at the cochlear implant electrode.

Material and methods: The experiments were performed in an uncurled cochlear model that contained a volume value equivalent to a full cochlea. A microfibre pressure sensor was attached at one of two positions on a cochlear implant electrode and inserted under different insertional conditions.

Results: We observed the ICP increase depending on the insertional depth. A sensor-position-specific pressure change is insertional-depth dependent. Interval insertion did not lead to a lower peak insertional ICP.

Conclusions and significance: In contrast to the static pressure-sensor measurement in the artificial model’s helix, a dynamic measurement directly at the electrode shows the pressure profile to increase based on the insertional depth. A mechanical traumatic relevance of the observed pressure values cannot be fully excluded.     

多导人工耳蜗植入后电极阻抗的初步研究

目的研究多导人工耳蜗植入后电极阻抗变化的特点,对比直电极和弯电极的阻抗差异,为人工耳蜗植入术后的调试提供参考。方法在Nucleus多导人工耳蜗编程调试界面上,应用R126V1.3和NRTV3.0软件,测试11例语前聋儿童在不同时期的阻抗值,并进行分析比较。结果CI24M和CI24Rcontour两种植入体阻抗随时间变化的基本规律是:术中较低,开机时最高,以后随时间推移逐渐降低。CI24Rcontour阻抗高于CI24M。结论人工耳蜗植入体阻抗开机后随时间推移而逐渐降低,新型CI24Rcontour植入体与CI24M相比,其阻抗值在术中至开机后3周内明显要高。     

人工耳蜗植入术后电极阻抗特性分析

目的对使用人工耳蜗系统患者的电极阻抗数值进行分析,总结电极阻抗的变化规律,为临床制定合理的术后调试计划提供依据。方法对152位使用澳大利亚Cochlear Nucleus24M型人工耳蜗系统的患者于术后4周左右安装体外设备并进行测试,使用澳大利亚Cochlear公司提供的R116或R126软件进行电极阻抗测试。结果患者电极阻抗数值自术中至术后开机时呈显著增加的趋势,在开机时达到最大,其后随开机时间的增长显著降低,至开机3个月后趋于稳定,不同部位的电极显示了相同的变化趋势。结论电极阻抗数值随术后使用时间及电极部位的变化而变化。在开机3个月内需多次进行调试,从而为患者提供最适合的程序,使患者的言语感知达到最佳状态。     

Nucleus 24CA型人工耳蜗植入后电极阻抗及T/C值变化分析

目的观察Nucleus 24CA型人工耳蜗植入后电极阻抗、行为反应阈值(T-level,T级)及最大舒适级(C-level,C级)的变化规律,分析其内在联系,探讨其对术后调机的指导意义。方法对81例植入Nucleus 24CA型人工耳蜗患儿,分别在术中、术后1、2、6个月进行电极阻抗阈值测试,收集术后对应T、C值,并对其变化规律及相关性进行统计学分析。结果电极阻抗值术中检测最低,术后1月开机最高,此后逐渐减低(P<0.01);自蜗顶至蜗底各通道间电极阻抗值无显著差异(P>0.05)。各电极通道T值、C值随术后时间延长逐渐增高(P<0.05),并与电极阻抗值呈线性相关。结论测定电极阻抗值是评估人工耳蜗刺激电极状态的有效手段;术后2月应同时调试T值及C值,此后则应对C值进行重点调试。     

Electric-acoustic stimulation with longer electrodes for potential deterioration in low-frequency hearing

Abstract

Background: Electric-acoustic stimulation (EAS) has emerged as a standard treatment for patients with high-frequency hearing loss. EAS is usually performed with shorter electrodes of 16–24?mm in length. As most EAS recipients gradually lose residual acoustic hearing in the implanted ear over time, EAS with longer electrodes without causing significant intra-cochlear damage might be ideal.

Objective: The aim of this study was to investigate hearing preservation (HP) results after EAS surgery with longer electrodes.

Methods: Ten patients (11 ears) with partial deafness that met the indications for EAS with a MED-EL FLEX28 electrode were included in this study. Auditory thresholds before and at 6?months after activation were examined.

Results: In 100% of cases, HP was comfortably achieved, indicating that all patients could utilize acoustic amplification combined with electric stimulation.

Conclusion: EAS with longer electrodes can offer broader cochlear coverage, resulting in natural frequency matching in comparison with shorter electrodes, even in EAS cases. The combination of advanced surgical techniques and flexible, long, straight electrodes permits deep insertion that reaches the apical region with little or no insertion trauma.     

Impact of cochlear tonotopy on electrically evoked compound action potentials (ECAPs)

Background: A wide range of cochlear implant electrode designs exists. Lateral wall electrodes may be favored for their potential to preserve residual hearing by virtue of being thin and delicate; whereas perimodiolar electrodes may have advantages in case of profound hearing loss, due to electrode positioning in close proximity to the auditory nerve fibers.

Aim: The aim of this study was to investigate the impact of these two array designs on the interaction between electrodes and the auditory nerve in different tonotopic regions of the cochlea.

Patients and methods: A retrospective study of both adult and pediatric cochlear implant recipients (CI24RE/CI512 or CI422, Cochlear®) was undertaken. The differences of threshold Neural Response Telemetry (tNRT) acquired 12 months after surgery were analyzed with respect to the tonotopic location.

Results: The results of 168 implants showed that perimodiolar arrays had lowest thresholds in the basal region whereas straight arrays had lowest thresholds in the apex. Highest thresholds for both array types were encountered in the medial parts.

Conclusions and Significance: tNRTs differ depending on electrode type and location inside the cochlea. This should be considered pre implantation when choosing the electrode array type and post-implantation when mapping the CI program.