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.     

术中圆窗耳蜗电图对人工耳蜗植入电极安全性评估

目的：分析人工耳蜗电极植入前后圆窗耳蜗电图（R W EcochG）中耳蜗微音电位（CM）阈值的变化,以客观评估人工耳蜗植入手术是否对耳蜗基底膜造成损伤。方法：对40例拟行人工耳蜗植入术的患者在全身麻醉下行R W EcochG测试,分析植入电极前后CM阈值的变化。结果：40例人工耳蜗植入患者中,39例电极植入前后CM阈值相近,且在个别频率植入电极后CM阈值减小5dB;仅有1例患者电极植入后CM阈值比植入前明显增加,术中植入电极时有阻力感。结论：术中RWEcochG测试可以客观评估人工耳蜗植入手术本身是否对耳蜗基底膜造成损伤。     

Intra- and postoperative electrode impedance of the straight and Contour arrays of the Nucleus 24 cochlear implant: relation to T and C levels

The objective of this study was to investigate electrode impedance in cochlear implant recipients in relation to electrically evoked stapedius reflex measurements during surgery, and to electrode design, stimulation mode, and T and C levels over a nine month period after surgery. Seventy-five implant recipients, implanted with a Nucleus straight electrode array or a Contour array, were included. The results show that: (1) during surgery electrode impedance decreases markedly after electrically evoked stapedius reflex measurements, (2) after surgery, during the period without stimulation until speech processor switch-on, impedance increases, (3) after processor switch-on impedance decreases. The lower impedance values after a period of stimulation are found at the higher T and C levels. Impedances of the straight array electrodes are lower than those of the Contour array. The difference corresponds mainly to their respective surface areas. In addition, the straight array shows a larger increase of impedance in the apical direction than the Contour array, probably because of the larger fluid environment around the basal electrodes of the straight array.     

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。     

Reference function of old electrical stimulation electrode in cochlear-reimplantation in children

ObjectivesTo explore the causes of cochlear implantation and reference function of old electrical stimulation electrode in cochlear reimplantation in children.MethodsThe causes, surgical methods and problems found during the operations of 24 cases of cochlear reimplantation in Henan Children's Hospital from June 2016 to April 2018 were analyzed.ResultsTwenty-three cases successfully completed the surgery of cochlear-reimplantation, and the remaining one case had approximately 1/3 of the anterior end of the residual cochlear electrode due to high resistance at the time of withdrawal of the electrodes. The causes of re-implantation were implant equipment failure (eleven cases), elevated impedance values of all electrodes after head trauma (two cases), and implant prolapse together with the electrode caused by a traffic accident (one case).ConclusionThe old stimulus electrode can provide an important reference to reduce the risk of operation and ensure the success of the reoperation.     

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.     

368例人工耳蜗植入手术分析

目的探讨人工耳蜗植入手术的操作程序,以提高手术效率及手术安全性。方法回顾性分析人工耳蜗植入手术368例,手术均采用经后鼓室径路。术中行电极阻抗测试和神经反应遥测,术后拍耳蜗位X线平片判断电极植入情况,术后一个月开机调试及跟踪随访。结果所有患者电极全部顺利植入,人工耳蜗装置工作状态正常。术后3天1例出现迟发型面瘫,用激素保守治疗后逐渐恢复,术后45天1例患儿发生外耳道炎,术后2个月1例出现乳突及耳后骨膜下脓肿,术后7个月1例由于头部外伤致植入体损坏更换植入体,经积极处理后均恢复良好。全部病例术后随访24个月无永久性面瘫、植入体移位及脑膜炎等严重并发症发生,但术后4年3例患儿出现植入体外露合并皮肤感染。结论熟练掌握手术技巧并根据个体特点进行人工耳蜗植入手术对于提高植入成功率、重建听觉、减少手术并发症有着非常重要的意义,术后的长期随访甚至终生随访是必要的。     

Imaging of electrode position in relation to electrode functioning after cochlear implantation

This study assessed the electrode position in cochlear implant patients and evaluated the extent to which the electrode position is determinative in the electrophysiological functioning of the cochlear implant system. Five consecutively implanted adult patients received a multichannel cochlear implant. In all patients, the electrical impedance and the electrically evoked compound action potentials were recorded immediately after implantation. Multislice computer tomography was performed 6 weeks postoperatively before switch-on of the cochlear implant. The electrode position relative to the modiolus was assessed and correlated to the electrophysiological measurements. All electrodes were fully inserted; this was confirmed by computer tomography. The individual electrode distance toward the modiolus could be most precisely analyzed for the basal part of the electrode array. It was thus decided to study the data of electrodes one, four, and seven. No correlation was found between electrical impedance and electrode distance. A significant correlation was found between electrode distance and the electrically evoked compound action potentials, with a 96% probability using Kendall’s rank correlation. We conclude that the electrode–modiolus distance is of importance to the stimulation of auditory nerve fibers. Future developments in imaging will further improve and refine our insight in the relation between electrode positioning.     

儿童人工耳蜗植入术后电诱发复合动作电位分析

目的 应用神经反应遥测(NRT)技术,观察人工耳蜗植入后不同时间段的电诱发复合动作电位(ECAP)阈值变化,探讨其对人工耳蜗术后调机的指导意义。方法 对33例使用Nucleus CI24R(CA)型人工耳蜗植入的患儿,于术中及术后1、1.5、2、4、6个月进行ECAP 阈值测试,统计分析其变化规律。结果 33例165个电极的波形检出率为93.3%。电极1、7、11、17、22的术中ECAP阈值与术后30d开机时的ECAP阈值的差异有统计学意义。同一测试电极,随术后开机时间的增长,ECAP阈值呈逐渐增加的趋势。经单因素方差分析,术后不同测试时间ECAP阈值差异有统计学意义。结论 ECAP检出率高,术中可用于检测神经反应;术后可协助估算患者的行为反应T、C级,指导调机,尤其对儿童患者更为重要。     

Our experience with split electrode array implant for obliterated cochlea

To study the outcomes of split electrode array cochlear implantation in ossified cochlea using the CAP scoring system. Retrospective case study. Tertiary referral center. Six cochleae in three adult and three pediatric patients with ossification. Intervention(s): All Patients underwent cochlear implantation with a split electrode array system. Major outcome parameter(s): Number of electrodes inserted during surgery, number of functioning electrodes on follow-up and auditory performance evaluation using the CAP score-Category of Auditory Perception [TSC Revised Version, based on Nottingham CI Program, 1995]. Six patients (three children and three adults) had insertion of split electrode array system. The mean number of electrodes inserted were 18.3 (range 15-21) and functioning electrodes at follow-up were mean of 14.3 (range 7-21). Auditory performance was measured using CAP score at 1?year post implant follow up, mean score in children was six and that in adult was eight. One pt had facial nerve twitching which was corrected by switching off the concerned electrode. No complications in sort of facial palsy or vestibular disorder were observed. Patients of ossified cochlea having profound deafness do well with split electrode array cochlear implantation as evaluated with CAP scoring system. The split electrode array results in more number of electrodes within the cochlear lumen. Retro graded apical array insertion has less chances of facial nerve stimulation as it is placed away from the nerve.     

Long-term measures of electrode impedance and auditory thresholds for the Ineraid cochlear implant.

Measures of electrode impedance and of detection thresholds for electrical stimuli were extracted from the records of patients implanted with the Ineraid cochlear prosthesis. An analysis of impedance measures, obtained at 1, 12, 24, and 36 months after surgery, demonstrated (a) a significant decrease in impedance over the first year for electrodes that carried current and (b) significant increases in impedance at 24 and 36 months for electrodes that did not carry current. An analysis of detection thresholds, obtained at the same times as the impedance measures, demonstrated that averaged thresholds for the current-carrying electrodes varied no more than 0.5 dB over the 3-year period. These results support the conclusion that stimulation with the Ineraid device does not produce deleterious changes in the electrodes or in the target neural tissue.     

Effects of round window dexamethasone on residual hearing in a Guinea pig model of cochlear implantation

To study electric acoustic stimulation, we have developed a model of guinea pig cochlear implantation via a cochleostomy. Thirty minutes prior to implantation, a hyaluronic acid/carboxymethylcellulose bead, loaded with either dexamethasone or normal saline, was placed upon the round window membrane. Animals that did not receive beads acted as controls. Pure-tone auditory brainstem response thresholds were estimated before and after electrode insertion, and 1 and 4 weeks later. Selected cochlear histology was performed. RESULTS: Dexamethasone could be detected in the cochlea for 24 h after cochlear implantation. Thresholds were elevated across frequencies in all animals immediately after surgery. These thresholds recovered completely at and below 2 kHz, and partially at higher frequencies by 1 week after implantation. At 32 kHz, but not the lower frequencies, the presence of dexamethasone had a significant protective effect upon hearing, which increased in magnitude over time. The protection was greatest in difficult implantations where an intractable resistance to electrode insertion was met. There was a persistent foreign body reaction at the site of implantation of saline-treated implanted ears but not in the dexamethasone-treated implanted ears. CONCLUSION: Short-term preoperative delivery of dexamethasone through the round window can protect residual hearing during cochlear implantation, especially during technically difficult surgery.     

Toward a battery of behavioral and objective measures to achieve optimal cochlear implant stimulation levels in children

OBJECTIVES: Children require audible and comfortable stimulation from their cochlear implants immediately after device activation. To accomplish this, a battery of objective measures may be needed that could include the electrically evoked stapedius reflex (ESR), compound action potential from the auditory nerve (ECAP), and/or auditory brain stem response (EABR). In the present study, the following specific research questions were asked: In children using cochlear implants, 1) Can the ECAP, EABR, and ESR be recorded at the time of cochlear implantation? 2) What is the feasibility of measuring the ECAP, EABR, and the ESR repeatedly without the use of sedation over the first year of implant use? 3) Do ECAP, EABR, and ESR thresholds or behavioral measures change over time? 4) What is the relation between ECAP, EABR, and ESR thresholds and behavioral measures of threshold and comfortably loud levels? DESIGN: In 68 children, ECAP, EABR, and ESR responses as well as behavioral measures of stimulation threshold and maximum stimulation were recorded at regular intervals over the first year of implant use. In each child, responses were recorded to electrical pulses provided by three different electrodes along the implanted array. Visual inspections of the stapedius reflex (V-ESR) evoked by activation of the same three electrodes at the time of surgery were performed in an additional 20 children. RESULTS: ECAP and EABR measures were obtained in more than 84% of electrodes tested and 89% of children tested both in the operating room at the time of implant surgery (OR) and after surgery in nonsedated children. ESRs were recorded by using immittance measures in more than 65% of electrodes tested and 67% of children tested by 3 mo of implant use, but this technique was less successful in the OR and during early stages of device use. V-ESRs and ECAP thresholds were higher in the OR than ESRs and ECAPs at postoperative recording times. EABR and ECAP thresholds did not significantly change over the first 6 and 12 mo of implant use, respectively, whereas ESR thresholds increased. Behavioral measures of threshold decreased over time, whereas maximum stimulation levels rose over time. Behavioral measures of threshold and loudness were highly correlated at all test times. ECAP, EABR, and behavioral measures were lower when evoked by an electrode at the apical end of the implanted array than by more basal electrodes. Behavioral thresholds could be predicted mainly by ECAP thresholds, whereas maximum stimulation levels could best be predicted by ESR thresholds; both were significantly affected by the age at implantation. CONCLUSIONS: A combination of nonbehavioral measures can aid in the determination of useful cochlear implant stimulation levels, particularly in young children and infants with limited auditory experience. These measures can be made in the operating room and can be repeated after surgery when needed. Correction factors to predict threshold stimulation levels should be based on ECAP thresholds or EABR thresholds if necessary. Correction factors should be made for at least one apical and mid-array electrode, should take into account the age of the child, and may have to be revised during the first year of implant use. Maximum stimulation levels may be best determined by using the ESR.     

Feasibility of one-day activation in cochlear implant recipients

Objective: To determine if cochlear implants recipients can be safely and effectively fitted with their sound processor one day after their implant surgery. Design: All subjects were implanted with MED-EL Concerto cochlear implant. Subjects’ electrode impedance levels, maximum comfortable levels, and threshold levels were measured one day after surgery and compared to measurements obtained one month post implantation using the non-parametric Wilcoxon signed-rank test. Study sample: Twenty-nine participants in the age range of 1 to 42 years (average of 5 years). Results: No adverse events were reported post-operatively. Measures after one day of surgery were significantly less than those measured one month post implantation. Conclusion: Early activation of the implant did not impact the healing process of the incision site, suggesting that one-day activation of the implant is feasible for some patients when medically possible. The evolution of the impedance and stimulation levels were consistent with that reported in previous studies, which indicates that early activation did not interfere with the physiological changes taking place after implantation.     

Electrocochleography in cochlear implantation: Development,applications, and future directions

Electrocochleography (ECochG) is an electrophysiological technique that records electrical potentials generated by different components of the inner ear and peripheral cochlear nerve in response to acoustic stimulation. ECochG responses can be analyzed into (1) cochlear microphonics (CM), (2) auditory nerve neurophonics, (3) summating potential, and (4) compound action potential. Over the past few decades, there have been ongoing refinements in technique and updates in the understanding of recorded potentials. Historically, ECochG found its main application in the diagnostic evaluation of Meniere’s disease (MD). However, in the last decade, the focus has shifted towards cochlear implantation (CI). In patients with residual hearing after CI, combined electric and acoustic stimulation has resulted in improved hearing and speech outcomes. Despite efforts to mitigate trauma during electrode insertion, hearing preservation rates vary after surgery. During implantation, real-time ECochG offers an opportunity to measure frequency specific CMs elicited from a localized region in the cochlea as the surgeon inserts the electrode array. In extracochlear ECochG recordings, the recording electrode can be placed on the promontory, the stapes, or the tympanic membrane. Intracochlear ECochG can be performed by inserting a recording electrode into the cochlea or by using one of the CI electrodes as the recording electrode. The loss of intraoperative ECochG signal may indicate cochlear trauma from electrode insertion, but the association between intraoperative ECochG changes and cochlear trauma remains controversial. The ability to monitor cochlear trauma during CI electrode placement holds promise to improve hearing preservation outcomes, modify surgical techniques, and change electrode design. The goal of this review is to provide a comprehensive overview of the electrophysiology and history of ECochG, discuss its recent applications in CI, and explore the ongoing research in this expanding field.     

The Nucleus Double Array Cochlear Implant: a new concept in obliterated cochlea]

AIM: In order to increase the number of intracochlear electrodes to be inserted into a totally obliterated cochlea a special implant has been developed in collaboration with Cochlear Ltd. The implant features two separate electrode carriers containing 11 and 10 active electrodes, respectively, and a reference electrode on the receiver stimulator package. The potential stimulation modes include monopolar and bipolar stimulation as well as stimulation between both arrays. SURGICAL TECHNIQUE: A cochleostomy at the round window provides access to the scala tympani. Newly formed bone is removed as far as the anterior portion of the basal turn. Care is taken to identify and preserve the osseous border of the cochlea. A second cochleostomy is performed immediately caudal to the cochleariform process after removal of the incus. New tissue can be removed here in the same way. The two electrode carriers are then placed into the first and the second turn respectively. The remaining procedure corresponds to the procedure for cochlear implantation in cases in which the cochlea is not obliterated. PATIENTS: For the purpose of a clinical study n = 10 patients aged between 32-66 years with an obliterated cochlea were fitted with a double array cochlear implant. All patients showed signs of total obliteration of the basal turn either in preoperative imaging or during surgery. Intraoperative inspection revealed that the second turn was not obliterated in 4 of 10 patients. POSTOPERATIVE RESULTS: Postoperatively, a standard test battery was used to determine auditory performance over a period of time. All patients achieved significantly better speech understanding due to the additional apical electrode array. No complications occurred. CONCLUSION: In cases involving an obliterated cochlea, the number of intracochlear electrodes can be increased with the double array implant. As a result, the patients achieve significantly better auditory results.     

Electrode impedance changes over time in MED El cochlear implant children recipients: Relation to stimulation levels and behavioral measures

Objective: Electrode impedance measures resistance encountered by electric current passing through wires, electrodes and biological tissue. This study was designed mainly to evaluate changes in electrode impedance values and psycho-electric parameters changes (i.e. threshold levels, comfortable levels, and dynamic range) in cochlear implant patients over time.

Methods: It was a prospective study encompassing 20 patients implanted by MED-EL device programd using behavioral programs. Electrical stimulation levels and electrode impedance values were examined at 0, 1, 3 and 6 months after the first fitting session.

Results: Electrode impedance values were reduced from the time of activation to the 6 months visit. Most comfortable levels increased and dynamic range widened until the 6 months visit. There was an inverse correlation between impedance values and most comfortable level as well as dynamic range, over time.

Conclusion: Frequent monitoring of electrode impedance (for device and electrodes problems) and electric stimulation levels (for better performance, mapping and habituation) during the first 6 months of implant use is recommended.     

Mondini畸形多道人工耳蜗植入的效果分析

OBJECTIVE: To describe clinical experiences with multi-channel cochlear implantation in patients with Mondini malformation. METHODS: Among 300 patients who received multi-channel cochlear implants from 1996 to 2002 in Beijing Tongren Hospital, 15 patients were diagnosed with Mondini malformation. A retrospective analysis was performed dealing with the surgical techniques, mapping and rehabilitations characteristics after surgery. 15 patients with normal cochlear structure are consider as control group. RESULTS: Gusher is found more common than the normal cochlear implantation, most of them are serious. The electrodes are inserted in the "cochleostomy" in full length of 13 Patients, 2 pairs of electrodes remains outside of "cochleostomy" in 2 patients. No serious complications occurred after implantation. All patients have auditory sensations. The impedance of the electrodes, the T level, C level and the hearing threshold are similar with the normal cochlear implantation group. The results have no significant difference in compare with normal cochlear group(P > 0.05). CONCLUSION: Multi-channel cochlear implantation could be performed safely in patients with Mondini malformation. The primary outcome for patients with Mondini malformation are similar to those with normal cochlear structure following the multi-channel cochlear implantation.     

Cochlear pathology following chronic electrical stimulation of the auditory nerve. I: Normal hearing kittens.

The present study examines the histopathological effects of long-term intracochlear electrical stimulation in young normal hearing animals. Eight-week old kittens were implanted with scala tympani electrode arrays and stimulated for periods of up to 1500 h using charge balanced biphasic current pulses at charge densities in the range 21-52 microC cm-2 geom. per phase. Both click and electrically evoked auditory brainstem responses were periodically recorded to monitor the status of the hair cell and spiral ganglion cell populations. In addition, the impedance of the stimulating electrodes was measured daily to monitor their electrical characteristics during chronic implantation. Histopathological examination of the cochleas showed no evidence of stimulus induced damage to cochlear structures when compared with implanted, unstimulated control cochleas. Indeed, there was no statistically significant difference in the ganglion cell density adjacent to the stimulating electrodes when compared with a similar population in implanted control cochleas. In addition, hair cell loss, which was restricted to regions adjacent to the electrode array, was not influenced by the degree of electrical stimulation. These histopathological findings were consistent with the evoked potential recordings. Finally, electrode impedance data correlated well with the degree of tissue growth observed within the scala tympani. The present findings indicate that the young mammalian cochlea is no more susceptible to cochlear pathology following chronic implantation and electrical stimulation than is the adult.     

耳蜗骨化与人工耳蜗植入

目的 探讨耳蜗骨化状态下人工耳蜗植入手术的经验及分析术后效果.方法 北京同仁医院自1996年开展多道人工耳蜗植入手术以来,截止到2006年12月已开展手术600余例,遇到双侧耳蜗骨化患者7例.其中4例有明确的脑膜炎病史,3例耳蜗骨化原因不明.3例为耳蜗完全骨化;1例鼓阶完全骨化,前庭阶未受累;1例耳蜗部分骨化;2例耳蜗部分纤维化.总结术前、术中及术后的处理原则、方法及术后康复效果.结果 1例术中出现镫井喷,但比其他内耳畸形术中出现镫井喷的程度轻微;4例电极完全插入耳蜗内,2例植入部分电极,1例家属放弃植入;术后无面神经麻痹、脑脊液瘘等并发症;术后开机调试发现部分患者T值、C值比正常形态耳蜗植入偏高(因病例数量少未做统计学分析),但听阈无明显区别.术后语训听力及言语能力均有不同程度的提高.结论 对于耳蜗部分骨化患者,术中只要将其骨化成分自鼓阶内清除后可顺利植入电极;对于完全骨化患者可以将围绕蜗轴的鼓阶顶壁钻开,将电极嵌入骨槽内即可.脑膜炎后出现重度感音性聋应考虑耳蜗骨化的可能,常规颞骨CT及MRI检查,一旦确诊应尽快手术,以免耳蜗完全骨化.人工耳蜗植入术可以作为伴有耳蜗骨化的深度感音性聋患者的治疗和康复手段.