Evoked Compound Action Potential Thresholds Research Articles

First evidence of a biomarker-based dose-response relationship in chronic pain using physiological closed-loop spinal cord stimulation

Background and objectivesIn spinal cord stimulation (SCS) therapy, electricity is the medication delivered to the spinal cord for pain relief. In contrast to conventional medication where dose is determined by...

Evoked compound action potentials during spinal cord stimulation: effects of posture and pulse width on signal features and neural activation within the spinal cord

Objective. Evoked compound action potential (ECAP) recordings have emerged as a quantitative measure of the neural response during spinal cord stimulation (SCS) to treat pain. However, utilization of ECAP recordings to optimize stimulation efficacy requires an understanding of the factors influencing these recordings and their relationship to the underlying neural activation. Approach. We acquired a library of ECAP recordings from 56 patients over a wide assortment of postures and stimulation parameters, and then processed these signals to quantify several aspects of these recordings (e.g., ECAP threshold (ET), amplitude, latency, growth rate). We compared our experimental findings against a computational model that examined the effect of variable distances between the spinal cord and the SCS electrodes. Main results. Postural shifts strongly influenced the experimental ECAP recordings, with a 65.7% lower ET and 178.5% higher growth rate when supine versus seated. The computational model exhibited similar trends, with a 71.9% lower ET and 231.5% higher growth rate for a 2.0 mm cerebrospinal fluid (CSF) layer (representing a supine posture) versus a 4.4 mm CSF layer (representing a prone posture). Furthermore, the computational model demonstrated that constant ECAP amplitudes may not equate to a constant degree of neural activation. Significance. These results demonstrate large variability across all ECAP metrics and the inability of a constant ECAP amplitude to provide constant neural activation. These results are critical to improve the delivery, efficacy, and robustness of clinical SCS technologies utilizing these ECAP recordings to provide closed-loop stimulation.

Relationship between electrically evoked compound action potential thresholds and behavioral T-levels in implanted children with cochlear nerve deficiency

It is challenging to program children with cochlear nerve deficiency (CND) due to limited auditory and speech abilities or concurrent neurological deficits. Electrically evoked compound action potential (ECAP) thresholds have been widely used by many audiologists to help cochlear implant programming for children who cannot cooperate with behavioral testing. However, the relationship between ECAP thresholds and behavioral levels of cochlear nerve in children with CND remains unclear. This study aimed to investigate how well ECAP thresholds are related to behavioral thresholds in the MAP for children with CND. This study included 29 children with CND who underwent cochlear implantation. For each participant, ECAP thresholds and behavioral T-levels were measured at three electrode locations across the electrode array post-activation. The relationship between ECAP thresholds and behavioral T-levels was analyzed using Pearson’s correlation coefficient. The results showed that ECAP thresholds were significantly correlated with behavioral T-levels at the basal, middle, and apical electrodes. ECAP thresholds were equal to or higher than the behavioral T-levels for all tested electrodes, and fell within MAP’s dynamic range for approximately 90% of the tested electrodes. Moreover, the contour of the ECAP thresholds was similar to the contour of T-levels across electrodes for most participants. ECAP thresholds can help audiologists select stimulation levels more efficiently for children with CND who cannot provide sufficient behavioral response.

Single-incision cochlear implantation and hearing evaluation in piglets and minipigs

ObjectivesVarious animal models have been established and applied in hearing research. In the exploration of novel cochlear implant developments, mainly rodents have been used. Despite their important contribution to the understanding of auditory function, translation of experimental observations from rodents to humans is limited due to the size differences and genetic variability. Large animal models with better representation of the human cochlea are sparse. For this reason, we evaluated domestic piglets and Aachen minipigs for the suitability as a cochlear implantation animal model with commercially available cochlear implants. MethodsFour domestic piglets (two male and two female) and six Aachen minipigs were implanted with either MED-EL Flex24 or Flex20 cochlear implants respectively, after a step-by-step surgical approach was trained with pig cadavers. Electrophysiological measurements were performed before, during and after implantation for as long as 56 days after surgery. Auditory brainstem responses, electrocochleography as well as electrically and acoustically evoked compound action potentials were recorded. Selected cochleae were further analyzed histologically or with micro-CT imaging. ResultsA surgical approach was established using a retroauricular single incision. Baseline auditory thresholds were 27 ± 3 dB sound pressure level (SPL; auditory brainstem click responses, mean ± standard error of the mean) and ranged between 30 and 80 dB SPL in frequency-specific responses (0.5 – 32 kHz). Follow-up measurements revealed deafness within the first two weeks after surgery, but some animals partially recovered to a hearing threshold of 80 dB SPL in certain frequencies as well as in click responses. Electrically evoked compound action potential thresholds increased within the first week after surgery, which led to lower stimulation responses or increase of necessary charge input. Immune reactions and consecutive scalar fibrosis following implantation were confirmed with histological analysis of implanted cochleae and may result in increased impedances. A three-dimensional minipig micro-CT segmentation revealed cochlear volumetric data similar to human inner ear dimensions. ConclusionsThis study underlines the feasibility of cochlear implantation with clinically used cochlear implants in a large animal model with representative inner ear dimensions comparable to humans. To bridge the gap between small animal models and humans in translational research and to account for the structural and size differences, we recommend the minipig as a valuable animal model for hearing research. First insights into the induced trauma in minipigs after cochlear implant surgery and a partial hearing recovery present important data of the cochlear health changes in large animal cochleae.

Spinal Evoked Compound Action Potentials in Rats With Clinically Relevant Stimulation Modalities

ObjectivesRats are commonly used for translational pain and spinal cord stimulation (SCS) research. Although many SCS parameters are configured identically between rats and humans, stimulation amplitudes in rats are often programmed relative to visual motor threshold (vMT). Alternatively, amplitudes may be programmed relative to evoked compound action potential (ECAP) thresholds (ECAPTs), a sensed measure of neural activation. The objective of this study was to characterize ECAPTs, evoked compound muscle action potential thresholds (ECMAPTs), and vMTs with clinically relevant SCS modalities. Materials and MethodsWe implanted ten anesthetized rats with two quadripolar epidural SCS leads: one for stimulating in the lumbar spine, and another for sensing ECAPs in the thoracic spine. We then delivered two SCS paradigms to the rats. The first used 50-Hz SCS with 50-, 100-, 150-, and 200-μs pulse widths (PWs), whereas the second used a 50-Hz, 150-μs PW low-rate program (LRP) multiplexed to a 1200-Hz, 50-μs PW high-rate program (HRP). We increased SCS amplitudes up to the vMT in the first paradigm, and in the second, we increased HRP amplitudes up to the HRP ECAPT with a fixed amplitude (70% of the vMT) LRP. For each test case, we captured ECAPTs, ECMAPTs, and vMTs from each rat. ResultsvMTs were 3.0 ± 0.7 times greater than ECAPTs, with vMTs marginally (3.0 ± 3.6%) greater than ECMAPTs (mean ± SD) across all PWs with the first paradigm. With the second paradigm, we noted a negligible increase (3.6 ± 6.2%) on the LRP ECAP as HRP amplitudes were increased. ConclusionsOur results demonstrate reasonable levels of neural activation in anesthetized rats with SCS amplitudes appropriately programmed relative to vMT or ECMAPT when using clinically relevant SCS modalities. Furthermore, we demonstrate the feasibility of ECAP recording in rats with multiplexed HRP SCS.

A Prospective Multicenter Case Series Utilizing Intraoperative Neuromonitoring With Evoked Compound Action Potentials to Confirm Spinal Cord Stimulation Lead Placement

ObjectivesThe use of intraoperative neuromonitoring (IONM) has been adapted to address issues of safety and proper lead positioning in spinal cord stimulation. This multicenter case series seeks to incorporate the use of evoked compound action potential (ECAP) and late response (LR) recording and compare it with the results obtained with IONM, specifically electromyography (EMG), for the confirmation of lead placement. This study aimed to establish a correlation between ECAPs, LR, and EMG and publish human recordings of ECAPs and LR during their use with IONM. Materials and MethodsStandard neuromonitoring protocols were followed at two institutions, with two separate physicians and with seven patients, as part of a larger ongoing study registered with ClinicalTrials.gov (NCT02924129). Stimulation and recording were performed, top and bottom, on each percutaneous lead. Stimulation amplitude was increased considering ECAP, LR, and EMG thresholds. ResultsECAPs, LRs, and EMG signals were observed in all patients. The onset of LR signals on implanted electrodes and EMG signal on subdermal electrodes was well correlated (rs = 0.94, p < 0.001), with a median LR:EMG value of 1.06 (N = 21). LR:EMG for the top (mean = 0.97, N = 8) vs bottom (mean = 1.15, N = 13) of the lead was compared using a paired Wilcoxon signed rank test and an independent samples Mann-Whitney test, revealing a marginally significant and a statistically significant difference (p = 0.078 and p = 0.015, respectively). Mean LR:ECAP was >2 in all locations and approximately 3.5 overall. LR:ECAP between the top and bottom of the lead was significantly different (Wilcoxon test, p < 0.01, N = 12). ConclusionsLR correlated with EMG; leads with bilateral (not necessarily symmetric) EMG activity showed LR:ECAP > 1.5. An LR:ECAP of <1, with LR/EMG generated before the ECAP, indicated that the lead is too lateral. The use of ECAP and LR has the potential of maintaining objective lead placement, without the need for needle placement with IONM.

The Evoked Compound Action Potential as a Predictor for Perception in Chronic Pain Patients: Tools for Automatic Spinal Cord Stimulator Programming and Control.

ObjectivesSpinal cord stimulation (SCS) is a drug free treatment for chronic pain. Recent technological advances have enabled sensing of the evoked compound action potential (ECAP), a biopotential that represents neural activity elicited from SCS. The amplitudes of many SCS paradigms – both sub- and supra-threshold – are programmed relative to the patient’s perception of SCS. The objective of this study, then, is to elucidate relationships between the ECAP and perception thresholds across posture and SCS pulse width. These relationships may be used for the automatic control and perceptually referenced programming of SCS systems.MethodsECAPs were acquired from 14 subjects across a range of postures and pulse widths with swept amplitude stimulation. Perception (PT) and discomfort (DT) thresholds were recorded. A stimulation artifact reduction scheme was employed, and growth curves were constructed from the sweeps. An estimate of the ECAP threshold (ET), was calculated from the growth curves using a novel approach. Relationships between ET, PT, and DT were assessed.ResultsETs were estimated from 112 separate growth curves. For the postures and pulse widths assessed, the ET tightly correlated with both PT (r = 0.93; p < 0.0001) and DT (r = 0.93; p < 0.0001). The median accuracy of ET as a predictor for PT across both posture and pulse width was 0.5 dB. Intra-subject, ECAP amplitudes at DT varied up to threefold across posture.ConclusionWe provide evidence that the ET varies across both different positions and varying pulse widths and suggest that this variance may be the result of postural dependence of the recording electrode-tissue spacing. ET-informed SCS holds promise as a tool for SCS parameter configuration and may offer more accuracy over alternative approaches for neural and perceptual control in closed loop SCS systems.

Short-Term Experience in Cochlear Implantation with Slim Modiolar Electrode Array (CI532): Comparison to Previous Devices

Background and Objectives There have been no reports in Korea regarding cochlear implant surgeries using Cochlear Nucleus Profile Slim Modiolar electrode [CI532 (Cochlear Ltd.)], as it has been recently released in Korea. We aimed to investigate the short-term results of CI532 and compare them with previous devices with perimodiolar or straight electrodes arrays from the same manufacturer.Subjects and Method From August 2018 to July 2019, 52 patients (26 adults; 26 children) who underwent cochlear implantation of CI532 were included. The intraoperative impedance and evoked compound action potential (ECAP) threshold in each electrode were analyzed and compared with the devices with a perimodiolar electrode array [Contour Advance&lt;sup&gt;®&lt;/sup&gt; (Cochlear Ltd.)] and a lateral wall electrode array [CI422 and CI522 (Cochlear Ltd.)]. Postoperative changes of hearing thresholds at each frequency (250, 500, and 1000 Hz) and aided word recognition scores (WRS) were also compared.Results CI532 showed significantly lower intraoperative impedance in the basal regions compared to the lateral wall electrode array. The ECAP thresholds of CI532 in the apical electrodes were significantly lower than that in the other two groups. After implantation, CI532 showed a significant preservation of hearing thresholds at most frequencies and showed significantly higher preservation rates than the other electrodes. However, there was no difference between the three groups regarding the postoperative short-term aided WRS.Conclusion CI532 showed lower intraoperative impedances and ECAP thresholds, and better short-term hearing preservation outcomes compared to the other electrodes, suggesting that CI532 electrode might be a better option with less traumatic insertion. However, there was no significant difference in the aided WRS, and further studies with a longer follow-up are necessary to examine the difference of audiologic outcomes.

Effect of Electrode to Modiolus Distance on Electrophysiological and Psychophysical Parameters in CI Patients With Perimodiolar and Lateral Electrode Arrays.

To investigate the intracochlear position of the latest Cochlear Nucleus 532 electrode array compared with the straight Nucleus 522 and the precurved 512 arrays and determine the effect of the electrode-modiolus distance on electrically evoked compound action potential, C-levels, electrically evoked stapedius reflex thresholds (ESRTs), and impedances. Postoperative high-resolution cone beam computational tomography images of 30 patients with Cochlear Nucleus 532, 522, and 512 implants were evaluated using the Comet (Cochlea Measurement Tool) program to determine the distance between the 22 individual electrode contacts and the medial wall. ESRTs were documented intraoperatively and electrophysiological as well as psychophysical parameters were measured at multiple time points including the first fitting after the initial activation. The electrode-modiolus distance in perimodiolar arrays is uniformly small across the array, whereas in a straight electrode carrier it varies significantly along the length of the array. Electrically evoked compound action potential thresholds and C-levels are larger with increased distance to the modiolus. Impedances and stapedius reflex thresholds do not differ significantly between the arrays. Our results show that the electrode position has a significant effect on both electrophysiological and psychophysical parameters, while impedances and ESRTs are not impacted. Novel tools can be used in the evaluation of high resolution cone beam computational tomography images to determine individual electrode-modiolus distances after cochlear implantation. The results of this study suggest that the correlations between electrode-modiolus distance and electrophysiological and psychophysical parameters are not sufficiently strong to adjust CI-fitting based on imaging data.

Comparison of Perimodiolar Electrodes: Imaging and Electrophysiological Outcomes.

The perimodiolar CI532 Slim Modiolar electrode has been designed to bring the electrode contacts close to auditory nerve while reducing cochlear trauma during its insertion. It is currently unknown to what extent the electrode position and electrophysiological outcomes of the Slim Modiolar electrode differ from other perimodiolar electrodes. The objective was to compare the electrode position and electrophysiological outcomes between the CI532 Slim Modiolar and CI512 Contour Advance electrode. Forty-six adult patients received a Slim Modiolar or Contour Advance electrode. Electrode types were compared using intraoperative electrode impedances, evoked compound action potential (ECAP) and stapedius reflex thresholds, as well as position parameters from postoperative computed tomography or digital volume tomography images (medial-lateral position, electrode-to-modiolus distance, insertion angle). The medial-lateral position indicates a closer modiolar placement of the Slim Modiolar compared with the Contour Advance. Individual electrode contact measurements, however, showed significantly larger electrode-to-modiolus distances and higher ECAP thresholds for the Slim Modiolar in the basal region. On contacts E20-22 the Slim Modiolar is slightly closer to the modiolus compared with the Contour Advance, but this did not result in lower ECAP thresholds. Perimodiolar electrodes can vary in their intracochlear position, leading to divergent electrophysiological outcomes. To detect these differences, investigations must be done for each electrode contact rather than using a global factor for the whole electrode array. While the electrode dislocation rate is lower with the Slim Modiolar than with the Contour Advance, electrode-to-modiolus proximity is smaller and ECAP thresholds are lower with the Contour Advance in the basal cochlear region.

Relationship Between Speech Recognition in Quiet and Noise and Fitting Parameters, Impedances and ECAP Thresholds in Adult Cochlear Implant Users.

The objective of this study was to identify parameters which are related to speech recognition in quiet and in noise of cochlear implant (CI) users. These parameters may be important to improve current fitting practices. Adult CI users who visited the Amsterdam UMC, location VUmc, for their annual follow-up between January 2015 and December 2017 were retrospectively identified. After applying inclusion criteria, the final study population consisted of 138 postlingually deaf adult Cochlear CI users. Prediction models were built with speech recognition in quiet and in noise as the outcome measures, and aided sound field thresholds, and parameters related to fitting (i.e., T and C levels, dynamic range [DR]), evoked compound action potential thresholds and impedances as the independent variables. A total of 33 parameters were considered. Separate analyses were performed for postlingually deafened CI users with late onset (LO) and CI users with early onset (EO) of severe hearing impairment. Speech recognition in quiet was not significantly different between the LO and EO groups. Speech recognition in noise was better for the LO group compared with the EO group. For CI users in the LO group, mean aided thresholds, mean electrical DR, and measures to express the impedance profile across the electrode array were identified as predictors of speech recognition in quiet and in noise. For CI users in the EO group, the mean T level appeared to be a significant predictor in the models for speech recognition in quiet and in noise, such that CI users with elevated T levels had worse speech recognition in quiet and in noise. Significant parameters related to speech recognition in quiet and in noise were identified: aided thresholds, electrical DR, T levels, and impedance profiles. The results of this study are consistent with previous study findings and may guide audiologists in their fitting practices to improve the performance of CI users. The best performance was found for CI users with aided thresholds around the target level of 25 dB HL, and an electrical DR between 40 and 60 CL. However, adjustments of T and/or C levels to obtain aided thresholds around the target level and the preferred DR may not always be acceptable for individual CI users. Finally, clinicians should pay attention to profiles of impedances other than a flat profile with mild variations.

The impact of auditory nerve functional states on the correlations between human and computer decisions for electrically evoked compound action potential threshold

ObjectivesThe electrically evoked compound action potential (ECAP) is widely used in clinical to reflect the functional states of the auditory nerve in cochlear implant (CI) recipients, especially in pediatric CI users. Currently, the software can automatically provide the ECAP threshold, which is convenient and not affected by the subjective judgement of the clinicians. However, it remains unclear whether the correlations between human and computer decisions for ECAP threshold can be affected by auditory nerve functional states, which is also the main purpose of our present study. MethodsIntracochlear electrical stimulation, which can decrease the excitability of the auditory nerve, was used to change the auditory nerve functional states of guinea pigs. Ten normal-hearing guinea pigs were implanted with CIs unilaterally. ECAPs were recorded both before and after the electrical stimulation, representing different functional states of the auditory nerve. Forward masking (FwdMsk) and alternating polarity (AltPol), two most commonly-used artifact-reduction methods, were applied to the measurements. All measurements recorded by the software were saved for computer and human analysis with linear regression and visual detection methods. ResultsThe correlations between human and computer performance in the peak-picking process were not affected by auditory nerve states and artifact-reduction methods. However, complicated findings were observed for ECAP threshold. With FwdMsk utilized, weaker correlations between human and computer performance were observed in abnormal state compared to those in normal state. Regardless of the functional states of the auditory nerve, the results revealed stronger correlations in AltPol than those in FwdMsk. Furthermore, when compared with human decision, computer linear-regression threshold (C-LRT) was always less accurate than computer visual-detection threshold (C-VDT), which was not affected by auditory nerve states. Conclusions(1) the functional states of the auditory nerve can definitely affect the correlations between human and computer decisions for ECAP threshold, but the impact is limited to the FwdMsk method; (2) AltPol can produce stronger correlations compared with FwdMsk, which is not affected by auditory nerve states; and (3) regardless of the auditory nerve states, C-VDT can always show higher consistency with human decision, while C-LRT reveals more variability.

Effect of Cochlear Implant Electrode Array Design on Electrophysiological and Psychophysical Measures: Lateral Wall versus Perimodiolar Types.

Background and ObjectivesThe present study aims to investigate whether the cochlear implant electrode array design affects the electrophysiological and psychophysical measures.Subjects and MethodsEighty five ears were used as data in this retrospective study. They were divided into two groups by the electrode array design: lateral wall type (LW) and perimodiolar type (PM). The electrode site was divided into three regions (basal, medial, apical). The evoked compound action potential (ECAP) threshold, T level, C level, dynamic range (DR), and aided air conduction threshold were measured. ResultsThe ECAP threshold was lower for the PM than for the LW, and decreased as the electrode site was closer to the apical region. The T level was lower for the PM than for the LW, and was lower on the apical region than on the other regions. The C level on the basal region was lower for the PM than for the LW whereas the C level was lower on the apical region than on the other regions. The DRs on the apical region was greater for the PM than for the LW whereas the DR was narrower on the apical region than on the other regions. The aided air conduction threshold was not different for the electrode design and frequency.ConclusionsThe current study would support the advantages of the PM over the LW in that the PM had the lower current level and greater DR, which could result in more localized neural stimulation and reduced power consumption.

Successful application and timing of a remote network for intraoperative objective measurements during cochlear implantation surgery

Objective: To determine the time needed to remotely perform a set of intraoperative measurements during cochlear implantation surgery and to compare it to the time needed to perform the same measurements in theatre.Design: Prospective two-arm study comparing a local with a remote measurement setting. Three intraoperative measurements (Impedance Field Telemetry (IFT), evoked compound action potential (ECAP) and evoked stapedius reflex test (eSRT)) were performed with the audiologist present in the operating theatre (i.e. locally) or with the audiologist in his/her office (i.e. remotely). The time needed to complete the measurements, in total and individually, were measured and compared.Study sample: Fifty cochlear implant recipients, aged 0.7–48 yearsResults: IFT, ECAP and eSRT were performed successfully in all participants. Comparing locally and remotely performed measurements, IFT did not differ significantly, ECAP threshold or slope did not differ significantly differ in any single channel and eSRT measurements did not differ significantly except for in one of six channels. Remote measurements took 8.6 min less to perform than did local measurements (10.04 vs. 18.64 min); a significant difference (p < 0.001).Conclusions: Using a remote network connection for intraoperative objective measurements is an efficient and safe way to perform measurements during cochlear implantation surgery.

Relationship between Electrically Evoked Compound Action Potential Thresholds and Auditory, Language, and Speech Progress after Cochlear Implant Surgery

Electrically evoked compound action potential (ECAP) is an objective auditory response that can be used in the programing of cochlear implants. The aims of this study were to monitor ECAP thresholds and auditory, language and speech progress for 6 months after cochlear implant surgery and to evaluate any relationship between them. Ten children with a mean age of 4.2 (±0.6) years and bilateral congenital and profound sensorineural hearing loss underwent cochlear implant surgery and post-operation auditory and speech training. The auditory, language, and speech abilities (Newsha level) and ECAP thresholds (for apical, medial and basal region of cochlea) were evaluated 1, 3 and 6 months after surgery. ECAP threshold showed no significant improvement in any of the evaluated areas in the 6 months after surgery (P>0.05); however, the Newsha level improved for all patients (P=0.00). There was no relationship between ECAP thresholds and auditory, language, and speech abilities (Newsha level) in the first 6 months after surgery. ECAP thresholds may be a poor indicator of improvement in auditory, language, and speech abilities, and depend on many factors.

Electrically evoked compound action potentials are different depending on the site of cochlear stimulation

One of the many parameters that can affect cochlear implant (CI) users’ performance is the site of presentation of electrical stimulation, from the CI, to the auditory nerve. Evoked compound action potential (ECAP) measurements are commonly used to verify nerve function by stimulating one electrode contact in the cochlea and recording the resulting action potentials on the other contacts of the electrode array.The present study aimed to determine if the ECAP amplitude differs between the apical, middle, and basal region of the cochlea, if double peak potentials were more likely in the apex than the basal region of the cochlea, and if there were differences in the ECAP threshold and recovery function across the cochlea.ECAP measurements were performed in the apical, middle, and basal region of the cochlea at fixed sites of stimulation with varying recording electrodes. One hundred and forty one adult subjects with severe to profound sensorineural hearing loss fitted with a Standard or FLEXSOFT electrode were included in this study. ECAP responses were captured using MAESTRO System Software (MED-EL). The ECAP amplitude, threshold, and slope were determined using amplitude growth sequences. The 50% recovery rate was assessed using independent single sequences that have two stimulation pulses (a masker and a probe pulse) separated by a variable inter-pulse interval. For all recordings, ECAP peaks were annotated semi-automatically.ECAP amplitudes were greater upon stimulation of the apical region compared to the basal region of the cochlea. ECAP slopes were steeper in the apical region compared to the basal region of the cochlea and ECAP thresholds were lower in the middle region compared to the basal region of the cochlea. The incidence of double peaks was greater upon stimulation of the apical region compared to the basal region of the cochlea.This data indicates that the site and intensity of cochlear stimulation affect ECAP properties.

Intraindividual comparison of psychophysical parameters between perimodiolar and lateral-type electrode arrays in patients with bilateral cochlear implants.

Perimodiolar electrode arrays were developed to improve stimulation of specific neuronal populations and to decrease power consumption; however, they can damage the cochlear structure. We examined and compared psychophysical parameters of perimodiolar and lateral-type electrode arrays in patients who received a different type of bilateral cochlear implant (CI) in each ear. Retrospective analysis. Tertiary referral center. Eight child patients (three males, five females) received a different CI in each ear (perimodiolar array and lateral array). They received the CIs sequentially (n = 7) or simultaneously (n = 1). Diagnostic, therapeutic, and rehabilitative. Electrically evoked compound action potential, threshold level, comfort level, and dynamic range (DR) of the basal, mid, and apical electrodes were compared. We also surveyed battery consumption for each device. Electrically evoked compound action potential threshold, threshold level, and comfort level were lower for the perimodiolar-type electrode array than for the lateral-type electrode array in most patients. However, the DR for the perimodiolar array was narrower than for the lateral array. For most patients, there was little difference in battery life. Although the level of electrical energy required for auditory stimulation seems to be lower for the perimodiolar electrode array than for the laterally placed array, the DR was wider and the amount of battery consumption was similar. The electrode array should be chosen by considering various patient factors, such as residual hearing.

Safety and Functional Results of Early Cochlear Implant Switch-On in Children

To assess the safety and the possible advantages of early (1-wk) cochlear implant switch-on in children and to compare impedance and ECAP threshold changes between subjects undergoing early switch-on and those undergoing traditional, 1-month switch-on. Prospective cohort study. Tertiary care referral pediatric center. Seventeen children receiving a unilateral or bilateral Nucleus Freedom cochlear implant were included, for a total of 20 ears. Ten ears were assigned to the early (1-wk) switch-on group and 10 to the control group (switch-on after 4 wks). Common ground impedance values and electrically evoked compound action potential thresholds were measured from intraoperation until 9 months postoperatively. Speech perception improvements over time were also assessed. Complication rate, impedance levels (kΩ), and electrically evoked compound action potentials (current levels) Early switch-on was well tolerated by patients and did not cause complications. Impedances dropped significantly after switch-on in both groups. They also seemed to achieve an earlier stability in the early switch-on patients, although the difference between groups was not significant. ECAP thresholds showed a similar, nonsignificant decreasing trend over time in both groups. Speech perception improvements did not differ between groups. This is the first study investigating the safety and the effects of an early cochlear implant switch-on in children. Results show that such a procedure is well tolerated by pediatric subjects and free from complications. Impedance measurements suggest that the earlier switched-on subjects benefit of lower and more stable impedances than subjects undergoing 1-month switch-on.

Measures of the electrically evoked compound action potential threshold and slope in HiRes 90KTM users

ObjectivesTo investigate electrically evoked compound action potentials (eCAPs) measured with the neural response imaging (NRI) ‘SmartNRI’ algorithm. NRI thresholds and slopes were examined according to three aspects: (1) site along the cochlea, (2) development of responses over time, and (3) influence of age/duration of deafness.MethodsThirty-four individuals implanted with the Advanced Bionics HiRes 90KTM device were included. The eCAP recordings were made from four electrodes along the array at first fitting and at frequent intervals up to at least 2 years. Slope and threshold (tNRI) of the amplitude growth function were measured and a range of explanatory variables were tested for significant effects on these measures using multi-factorial analysis of variance.ResultsElectrode position emerged as a significant effect for the tNRI measure, with lowest thresholds at the apical end of the array. Mean slope was greatest for the most apical electrode, but not significantly. Slope was significantly influenced by onset of deafness, with congenital hearing loss associated with steeper slopes than acquired hearing loss. There was also a highly significant effect of duration of device use, with a gradual increase in slope over the 2 years following device activation.DiscussionThe observed effects of electrode position are consistent with a model in which eCAP threshold is governed primarily by an effect of distance between electrode and neural interface (which is shorter towards the apex of the cochlea) and in which slope is governed primarily by density of surviving neural elements.

Determining Electrically Evoked Compound Action Potential Thresholds

Current cochlear implants (CIs) have telemetry capabilities for measuring the electrically evoked compound action potential (ECAP). Neural Response Telemetry (Cochlear) and Neural Response Imaging (Advanced Bionics [AB]) can measure ECAP responses across a range of stimulus levels to obtain an amplitude growth function. Software-specific algorithms automatically mark the leading negative peak, N1, and the following positive peak/plateau, P2, and apply linear regression to estimate ECAP threshold. Alternatively, clinicians may apply expert judgments to modify the peak markers placed by the software algorithms, or use visual detection to identify the lowest level yielding a measurable ECAP response. The goals of this study were to: (1) assess the variability between human and computer decisions for (a) marking N1 and P2 and (b) determining linear-regression threshold (LRT) and visual-detection threshold (VDT); and (2) compare LRT and VDT methods within and across human- and computer-decision methods. ECAP amplitude-growth functions were measured for three electrodes in each of 20 ears (10 Cochlear Nucleus® 24RE/CI512, and 10 AB CII/90K). LRT, defined as the current level yielding an ECAP with zero amplitude, was calculated for both computer- (C-LRT) and human-picked peaks (H-LRT). VDT, defined as the lowest level resulting in a measurable ECAP response, was also calculated for both computer- (C-VDT) and human-picked peaks (H-VDT). Because Neural Response Imaging assigns peak markers to all waveforms but does not include waveforms with amplitudes less than 20 μV in its regression calculation, C-VDT for AB subjects was defined as the lowest current level yielding an amplitude of 20 μV or more. Overall, there were significant correlations between human and computer decisions for peak-marker placement, LRT, and VDT for both manufacturers (r = 0.78-1.00, p < 0.001). For Cochlear devices, LRT and VDT correlated equally well for both computer- and human-picked peaks (r = 0.98-0.99, p < 0.001), which likely reflects the well-defined Neural Response Telemetry algorithm and the lower noise floor in the 24RE and CI512 devices. For AB devices, correlations between LRT and VDT for both peak-picker methods were weaker than for Cochlear devices (r = 0.69-0.85, p < 0.001), which likely reflect the higher noise floor of the system. Disagreement between computer and human decisions regarding the presence of an ECAP response occurred for 5 % of traces for Cochlear devices and 2.1 % of traces for AB devices. Results indicate that human and computer peak-picking methods can be used with similar accuracy for both Cochlear and AB devices. Either C-VDT or C-LRT can be used with equal confidence for Cochlear 24RE and CI512 recipients because both methods are strongly correlated with human decisions. However, for AB devices, greater variability exists between different threshold-determination methods. This finding should be considered in the context of using ECAP measures to assist with programming CIs.