Characteristics of electrically evoked potentials in patients with auditory neuropathy/auditory dys-synchrony.

The primary goal of this study was to compare the characteristics of the post-implant evoked potentials with preimplant evoked potentials in patients with auditory neuropathy (AN) or dys-synchrony. AN is typically characterized by sensorineural hearing loss, reduced speech perception, abnormal temporal processing, and unusual patterns of results with various objective audiological tests. In some cases, these patients may be appropriate candidates for a cochlear implant. In this article, we highlight evoked potential findings in two children diagnosed with AN who were provided with multichannel cochlear implants. Preoperative, interoperative and postoperative evoked potential measures show that the restoration of neural synchrony may occur at multiple levels of the auditory pathways in patients with AN when appropriate diagnostic tests, cochlear implantation and rehabilitation are provided.

Histopathology of cochlear implants in humans.

The insertion of an intrascalar electrode array during cochlear implantation causes immediate damage to the inner ear and may result in delayed onset of additional damage that may interfere with neuronal stimulation. To date, there have been reports on fewer than 50 temporal bone specimens from patients who had undergone implantation during life. The majority of these were single-channel implants, whereas the majority of implants inserted today are multichannel systems. This report presents the histopathologic findings in temporal bones from 8 individuals who in life had undergone multichannel cochlear implantation, with particular attention to the type and location of trauma and to long-term changes within the cochlea. The effect of these changes on spiral ganglion cell counts and the correlation between speech comprehension and spiral ganglion cell counts were calculated. In 4 of the 8 cases, the opposite, unimplanted ear was available for comparison. In 3 of the 4 cases, there was no significant difference between the spiral ganglion cell counts on the implanted and unimplanted sides. In addition, in this series of 8 cases, there was an apparent negative correlation between residual spiral ganglion cell count and hearing performance during life as measured by single-syllable word recognition. This finding suggests that abnormalities in the central auditory pathways are at least as important as spiral ganglion cell loss in limiting the performance of implant users.

Contralateral masking in cochlear implant users with residual hearing in the non-implanted ear.

Contralateral masking was investigated in cochlear implant users with residual hearing in the non-implanted ear. Threshold elevations for acoustic probes were observed when electrical maskers were presented in the opposite ear. Also, threshold elevations for electrical probes were observed when acoustic contralateral maskers were presented. The amount of threshold shift expressed in decibels charge or decibels sound pressure level produced by either contralateral acoustic or electric maskers was within the range found in normal listeners for similar stimuli (i.e. 4-8 dB). There was a correlation between the sensation level of acoustic maskers and the maximum amount of masking observed which is consistent with data for normally hearing subjects. The width of the masking patterns was similar to that expected from forward masking patterns in severely sensorineurally impaired ears and implanted ears. The maximum amount of acoustic masking tended to occur for electrode positions that were more basal than expected from characteristic frequency positions. However, where a relatively high-frequency 4-kHz masker could be used, there was a good match between the characteristic frequency position of the maximum threshold elevation and that of the masker.

Cochlear implants in five cases of auditory neuropathy: postoperative findings and progress.

OBJECTIVES: To review our experiences with some of the preoperative and postoperative findings in five children who were diagnosed with auditory neuropathy and were provided with cochlear implants. We describe changes in auditory function, which enabled these children to have significant improvement in their hearing and communication skills. STUDY DESIGN: Pre- and postoperatively, these children received complete medical examinations at Mayo Clinic, including related consultations in audiology, pediatrics, neurology, medical genetics, otolaryngology, psychology, speech pathology, and radiology. METHODS: These children typically had additional medical and audiological examinations at more than one medical center. The hearing assessments of these children included appropriate behavioral audiometric techniques, objective measures of middle ear function, acoustic reflex studies, transient (TOAE) or distortion product (DPOAE) otoacoustic emissions, auditory brainstem responses (ABR), and, in some cases, transtympanic electrocochleography (ECoG). After placement of the internal cochlear implant devices (Nucleus CI24), intraoperatively we measured electrode impedances, visually detected electrical stapedius reflexes (VESR) and neural response telemetry (NRT). These intraoperative objective measures were used to help program the speech processor for each child. Postoperatively, each child has had regular follow-up to assure complete healing of the surgical incision, to assess their general medical conditions, and for speech processor programming. Their hearing and communication skills have been assessed on a regular basis. Postoperatively, we have also repeated electrode impedance measurements, NRT measurements, otoacoustic emissions, and electrical auditory brainstem responses (EABR). We now have 1 year or more follow-up information on the five children. RESULTS: The five children implanted at Mayo Clinic Rochester have not had any postoperative medical or cochlear implant device complications. All of the children have shown significant improvements in their sound detection, speech perception abilities and communication skills. All of the children have shown evidence of good NRT results. All but case D (who was not tested) showed evidence of good postoperative EABR results. Otoacoustic emissions typically remained in the non-operated ear but, as expected, they are now absent in the operated ear. CONCLUSION: Our experiences with cochlear implantation for children diagnosed with auditory neuropathy have been very positive. The five children we have implanted have not had any complications postoperatively, and each child has shown improved listening and communication skills that have enabled each child to take advantage of different communication and educational options.

Objective intraoperative method to record averaged electromyographic stapedius muscle reflexes in cochlear implant patients.

We have developed a procedure to measure the averaged stapedius muscle reflex in response to electrical stimulation (AESR) with a cochlear implant. The AESR, as activated by ipsilateral stimulation with a cochlear implant, was investigated intra-operatively in a series of 12 children. After the cochlear implant was placed into the cochlea and secured by the surgeon, an electromyographic (EMG) needle electrode was gently placed into the stapedius muscle. During stimulation of the cochlear implant, the stapedius reflex was monitored visually (VESR) and as an averaged EMG response (AESR). Consistent AESRs were obtained in 7 of the 12 children. These measures provide a method to obtain stapedius muscle responses that may be helpful in the programming of young children with cochlear implants. Comparative post-operative measures were also obtained, including behavioral threshold levels, behavioral comfort levels, and the contralateral stapedius reflex threshold (ESR) on selected electrodes.

Neural response telemetry with the nucleus CI24M cochlear implant.

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

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

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

Facial nerve stimulation after Nucleus 22-channel cochlear implantation.

OBJECTIVE: To review the clinical features, radiographic findings, and programming strategies used in our population of patients who developed facial nerve stimulation after cochlear implantation. STUDY DESIGN AND SETTING: Patients referred to our nonprofit, outpatient facility were studied prospectively. PATIENTS: The study consisted of 14 patients with facial nerve stimulation after placement of the Nucleus 22-channel cochlear implant. INTERVENTIONS: Records were reviewed retrospectively, and patients were studied with three-dimensional computed tomographic scanning techniques. Electrical testing was performed, and various cochlear implant programming strategies were evaluated. MAIN OUTCOME MEASURES: Important clinical features were reviewed. The radiographic and anatomical relationships of the facial nerve to the cochlea were evaluated, and the programming strategies used to effectively control facial nerve stimulation were reviewed. RESULTS: Prevalence of facial nerve stimulation in our population was 7%. The most common cause was otosclerosis. Anatomical data confirmed the close proximity of the basal turn of the cochlea and the labyrinthine segment of the facial nerve. There was a high correlation between the electrodes causing symptoms and those found radiographically to be closest to the labyrinthine segment of the facial nerve. We were able to control facial nerve stimulation in all patients through programming mode changes. CONCLUSIONS: Otosclerosis appears to be a risk factor for developing facial nerve stimulation after cochlear implantation, and the site of stimulation appears to be the labyrinthine segment of the facial nerve. Familiarity with more elaborate programming techniques is critical to managing patients with this complication.

Cochlear implantation in the elderly.

The purpose of this study was to compare the audiologic and surgical results of elderly patients receiving cochlear implants with other adult patients, and to evaluate the benefit of cochlear implantation in the geriatric population. Twenty-eight patients, aged 60 to 80 years, who received the Nucleus 22 channel cochlear implant were studied retrospectively. Mean audiologic test scores increased significantly after implantation. Postoperative audiologic test scores of this elderly population are comparable to those of a matched group of younger adult patients. The surgical procedure was well tolerated in all elderly patients, and there were two postoperative complications requiring revision procedures. A questionnaire was used to assess implant use and the impact of cochlear implantation on the quality of life in this elderly population. Average implant use per day was 13.8 hours, and 65% of patients were able to recognize voices over the telephone. More than 80% of patients believed that their quality of life had improved significantly, that their self-confidence had increased, and that their decision regarding implantation was correct. The results of this study indicate that elderly patients with bilateral, profound, sensorineural hearing loss should not be denied consideration for cochlear implantation based on age alone.

Evaluation of a new spectral peak coding strategy for the Nucleus 22 Channel Cochlear Implant System.

Sixty-three postlinguistically deaf adults from four English-speaking countries participated in a 17-week field study of performance with a new speech coding strategy, Spectral Peak (SPEAK), and the most widely used strategy, Multipeak (MPEAK), both of which are implemented on wearable speech processors of the Nucleus 22 Channel Cochlear Implant System; MPEAK is a feature-extraction strategy, whereas SPEAK is a filterbank strategy. Subjects' performance was evaluated with an experimental design in which use of each strategy was reversed and replicated (ABAB). Average scores for speech tests presented sound-only at 70 dB SPL were higher with the SPEAK strategy than with the MPEAK strategy. For tests in quiet, mean scores for medial vowels were 74.8 percent versus 70.1 percent; for medial consonants, 68.6 percent versus 56.6 percent; for monosyllabic words, 33.8 percent versus 24.6 percent; and for sentences, 77.5 percent versus 67.4 percent. For tests in noise, mean scores for Four-Choice Spondees at +10 and +5 dB signal-to-noise ratio (S/N) were 88.5 percent versus 73.6 percent and 80.1 percent versus 62.3 percent, respectively; and for sentences at +15 dB, +10, and +5 dB S/N, 66.5 percent versus 43.4 percent, 61.5 percent versus 37.1 percent, and 60.4 percent versus 31.7 percent, respectively. Subjects showed marked improvement in recognition of sentences in noise with the new SPEAK filterbank strategy. These results agree closely with subjects' responses to a questionnaire on which approximately 80 percent reported they heard best with the SPEAK strategy for everyday listening situations.

Objective electrophysiological measures from cochlear implant patients.

Various objective electrophysiological techniques have been used to supplement the behavioral measurements for cochlear implant patients. This report summarizes various studies of these measurements, including stimulus artifact, averaged electrode voltages, electrical stapedius reflexes, electrical auditory brain stem responses, electrical middle latency responses, and cortical auditory responses. These techniques have been shown to provide valuable information in the evaluation of device and electrode integrity in addition to correlated values to behavioral thresholds and comfort levels.

Combined electrical and acoustical stimulation using a bimodal prosthesis.

A new device incorporating a cochlear implant speech processor and a speech-processing hearing aid for the unimplanted ear has been designed and tested with four severely hearing-impaired patients. The aim of the device is to provide a more acceptable and effective combination of electrical and acoustic signals to the two ears. When used monaurally, and binaurally in conjunction with the cochlear implant, the speech-processing hearing aid mean scores for open-set sentences, words, and consonants were as good as or better than the mean scores for the patients' own conventional hearing aids. Some patients improved much more than did others. Although not conclusive, these results are encouraging, especially as they were achieved with a laboratory prototype that did not allow the patients to become accustomed to the processor in everyday situations.