Biomedical subjects

T A Zwolan

Publications and source records attributed to T A Zwolan.

At least 19 recordsLinked to original sources

PubMed2004

Pediatric cochlear implant patient performance as a function of age at implantation.

OBJECTIVE: The objective of this study was to examine the effect that age at implantation has on performance of children who received multichannel cochlear implants. STUDY DESIGN: This is a retrospective study of 295 children who were broken down into 5 age groups based on age at implantation: 1-3 years, 3-5 years, 5-7 years, 7-9 years, and 9-11 years. Speech perception test scores obtained 12, 24, and 36 months postactivation were compared for the 5 groups using repeated-measures analysis of variance. SETTING: This study was carried out at a tertiary academic medical center. PATIENTS: Subjects consisted of 295 children who ranged in age from 12 months to 10 years 11 months at the time they obtained their cochlear implant. INTERVENTION: All patients received their cochlear implant at a single implant facility. MAIN OUTCOME MEASURES: Performance on several speech perception tests was compared 12, 24, and 36 months postactivation. Performance was evaluated as a function of age at implantation. RESULTS: Patients in all 5 groups demonstrated improved scores when compared with scores obtained preoperatively with hearing aids. Repeated-measures analysis of variance (ANOVA) revealed a significant group by time interaction for 3 of the 5 measures. For all three of these measures, children implanted at younger ages demonstrated greater gains in speech perception over time than children implanted at older ages. CONCLUSIONS: These results are in agreement with those of previous studies indicating that early implantation facilitates improved development of speech perception skills in profoundly deaf children.

Age Factors↗

PubMed2001

Effects of electrode configuration and place of stimulation on speech perception with cochlear prostheses.

Recent research and clinical experience with cochlear implants suggest that subjects' speech recognition with monopolar or broad bipolar stimulation might be equal to or better than that obtained with narrow bipolar stimulation or other spatially restricted electrode configurations. Furthermore, subjects often prefer the monopolar configurations. The mechanisms underlying these effects are not clear. Two hypotheses are (a) that broader configurations excite more neurons resulting in a more detailed and robust neural representation of the signal and (b) that broader configurations achieve a better spatial distribution of the excited neurons. In this study we compared the effects of electrode configuration and the effects of longitudinal placement and spacing of the active electrodes on speech recognition in human subjects. We used experimental processor maps consisting of 11 active electrodes in a 22-electrode scala tympani array. Narrow bipolar (BP), wide bipolar (BP + 6), and monopolar (MP2) configurations were tested with various locations of active electrodes. We tested basal, centered, and apical locations (with adjacent active electrodes) and spatially distributed locations (with every other electrode active) with electrode configuration held constant. Ten postlingually deafened adult human subjects with Nucleus prostheses were tested using the SPEAK processing strategy. The effects of electrode configuration and longitudinal place of stimulation on recognition of CNC phonemes and words in quiet and CUNY sentences in noise (+10 dB S/N) were similar. Both independent variables had large effects on speech recognition and there were interactions between these variables. These results suggest that the effects of electrode configuration on speech recognition might be due, in part, to differences among the various configurations in the spatial location of stimulation. Correlations of subjective judgments of sound quality with speech-recognition ability were moderate, suggesting that the mechanisms contributing to subjective quality and speech-recognition ability do not completely overlap.

Adult↗

PubMed2001

The influence of age at implantation on performance with a cochlear implant in children.

OBJECTIVE: This study involved the assessment of speech recognition abilities as a function of age at implantation and length of cochlear implant use in children who received the Nucleus CI22M cochlear implant. STUDY DESIGN: Two separate analyses were performed. The first analysis involved the assessment of speech recognition performance as a function of length of time with a cochlear implant in 48 patients evaluated at 7 years of age. The second analysis involved the assessment of speech recognition performance as a function of age at implantation in 53 patients evaluated 36 months after implantation. Patients were divided into four groups based on length of implant use or age at implantation, and the results were analyzed by a repeated-measures analysis of variance. SETTING: This study was carried out at a tertiary academic medical center. PATIENTS: Patients consisted of children implanted with a Nucleus Multi Channel cochlear implant programmed with the SPEAK encoding strategy. Their ages at the time of evaluation ranged from 5.5 to 7.8 years. Their ages at implantation ranged from 2.4 to 14.5 years. INTERVENTIONS: All patients received a Nucleus Multi Channel cochlear implant programmed with the SPEAK encoding strategy. Word and sentence recognition tests were administered at various ages and at several postimplantation intervals. MAIN OUTCOME MEASURES: Performance as a function of length of cochlear implant use and as a function of age at implantation. RESULTS: Patients performed significantly better as length of cochlear implant use increased and age at implantation decreased. When patients were tested at a fixed postimplantation time interval (36 months), there was an overall trend for patients who received the implant at a younger age to perform better in spite of being younger at the time of evaluation. However, these effects were not statistically significant for all speech recognition tests that were administered. CONCLUSIONS: These results confirm previous findings indicating continued improvement of speech recognition with time in implanted children. Furthermore, the results support the concept of the advantage of a younger age at implantation.

Adolescent↗

PubMed2001

Implantation of the malformed cochlea.

OBJECTIVE: This study assesses the results of cochlear implantation in children with cochlear malformations. STUDY DESIGN: Retrospective, matched-pairs analysis of prospectively collected data. SETTING: University-based regional cochlear implant center. PATIENTS: Seventeen children with osseous cochlear malformations who had undergone implantation were matched and compared with a group of children with normal cochleae who had undergone implantation. INTERVENTIONS: All subjects received a multichannel cochlear implant and habilitation. MAIN OUTCOME MEASURES: All subjects were tested with the Early Speech Perception test, and the Glendonald Auditory Speech Perception tests for words and sentences. Patients were classified in a standardized speech perception category based on performance on the Early Speech Perception test. RESULTS: All subjects demonstrated improving performance on all measures of speech perception over time. Overall, the two groups showed no statistically significant differences in performance at 6 and 24 months. However, subjects with malformed cochleae evidenced slower rates of improvement than did their matched control subjects. Subjects with more severe malformations demonstrated poorer performance, but this may have been attributable to preoperative factors rather than to implant performance. CONCLUSIONS: Children with radiographic cochlear malformations benefit from cochlear implantation with multichannel devices. They ultimately perform as well as their matched counterparts with normal cochleae, although they may improve more slowly over time.

Child↗

PubMed2000

Speech, vocabulary, and the education of children using cochlear implants: oral or total communication?

This study examines the relationship between the teaching method, oral or total communication, used at children's schools and children's consonant-production accuracy and vocabulary development over time. Children who participated in the study (N = 147) demonstrated profound sensorineural hearing loss and had used cochlear implants for between 6 months and 10 years. Educational programs that used an oral communication (OC) approach focused on the development of spoken language, whereas educational programs that used a total communication (TC) approach focused on the development of language using both signed and spoken language. Using Hierarchical Linear Modeling (HLM) we compared the consonant-production accuracy, receptive spoken vocabulary, and expressive spoken and/or signed vocabulary skills, over time, of children who were enrolled in schools that used either OC or TC approaches, while controlling for a number of variables. These variables included age at implantation, preoperative aided speech detection thresholds, type of cochlear implant device used, and whether a complete or incomplete active electrode array was implanted. The results of this study indicated that as they used their implants the children demonstrated improved consonant-production accuracy and expressive and receptive vocabulary over time, regardless of whether their school employed a TC or OC teaching method. Furthermore, there appeared to be a complex relationship among children's performance with the cochlear implant, age at implantation, and communication/teaching strategy employed by the school. Controlling for all variables, children in OC programs demonstrated, on average, superior consonant-production accuracy, with significantly greater rates of improvement in consonant-production accuracy scores over time compared to children in TC programs. However, there was no significant difference between OC and TC groups in performance or rate of growth in consonant-production accuracy when children received their implants before the age of 5 years. There was no significant difference between the OC and TC groups in receptive spoken vocabulary scores or in rate of improvement over time. However, children in the TC group achieved significantly higher receptive spoken vocabulary scores than children in the OC group if they received their implant before the age of 5 years. The TC group demonstrated superior scores and rates of growth on the expressive vocabulary measure (spoken and/or signed) when compared to the OC group if they received their implants during their preschool or early elementary school years. There was no significant difference if the children received their implants during middle elementary school. Regardless of whether children were in the OC or TC group, children who received their implants during preschool demonstrated stronger performance, on average, on all measures over time than children who received their implants during their elementary school years. The results of this study suggest that children may benefit from using cochlear implants regardless of the communication strategy/teaching approach employed by their school program and that other considerations, such as the age at which children receive implants, are more important. Implications and future research needs are discussed.

Child Language↗

PubMed1999

Effects of stimulus level on electrode-place discrimination in human subjects with cochlear implants.

Effects of stimulus level on discrimination of one stimulation site from another were examined in 15 human subjects with Nucleus-22 cochlear implant systems. Bipolar stimulation was used in all cases with electrodes in the bipolar pair separated by 1.5 mm (center to center). Subjects were first tested at a medium loudness level, using an adaptive tracking procedure, to determine the regions of the electrode array where electrode-place discrimination was best and the regions where it was poorest. Electrode-place discrimination was then tested at three regions distributed throughout the array, which included the regions of best and poorest discrimination. At each region, electrode-place discrimination was tested at three levels: 25%, 50%, and 75% of the dynamic range. For each of these nine conditions (3 sites x 3 levels), the test-electrode pairs were loudness balanced with the reference-electrode pairs. A two-interval forced-choice same-different procedure was then used to determine discriminability of the reference-electrode pair from the nearest, apical, test-electrode pair. If P(C)max was <0.707 at all three levels, additional testing was done using the next, more apical, electrode pair as the test-electrode pair. A tendency toward better discrimination at more apical regions of the array was observed. Electrode pairs with poor discrimination typically had smaller dynamic ranges than those with good discrimination. There was a weak tendency toward better discrimination at higher levels of stimulation. However, effects of level on electrode-place discrimination were less pronounced and less consistent than previously observed effects of level on temporal discriminations. These results suggest interactions between current spread and the condition of the implanted cochlea as underlying mechanisms.

Adult↗

PubMed1998

Performance with the 20 + 2L lateral wall cochlear implant.

OBJECTIVE: The purpose of this study was to investigate the operating characteristics of the Nucleus 20 + 2L lateral wall cochlear implant including speech recognition results. STUDY DESIGN: This was a prospective randomized study involving five different modes of stimulation. SETTING: This study was carried out in an academic, tertiary referral center. PATIENTS: The patients included in this study were adult cochlear implant candidates ages 44-74 years. Length of deafness ranged from 1 to 58 years with a variety of etiologies. INTERVENTIONS: All patients were implanted with a 20 + 2L implant, which includes an intrascalar electrode array and an apically placed extracochlear, titanium encased ball electrode in contact with the endosteum of the apical turn. All patients underwent psychophysical and speech recognition testing in five different modes of electrode configuration. MAIN OUTCOME MEASURE(S): The main outcome measures included thresholds, comfort levels, dynamic ranges, and speech recognition results obtained in five electrode configuration modes. RESULTS: Thresholds were significantly lower (repeated measures ANOVA) in both monopolar conditions when compared to bipolar mode of stimulation. A binomial statistical analysis indicated that in five of nine patients activated in all five modes of stimulation, the monopolar modes of stimulation resulted in improved speech recognition scores. CONCLUSIONS: The results of the study demonstrate the feasibility of the use of an apical lateral cochlear wall electrode in conjunction with an intrascalar electrode array. It further demonstrated the superiority of monopolar stimulation in selected patients.

Adult↗

PubMed1997

Effects of stimulus configuration on psychophysical operating levels and on speech recognition with cochlear implants.

Effects of electrode configuration and pulse duration on operating levels and on speech recognition performance were studied in a group of 14 adult postlingually deaf human subjects with Nucleus cochlear implants. The operating levels (based on detection threshold and maximum comfortable loudness levels) for narrowly spaced bipolar (BP) stimulation were found to be about 11 dB higher on average than those for widely spaced bipolar (BP+6) or monopolar (MP1) stimulation. Operating levels for common ground (CG) stimulation fell between those for BP and BP+6; the difference between BP and CG detection thresholds depended on pulse duration. Variation in detection thresholds and maximum comfortable loudness levels across the electrode array (electrodes 1-15) was larger for BP and CG stimulation than for BP+6 or MP1 stimulation, suggesting narrower spread of activation for the BP and CG configurations despite the higher current levels. Speech recognition performance was tested using experimental processor configurations. Among the experimental electrode configurations tested (BP, CG, and BP+6), the highest speech recognition scores were obtained with the BP+6 configuration in many subjects. Effects of pulse duration on speech recognition were less consistent and usually smaller than the effects of electrode configuration. The results indicate that electrode configuration is an important variable determining speech recognition performance and suggest that restriction of the size of neural population activated by individual channels of the prosthesis is not necessarily advantageous.

Adult↗

PubMed1997

Cochlear implantation of children with minimal open-set speech recognition skills.

OBJECTIVE: The purpose of this study was to evaluate the postoperative performance of 12 children who demonstrated some open-set speech recognition skills before receiving a Nucleus multichannel cochlear implant with a view toward expanding the selection criteria for cochlear implant candidacy to include children who derive minimal benefit from amplification. DESIGN: Pre- and postoperative performance of two groups of children were compared. Group 1 consisted of 12 children who demonstrated some open-set speech recognition skills before receiving a Nucleus multichannel cochlear implant (Borderline group). Group 2 consisted of 12 children who demonstrated no open-set speech recognition skills before implantation with a Nucleus device (Traditional group). In all children, candidacy was determined based on preimplant binaural aided performance. For most subjects, the poorer ear was selected for implantation. Mean pre- and postoperative speech recognition scores of the Borderline subjects were compared to determine the benefit provided by their cochlear implants. Secondly, matched-pair analyses were used to compare the mean speech recognition scores obtained by the Borderline and Traditional subjects. RESULTS: The scores of the Borderline group improved significantly on five of six speech recognition measures when 6 mo postoperative scores obtained with the implant were compared with preoperative test scores obtained with hearing aids. By the 12 mo postoperative interval, the scores of the Borderline group had improved significantly (p < 0.05) on all six measures. In contrast, scores obtained by the Traditional group had improved significantly on three of six measures at both the 6 and 12 mo postoperative intervals. Comparison of postoperative test scores revealed that the Borderline group scored significantly higher than the Traditional group on three of six measures at the 6 mo test interval and on six of six measures at the 12 mo test interval (p < 0.05). CONCLUSIONS: The findings of this study indicate that both groups derive significant benefit from their cochlear implants. Although the mean preoperative audiograms for the implanted ears did not differ significantly for the two groups of subjects, members of the Borderline group exhibited significantly better speech recognition skills than the Traditional group during the first year after implantation. These findings suggest that the increased auditory experience of the Borderline subjects positively influenced their performance with a cochlear implant. The authors advocate that the selection criteria used to determine pediatric cochlear implant candidacy be broadened to include consideration of children who demonstrate minimal open-set speech recognition skills.

Child↗

PubMed1997

Comparison of electrode discrimination, pitch ranking, and pitch scaling data in postlingually deafened adult cochlear implant subjects.

The goal of this study was to investigate the relationship between variation in electrode site of stimulation and the perceptual dimensions along which such stimuli vary. This information may allow more effective use of electrode place when encoding speech information. To achieve this goal, two procedures which measure pitch in subjects implanted with the Nucleus/Cochlear Corporation multichannel device were performed. Estimates of electrode discriminability that can be obtained from these procedures were compared to a more direct measure of electrode discriminability that was obtained in a previous study [Collins et al., Assoc. Res. Otolaryng. Abstracts, No. 642 (1994)]. In the first task, subjects performed a pitch ranking procedure similar to that used in previous studies [Townshend et al., J. Acoust. Soc. Am. 82, 106-115 (1987); Nelson et al., J. Acoust. Soc. Am. 98, 1987-1999 (1995)]. Estimates of the pitch percept elicited by stimulation of each electrode as well as the discriminability of the electrodes were generated from the data using two different statistical analyses. In the second task, subjects performed a pitch scaling procedure similar to one used in a previous study [Busby et al., J. Acoust. Soc. Am. 95, 2658-2669 (1994)]. Again, two different statistical analyses were performed to generate estimates of the pitch percept corresponding to stimulation of each electrode and to generate estimates of electrode discriminability. In general, the estimates of the relationships between the pitch percepts obtained from the two procedures were not identical. In addition, the estimates of electrode discriminability were not equivalent to the electrode discrimination measures obtained from the same subjects during the previous study. Signal detection theory has been used to model the decision processes required by each of the procedures described above [e.g., Jesteadt and Bilger, J. Acoust. Soc. Am. 55, 1266-1276 (1974)]. However, these models do not predict the differences that were observed between the data sets obtained during this study. An alternate model is proposed which may explain the data obtained from these subjects. This model is based on the assumption that the percept that is elicited by electrical stimulation of an electrode is multidimensional, as opposed to unidimensional in nature. Therefore, the perceived signal is more appropriately modeled using a multidimensional random vector, where each element of the vector represents the perceived value of one of the dimensions of the signal.

Adult↗

PubMed1997

Electrode discrimination and speech recognition in postlingually deafened adult cochlear implant subjects.

This study investigated the relationship between electrode discrimination and speech recognition in 11 postlingually deafened adult cochlear implant subjects who were implanted with the Nucleus/Cochlear Corporation multichannel device. The discriminability of each electrode included in a subject's clinical map was measured using adaptive and fixed-level discrimination tasks. Considerable variability in electrode discriminability was observed across subjects. Two subjects could discriminate all electrodes, and discrimination performance by the remaining nine subjects varied from near perfect to very poor. In these nine subjects, the results obtained from the discrimination tasks were used to create a map that contained only discriminable electrodes, and subjects' performance on speech recognition tasks using this experimental map was measured. Four different speech recognition tests were administered: a nine-choice closed-set medial vowel recognition task, a 14-choice closed-set medial consonant recognition task, the NU6 Monosyllabic Words Test [T. W. Tillman and T. Carhart, Tech. Rep. No. SAM-TR-66-55, USAF School of Aerospace Medicine, Brooks Air Force Base, Texas (1966)] scored for both words and phonemes correct, and the Central Institute for the Deaf (CID) Everyday Sentences test [H. Davis and S. R. Silverman, Hearing and Deafness (Holt, Rinehart, and Winston, New York, 1978)]. Seven of the nine subjects tested with the experimental map showed significant improvement on at least one speech recognition measure, even though the experimental map contained fewer electrodes than the original map. Three subjects' scores improved significantly on the CID Everyday Sentences test, three subjects' scores improved significantly on the NU6 Monosyllabic Words test, and five subjects' scores improved significantly on the NU6 Monosyllabic Words test scored for phonemes correct. None of the subjects' scores improved significantly on either the vowel or consonant tests. No significant correlation was observed between electrode discrimination ability and speech recognition scores or between electrode discrimination ability and improvement in speech recognition scores when programmed with the experimental map. The results of this study suggest that electrode discrimination tasks may be used to improve speech recognition of some cochlear implant subjects, and that each electrode site does not necessarily provide perceptually distinct information.

Adult↗

PubMed1997

Electrically evoked auditory potentials: current clinical applications in children with cochlear implants.

OBJECTIVE: To summarize the current applications of auditory evoked potential in children with cochlear implants and candidates for implantation. PATIENTS AND METHODS: Perioperative transtympanic EABR is used routinely for ear selection and to establish the electrical stimulability of the ear intended to be implanted. The perioperative transtympanic EABR is supplemented with EABR obtained immediately following the insertion of the electrode array and the seating of the implant's receiver. Postoperatively, EABR and averaged electrode voltages are used effectively to properly adjust the implant stimulus parameters and to determine whether the implant is functioning adequately. Postoperatively, cognitive evoked potentials to speech and tonal stimuli may also be obtained. RESULTS: EABR results have contributed to effective implant placement and function. There were several significant correlations between speech recognition and cognitive evoked potential. CONCLUSION: These measures help assure proper implant function and effective stimulus delivery.

Adolescent↗

PubMed1996

Self-report of cochlear implant use and satisfaction by prelingually deafened adults.

OBJECTIVE: Prelingually deafened adults tend to demonstrate smaller improvements in speech recognition after cochlear implantation than do postlingually deafened adults, which has led some professionals to believe that prelingually deafened adults receive only minimal benefit from a cochlear implant. The primary objective of this study was to evaluate cochlear implant use and satisfaction by prelingually deafened adults. DESIGN: A questionnaire was administered to 12 prelingually deafened adult cochlear implant patients to evaluate cochlear implant efficacy and satisfaction. Questionnaire results were contrasted with performance on speech recognition tasks. RESULTS: Although these patients demonstrated little or no improvements in speech recognition 12 mo postoperatively, most patients reported that they used their device regularly, that they were satisfied with their device, and that using the cochlear implant improved both their expressive and receptive communication skills. CONCLUSIONS: Procedures other than traditional speech recognition measures should be used to evaluate cochlear implant benefit, particularly with prelingually deafened adults.

Adult↗

PubMed1996

Patient performance with the Cochlear Corporation "20 + 2" implant: bipolar versus monopolar activation.

A within-subjects comparison of monopolar versus bipolar stimulation was performed using a modified version of the Nucleus mini-22 cochlear implant, the Nucleus "20 + 2" implant. Six subjects underwent implantation with this device, which is identical to the Nucleus 22 cochlear implant with the addition of two extracochlear indifferent electrodes. These electrodes provide two monopolar modes of stimulation in addition to the standard bipolar modes used with the Nucleus 22 device. One of the indifferent electrodes is a ball placed under the temporalis muscle (MP1), whereas the second electrode is mounted on the lateral aspect of the receiver-stimulator (MP2). After a pre-experimental phase, subjects used each of three stimulation modes (BP + 1, MP1, and MP2) for a total of 4 weeks each. Variables tested with each mode included electric thresholds, comfort levels, dynamic ranges, and speech recognition. Both the MP1 and MP2 modes of stimulation required significantly less current than the bipolar mode (BP + 1) to reach threshold and comfort level. Analysis of dynamic range data also indicated a significant stimulation mode effect. However, stimulation in the various modes did not significantly affect speech recognition scores, although two subjects demonstrated significantly improved speech recognition scores when programmed in a monopolar mode.

Adult↗

PubMed1995

Cochlear implantation in patients with cochlear malformations.

OBJECTIVE: To report operative findings, postoperative course, and postimplantation performance in patients with cochlear malformations who underwent cochlear implantation. DESIGN: Case study and intervention study (before-after trial). Minimum follow-up of 12 months; average follow-up of 24 months. SETTING: Academic tertiary referral center. PATIENTS: Six patients, including five children who underwent implantation at ages 3.5 to 13 years and one adult who underwent implantation at age 27 years. malformations included common cavity deformity (n = 1), cochlear hypoplasia (n = 2), and incomplete partition (n = 3). All patients with cochlear malformations who underwent implantation at the University of Michigan, Ann Arbor, are included, selected from a group of 196 patients so treated since 1986. INTERVENTION: Implantation with a standard multichannel cochlear implant. MAIN OUTCOME MEASURES: Operative findings described include round window and facial nerve anatomy and cerebrospinal fluid leak. Postoperative roentgenographic findings, electrode activation, and reason for non-use of electrodes were investigated. Standard tests of speech perception were used to compare preoperative and postoperative performance for each subject. RESULTS: Operative findings included round window abnormalities (three patients), anomalous facial nerve (one patient), and cerebrospinal fluid leak (three patients). No surgical complications occurred. A minimum of 10 electrodes were activated for all patients. Electrode thresholds and discomfort levels were variable for several months after implantation. All patients demonstrated improved performance after implantation. Four subjects demonstrated open-set speech perception. Two other subjects, whose poor language skills precluded administration of standard tests, showed increased awareness of environmental sounds and increased vocalization after implantation. CONCLUSIONS: Cochlear implantation can be a successful method of rehabilitation in patients with congenital deafness who have cochlear malformations.

Adolescent↗

PubMed1995

Effects of electrical current configuration on stimulus detection.

Psychophysical detection of electrical stimulation of the cochlea was studied as a function of electrical-current configuration. Subjects were postlingually deaf humans with Nucleus 20 + 2, Nucleus 22, and Ineraid cochlear implants and nonhuman primates unilaterally deafened and implanted with a multielectrode array similar to the Nucleus implant. In nonhuman primate and human Ineraid subjects, which had percutaneous connectors, we compared threshold functions for sinusoids and pulse trains for quadrupolar, bipolar, monopolar, and parallel multipolar stimulation. Thresholds decreased across this set of configurations. In some cases, the effects of current configuration were dependent on sinusoidal frequency and pulse duration. Pulse duration-dependent effects were also seen when comparing bipolar, monopolar, and common-ground configurations. Bipolar and monopolar stimulation were compared in Nucleus subjects using pulse trains at 50 microseconds per phase. For bipolar stimulation, thresholds decreased as a function of electrode separation, reaching a level near that for monopolar stimulation at separations of 3.5 to 6.5 mm in most cases. These results may be interpreted in terms of effects of current configuration on the magnitude and shape of electrical-potential fields produced in the cochlea, although more central factors also play a role in determining psychophysical detection thresholds.

Animals↗

PubMed1995

Cochlear implant device failure: diagnosis and management.

Complete, irreversible failure of the implanted receiver-stimulator of the Cochlear Corporation multichannel implant are relatively rare. However, as the implanted patient population grows, malfunctions may be expected. From the over 200 patients implanted at the University of Michigan Medical Center, 6 patients with a complete and irreversible cochlear implant receiver-stimulator failure have been identified and treated. This represents a 3% failure rate. The amount of time between initial implantation and device failure ranged from 6 months to 3.5 years. Determination of device failure was made using psychophysical, electrophysiologic, and averaged electrode voltage measurements. The measurement of the average electrode voltages proved to be useful in determining the condition of the implant. Physiologic changes causing reduced electrical excitability were ruled out using psychophysical or electrophysiologic promontory testing. All patients were successfully explanted and reimplanted.

Adult↗

PubMed1994

Electrically evoked auditory brain-stem response in pediatric patients with cochlear implants.

OBJECTIVE: To study the feasibility and clinical applicability of preoperative, transtympanic electrically evoked auditory brain-stem response (EABR) in a pediatric patient population with cochlear implants. DESIGN: A descriptive study using repeated measures analyses of variance to determine if EABR measures were affected by response configuration or cochlear status. SETTING: The operating room before cochlear implant surgery. PATIENTS: A population-based sample of 43 patients aged 2.5 to 14.5 years who were candidates for cochlear implantation. INTERVENTION: Stimuli consisting of brief balanced biphasic current pulses were provided by a transtympanically placed promontory needle electrode; EABR was recorded with subdermal needle electrodes on the forehead and contralateral mastoid. MAIN OUTCOME MEASURE: Presence or absence of postoperative electrical excitability with a cochlear implant. RESULTS: Electrically evoked auditory brain-stem responses were available from 41 of the 43 patients tested. Mean EABR threshold was 406.5 microA (SD = 118.1) for 31 patients with patent cochleas and 472 microA (SD = 91) for 10 patients with cochlear ossification. Mean wave V latency at threshold was 4.69 milliseconds (SD = 0.57). CONCLUSION: Preoperative EABR is an integral component of the preoperative selection process for pediatric patients with cochlear implants.

Adolescent↗