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Biomedical subjects

Kevin H Franck

Publications and source records attributed to Kevin H Franck.

8 recordsLinked to original sources
PubMed2005

Electrode interaction in pediatric cochlear implant subjects.

Multielectrode cochlear implants rely on differential stimulation of the cochlear nerve for presenting the brain with the spectral and timing information required to understand speech. In implant patients, the degree of overlap among cochlear nerve fibers stimulated by the different electrodes constitutes the electrode interaction. Electrode interaction degrades the spectral resolution of the implant's stimulus. We sought to define electrode interaction in a cohort of pediatric cochlear implant subjects as a function of both stimulus intensity and electrode location along the array. The 27 pediatric subjects that completed the study were implanted with either the Clarion Hi-Focus array with or without positioner, the Nucleus 24 Contour array, or the Nucleus 24 Straight array. All but two of the patients had congenital hearing loss, and none of the patients had meningitis prior to the onset of deafness. The cochlear nerve response was measured with the electrically evoked compound action potential (ECAP). A forward masking protocol was used such that a probe stimulus electrode remained fixed while a preceding masker was moved across the array. Electrode interaction was estimated by measuring the unmasked probe response minus the masked probe response. Three probe locations and three probe intensities were examined for each subject. At all probe locations, electrode interaction increased as probe intensity increased (p < 0.05). Interaction at the basal probe was less than that at either the middle or apical probe locations (p < 0.05), and significant correlation found between probe distance from the basal end of the array and electrode interaction (p < 0.001). These results demonstrate that in this cohort of pediatric subjects, electrode interaction depended on both stimulus intensity and probe location. Implications of these findings on future implant array design and current implant fitting strategies are discussed. The impact of electrode interaction on implant performance is yet to be elucidated.

Artifacts↗
PubMed2004

Electrically evoked compound action potential amplitude growth functions and HiResolution programming levels in pediatric CII implant subjects.

OBJECTIVE: To characterize the amplitude growth functions of the electrically evoked compound action potential (ECAP) in pediatric subjects implanted with the Clarion HiFocus electrode array with respect to electrode position and the presence or absence of a Silastic positioner. Electrophysiologic growth function data are compared with HiResolution (HiRes) psychophysical programming levels. DESIGN: ECAP growth functions were measured for all electrodes along the implant's array in 16 pediatric subjects. Nine of the patients were implanted with a Silastic positioner, whereas seven had no positioner. ECAP thresholds and growth function slopes were calculated. Fifteen of the 16 patients had psychophysical threshold and maximum comfort levels available. Programming levels and ECAP thresholds were compared within and among the subjects. RESULTS: ECAP thresholds showed variability among patients, ranging from 178 to 920 nA at 32 musec pulse width. ECAP thresholds did not depend on electrode position along the cochlea but were lower in the presence of the Silastic positioner (p < 0.001). Thresholds determined with the masker-probe versus the alternating polarity paradigms revealed moderate (r = 0.76) correlation. Growth function slopes also showed considerable variation among patients. Unlike thresholds, slopes decreased from apical to basal cochlear locations (p < 0.001) but showed no difference between the absence and presence of the positioner. Programming levels in HiRes were correlated with ECAP threshold levels. When ECAP thresholds were adjusted for each patient by the difference between M level and ECAP threshold at electrode 9, however, overall correlation between the two measurements was excellent (r = 0.98, N = 224). CONCLUSIONS: In pediatric subjects with the Clarion HiFocus electrode, ECAP growth function thresholds appear to decrease with the presence of the Silastic positioner but are unaffected by electrode position along the array. Growth function slope, however, depends on electrode position along the array but not on the presence of the positioner. ECAP programming levels can reliably predict stimulus intensities within the patients' dynamic ranges, but considerable variability is seen between ECAP thresholds and HiRes programming levels.

Acoustic Impedance Tests↗
PubMed2004

Averaged electrode voltage testing to diagnose an unusual cochlear implant internal device failure.

This paper describes an unusual Clarion 1.2 cochlear implant failure in order to demonstrate the need for the clinical availability of electrode voltage testing. The case report describes a patient with a Clarion 1.2 cochlear implant who exhibited poor auditory progress in spite of grossly normal impedances and electric field testing, and an appropriate educational and psychosocial environment. For a subset of electrodes, however, electrode voltage testing was abnormal. At explantation it was found that the epoxy that protects the connection between the electrode leads of the array and the output contacts on the internal controller had fractured. This failure was not associated with reported head trauma. This case report demonstrates the utility of and clinical need for electrode voltage testing as a helpful tool to diagnose internal device failure.

Child, Preschool↗
PubMed2002

Effects of stimulus level on speech perception with cochlear prostheses.

This study is one of a series that examines stimulus features important for cochlear implant function. Here, we examine effects of stimulus level. In subjects with cochlear implants, a number of psychophysical tests of temporal discrimination (pulse rate discrimination, gap detection, etc.) show marked improvement as a function of stimulus level through most or all of the dynamic range, while electrode-place discrimination can improve or degrade as a function of level. In this study, effects of these combined potential influences were studied by examining the effects of stimulus level on syllable identification. We tested two hypotheses: that syllable identification varies as a function of stimulus level and that level and electrode configuration interact in affecting syllable identification. We examined vowel and consonant identification as a function of stimulus level for bipolar and monopolar electrode configurations. We used experimental processor maps where upper and lower stimulation limits of each electrode pair were equated to eliminate confounding effects of dynamic range, which varies across subjects and electrodes. For each channel, stimulation amplitude was set to a fixed percentage of its dynamic range. Eight adult subjects with Nucleus CI24M implants were tested using the SPEAK processing strategy. With each electrode configuration, stimulus levels were tested from 0% to 90% of the dynamic range in nine steps. The effects on consonant and vowel identification were similar. Phoneme identification was usually better for monopolar than for bipolar stimulation. In the lower half of the dynamic range, syllable identification usually increased as a function of stimulus level. In the upper half of the dynamic range, syllable identification continued to increase as a function of level to 90% of the dynamic range for some subjects, while for others there was no appreciable change or a decrease as a function of level. Decreases in performance at high levels were more common with monopolar than bipolar stimulation. These results suggest that if speech processors are programmed to optimize level for each individual, speech perception performance could be improved.

Acoustic Stimulation↗
PubMed2002

A model of a nucleus 24 cochlear implant fitting protocol based on the electrically evoked whole nerve action potential.

OBJECTIVE: The goal of this study was to model a cochlear implant fitting protocol based on the electrically evoked whole nerve action potential (EAP) measured using the Neural Response Telemetry capabilities of the Nucleus C124M cochlear implant. The model and data were based on the significant correlations found between the EAP threshold and growth function slope and psychophysical threshold and, dynamic range, respectively, in 12 subjects (Franck, Reference Note 3; Franck & Norton, 2001). DESIGN: Using a retrospective split-half study design, these correlations found between psychophysical mapping levels and EAP data from six of the subjects were used in a model to predict psychophysical mapping levels from EAP data of the other six subjects. RESULTS: Predicted psychophysical mapping levels from the model of the EAP-based fitting protocol closely approximated measured cochlear implant fitting psychophysics. CONCLUSIONS: The close approximation of the measured data to the model data indicates the feasibility of the clinical use of an EAP-based cochlear implant fitting protocol. The realization of this model would only require two loudness judgments from the patient, whereas traditional fitting requires 44, and would be fit in a live-voice mode, accounting for across-electrode loudness summation.

Auditory Threshold↗
PubMed2002

Effects of Clarion electrode design on mapping levels in children.

The design of the placement of the Clarion cochlear implant's intracochlear electrode array has undergone 2 revisions since its introduction, each to improve modiolar proximity. Stimulation with modiolar proximity may reduce current requirements for threshold levels and most comfortable levels of stimulation. This study analyzed the effects of electrode design on programming levels for deaf children implanted with the 3 cochlear implant designs and followed at The Children's Hospital of Philadelphia. Psychophysical data were reported if measurements were taken approximately 3 months after initial activation, and programming parameters included nonsequential monopolar stimulation of 75-micros-per-phase biphasic pulses presented at 813 Hz per electrode. The threshold level and most comfortable programming level were measured by standard clinical techniques appropriate for children. The results indicate that the 2 electrode placement revisions have each significantly reduced threshold levels and most comfortable stimulation levels. These results are discussed in the context of device aesthetics, safety, and function.

Acoustic Impedance Tests↗
PubMedDate not supplied

Routine use of the crystal device integrity testing system in pediatric patients.

Crystal Device Integrity Testing System (CITS), the first commercially available testing system of its type, allows rapid assessment of cochlear implant function by measuring averaged electrode voltages-the scalp-recorded fields generated by electrode currents. We describe our experience performing routine integrity tests on 44 pediatric cochlear implant patients using the CITS. We present our findings focusing on the monopolar and common ground scans to provide a framework from which CITS scans can be evaluated in the future. We also describe selected cases in which abnormal results using the CITS influenced clinical treatment, demonstrating the utility of performing routine integrity tests.

Child↗