Biomedical subjects

Jill B Firszt

Publications and source records attributed to Jill B Firszt.

15 recordsLinked to original sources

PubMed2006

Biomechanical strength of reconstruction plates when used for medial support of MED-El cochlear implants: implications for diagnostic MRI.

PURPOSE: It is hypothesized that a mesh reconstruction plate designed to fit a cochlear implant (CI) internal device will provide immediate structural support to the site of the implant and that this strength far exceeds the forces induced by a 1.5-tesla MRI. PROCEDURES: Human calvarial specimens were drilled and plated with reconstruction mesh. Force was applied until failure was reached. RESULTS: Mean maximum force, mean force to first failure and mean displacement measures for group 1 (resorbable mesh, n = 10) were 302.9 N, 283.0 N and 3.05 mm, respectively. The mean maximum force for group 2 (0.4-mm titanium mesh, n = 10) and group 3 (0.6-mm titanium mesh, n = 8), were 121.3 and 234.0 N, respectively. Mean force of first failure was 92.0 N for group 2 and 164.8 N for group 3. CONCLUSIONS: The force required for failure of the mesh is significantly greater than the 0.17 N exerted on a CI magnet by a 1.5-tesla MRI scan.

Absorbable Implants↗

PubMed2006

Differential representation of speech sounds in the human cerebral hemispheres.

Various methods in auditory neuroscience have been used to gain knowledge about the structure and function of the human auditory cortical system. Regardless of method, hemispheric differences are evident in the normal processing of speech sounds. This review article, augmented by the authors' own work, provides evidence that asymmetries exist in both cortical and subcortical structures of the human auditory system. Asymmetries are affected by stimulus type, for example, hemispheric activation patterns have been shown to change from right to left cortex as stimuli change from speech to nonspeech. In addition, the presence of noise has differential effects on the contribution of the two hemispheres. Modifications of typical asymmetric cortical patterns occur when pathology is present, as in hearing loss or tinnitus. We show that in response to speech sounds, individuals with unilateral hearing loss lose the normal asymmetric pattern due to both a decrease in contralateral hemispheric activity and an increase in the ipsilateral hemisphere. These studies demonstrate the utility of modern neuroimaging techniques in functional investigations of the human auditory system. Neuroimaging techniques may provide additional insight as to how the cortical auditory pathways change with experience, including sound deprivation (e.g., hearing loss) and sound experience (e.g., training). Such investigations may explain why some populations appear to be more vulnerable to changes in hemispheric symmetry such as children with learning problems and the elderly.

Acoustic Stimulation↗

PubMed2004

Auditory sensitivity in children using the auditory steady-state response.

OBJECTIVE: To determine the effectiveness of auditory steady-state response (ASSR) as a measure of hearing sensitivity in young children suspect for significant hearing loss. DESIGN: Within-subject comparisons of click auditory brainstem response (ABR) thresholds and ASSR thresholds. SUBJECTS: The study population comprised 42 children suspect for hearing loss and subsequently referred for hearing assessment using electrophysiologic techniques. MAIN OUTCOME MEASURES: Electrophysiologic threshold responses for click ABR and ASSR stimuli (0.5, 1, 2, and 4 kHz) for right and left ears. RESULTS: Based on ABR and ASSR thresholds, 50% of the subjects demonstrated significant hearing loss in the severe to profound range. In some subjects, ASSRs were present at higher stimulus levels when click ABRs were absent. Significant correlations (P<.05) were found between high-frequency ASSR and click ABR thresholds for this study sample. For some subjects, ASSR findings suggested differences between ears that were not observable from the no-response click ABR results. CONCLUSIONS: Auditory steady-state response testing may provide additional information for children who demonstrate hearing levels in the severe to profound range. This information may be helpful when selecting the ear for cochlear implantation for a young hearing-impaired child. Multiple objective methods, such as ABR and ASSR testing, may be needed to determine accurate hearing sensitivity for young children being considered for sensory devices, and in particular, cochlear implants.

Audiometry, Pure-Tone↗

PubMed2004

Electrophysiologic effects of placing cochlear implant electrodes in a perimodiolar position in young children.

OBJECTIVE: The purpose of this study was to intraoperatively record the electrically evoked auditory brainstem response (EABR) before and after placement of the electrode positioning system (EPS) (CII Bionic Ear with HiFocus I cochlear implant electrode array) as well as before and after stylet removal (Nucleus Contour cochlear implant electrode array). It was hypothesized that physiologic changes would occur after perimodiolar positioning of the electrode array and these changes would be evident from the EABR recordings. STUDY DESIGN: Consecutive young (11-36 month old) pediatric cochlear implant recipients (n = 17) had intraoperative EABRs recorded from three intracochlear electrodes that represented apical, medial, and basal locations. Wave V amplitudes and thresholds were studied relative to electrode location and pre- versus postperimodiolar positioning. These evoked potential measures were analyzed for statistical significance. SETTING: Tertiary referral children's hospital/medical college. RESULTS: Wave V thresholds of the EABR were lower, and amplitudes were larger after perimodiolar positioning, although the changes were dependent on electrode location and implant design. Statistically significant decreases in EABR wave V threshold and increases in suprathreshold wave V amplitude were found for the basal electrode for the CII Bionic Ear HiFocus I and for the apical electrode for the Nucleus Contour. CONCLUSIONS: Placement of either the CII Bionic Ear HiFocus I or Nucleus Contour cochlear implant electrode array in the perimodiolar position in young children resulted in less electrical current necessary to stimulate the auditory system. Changes in electrophysiologic thresholds and amplitudes, measured with EABR, indicate that the electrode array is placed closer to the modiolus with both electrode designs.

Child, Preschool↗

PubMed2004

Effect of magnetic resonance imaging on internal magnet strength in Med-El Combi 40+ cochlear implants.

OBJECTIVE: Magnetic resonance imaging (MRI) has been contraindicated when cochlear implants containing an internal magnet are in place because of concerns regarding torque, force, demagnetization, artifacts, induced voltages, and heating. The objective was to determine the magnetic field strength of Med-El Combi 40+ cochlear implant internal magnets after MRI studies. STUDY DESIGN/METHODS: Two fresh cadavers were used to study demagnetization using a repeated measures design and a magnetometer. Pre- and postMRI measurement of magnetic field strength was completed. Five sets of sagittal T1-weighted, axial T1-weighted, and axial T2-weighted sequences were performed on a cadaver at 0.2 Tesla in the device-up and device-down positions. In the other cadaver, 15 sets of sagittal T1-weighted, axial T1-weighted, and axial T2-weighted sequences were performed on a cadaver at 1.5 Tesla were conducted, 5 each with the head oriented at 80, 90, and 100 degrees rotated around the yaw plane (rotated around the z-axis). Subsequently, three cochlear implant patients completed 0.2 Tesla MRIs. For these patients, subjective and objective assessment of cochlear implant performance was performed. SETTING: Academic medical center. RESULTS: In the cadaver studies, analysis of variance showed no significant difference in the magnetic field strength after the 0.2 or 1.5 Tesla scans. There was no significant difference in the magnetic field strength for the three patients undergoing 0.2 Tesla MRIs and no adverse consequences, including no changes in telemetry, auditory sensations, nonauditory sensations, and sound quality. CONCLUSIONS: No significant demagnetization of the internal magnet occurred during repeated 1.5 Tesla MRI scans with the head orientations used in this study. In the cochlear implant patients, no significant demagnetization of the internal magnet occurred after a 0.2 Tesla MRI.

Artifacts↗

PubMed2004

Gamma knife radiosurgery for acoustic neuromas performed by a neurotologist: early experiences and outcomes.

OBJECTIVE: To assess early outcomes after Gamma knife radiosurgery of acoustic neuromas and other skull base tumors. BACKGROUND: Gamma knife radiosurgery is one of the available methods to treat acoustic neuromas, in addition to micro-surgical resection. Neuro-otologists have long been associated with microsurgical resection of these tumors; however, the application of Gamma knife radiosurgery to the treatment of these tumors by neuro-otologists has not been previously described. SETTING: Acoustic Neuroma and Skull Base Surgery Program / Tertiary Referral Center. STUDY DESIGN/PATIENTS/INTERVENTION: Prospective clinical study of all patients treated by the senior author and our gamma knife team beginning in June 2000. MAIN OUTCOME MEASURES: Preoperative MRI, audiometry, vestibular testing and facial nerve electromyography were completed. At six-month intervals postoperatively, audiometry, caloric testing and MRI were performed to determine thresholds and speech discrimination ability, vestibular function, and the size of the tumor. RESULTS: From June 2000 until March 2004, 38 patients were treated, and these included 33 acoustic neuromas, two meningiomas, one glomus jugulare tumor, and two facial neuromas. Greater than 36 month follow-up was available in 7 patients, > 24 months in 24, > 12 months in 31, and > 6 months in 34 patients. Statistically significant reduction in tumor size was seen over time, and tumor control was achieved in all but two patients. Various patterns of changes in auditory function, both in threshold and speech discrimination were observed in either positive or negative directions. CONCLUSIONS: Preliminary experience with Gamma knife radiosurgery indicates that this treatment method represents another option for neuro-otologists to use in managing patients with skull base tumors.

Follow-Up Studies↗

PubMed2004

Recognition of speech presented at soft to loud levels by adult cochlear implant recipients of three cochlear implant systems.

OBJECTIVE: The purpose of this study was to conduct a large-scale investigation with adult recipients of the Clarion, Med-El, and Nucleus cochlear implant systems to (1) determine average scores and ranges of performance for word and sentence stimuli presented at three intensity levels (70, 60, and 50 dB SPL); (2) provide information on the variability of scores for each subject by obtaining test-retest measures for all test conditions; and (3) further evaluate the potential use of lower speech presentation levels (i.e., 60 and/or 50 dB SPL) in cochlear implant candidacy assessment. DESIGN: Seventy-eight adult cochlear implant recipients, 26 with each of the three cochlear implant systems, participated in the study. To ensure that the data collected reflect the range of performance of adult recipients using recent technology for the three implant systems (Clarion HiFocus I or II, Med-El Combi 40+, Nucleus 24M or 24R), a composite range and distribution of consonant-nucleus-consonant (CNC) monosyllabic word scores was determined. Subjects using each device were selected to closely represent this range and distribution of CNC performance. During test sessions, subjects were administered the Hearing in Noise Test (HINT) sentence test and the CNC word test at three presentation levels (70, 60, and 50 dB SPL). HINT sentences also were administered at 60 dB SPL with a signal-to-noise ratio (SNR) of +8 dB. Warble tones were used to determine sound-field threshold levels from 250 to 4000 Hz. Test-retest measures were obtained for each of the speech recognition tests as well as for warble-tone sound-field thresholds. RESULTS: Cochlear implant recipients using the Clarion, Med-El, or Nucleus devices performed on average equally as well at 60 compared with 70 dB SPL when listening for words and sentences. Additionally, subjects had substantial open-set speech perception performance at the softer level of 50 dB SPL for the same stimuli; however, subjects' ability to understand speech was poorer when listening in noise to signals of greater intensity (60 dB SPL + 8 SNR) than when listening to signals presented at a soft presentation level (50 dB SPL) in quiet. A significant correlation was found between sound-field thresholds and speech recognition scores for presentation levels below 70 dB SPL. The results demonstrated a high test-retest reliability with cochlear implant users for these presentation levels and stimuli. Average sound-field thresholds were between 24 and 29 dB HL for frequencies of 250 to 4000 Hz, and results across sessions were essentially the same. CONCLUSIONS: Speech perception measures used with cochlear implant candidates and recipients should reflect the listening challenges that individuals encounter in natural communication situations. These data provide the basis for recommending new candidacy criteria based on speech recognition tests presented at 60 and/or 50 dB SPL, intensity levels that reflect real-life listening, rather than 70 dB SPL.

Adult↗

PubMed2004

Fungal biofilm formation on cochlear implant hardware after antibiotic-induced fungal overgrowth within the middle ear.

Cochlear implantation in patients with chronic suppurative otitis media is managed with perioperative antibiotics; however, fungal overgrowth can occur. We present a child who received oral cefdinir and topical ofloxacin (Floxin). After 6 weeks, a fungal (Candida) biofilm was demonstrated on the implant surface. In this clinical setting, an antimicrobial strategy using an oral antifungal to prevent fungal overgrowth is a possibility.

Anti-Infective Agents↗

PubMed2004

Electrosurgery after cochlear implantation: eighth nerve electrophysiology.

HYPOTHESIS: Monopolar electrosurgery below the neck in cochlear implant recipients can be performed without damage to the internal cochlear stimulator, electrode array, and the cochlear nerve. STUDY DESIGN: Prospective pre- and postintervention electrically evoked compound action potential (ECAP) study of cochlear nerve function and behavioral sound perception assessment. METHODS: Neural response telemetry (NRT) was used to measure ECAPs before and after the use of monopolar electrosurgery during coronary artery bypass surgery to assess prosthetic device function and electrophysiologic function of the cochlear nerve. In addition, electrode voltage impedances and behavioral sound perception was measured at the same time intervals. RESULTS: ECAPs, behavioral sound perception, and electrode voltage impedances were within the normal range, within compliance, and similar preoperatively and on postoperative day 6. CONCLUSION: The studies reported herein were a series of measurements designed to test neural integrity and prosthetic device function before and after the use of monopolar electrosurgery. With appropriate precautions, use of monopolar electrosurgery below the neck in cochlear implant recipients can be performed safely.

Blood Loss, Surgical↗

PubMed2003

Electrically evoked auditory brain stem responses for lateral and medial placement of the Clarion HiFocus electrode.

OBJECTIVE: The purpose of this study was to compare the electrically evoked auditory brain stem response (EABR) for lateral and medial placement of the Clarion HiFocus cochlear implant electrode array via the electrode positioning system (EPS). DESIGN: Twenty-five adult and pediatric cochlear implant recipients participated in the study. Intraoperatively recorded EABRs were evoked by stimuli via three intracochlear electrodes representing apical, medial, and basal locations, and responses were elicited before and after positioner insertion. Evoked potential measures of wave V amplitude and threshold were examined for statistical significance using ANOVA for repeated measures and Chi-Square methods. RESULTS: For a given supra-threshold stimulus level, the increase in EABR wave V amplitude was significantly larger after EPS placement compared to before EPS placement for electrodes 1 (apical) and 13 (basal). Likewise, when the stimulus was decreased to obtain a minimal amplitude, the wave V threshold was significantly lower after EPS placement for electrodes 7 (medial) and 13. The number of measurements that showed decreased wave V threshold after EPS insertion was significantly dependent on intracochlear electrode location. CONCLUSIONS: Placement of the Clarion Electrode Positioning System following HiFocus electrode insertion resulted in a reduction in the electrical current required to activate the auditory system. The effect of the EPS was greatest for the basal location, demonstrated by lower wave V thresholds and a larger percentage increase in wave V amplitude. The EABR reflected electrophysiologic changes relative to lateral-to-medial changes in intracochlear electrode position due to the EPS.

Adult↗

PubMed2002

Neurophysiology of cochlear implant users I: effects of stimulus current level and electrode site on the electrical ABR, MLR, and N1-P2 response.

OBJECTIVE: As the need for objective measures with cochlear implant users increases, it is critical to understand how electrical potentials behave when stimulus parameters are systematically varied. The purpose of this study was to record and evaluate the effects of implanted electrode site and stimulus current level on latency, amplitude, and threshold measures of electrically evoked auditory potentials, representing brainstem and cortical levels of the auditory system. DESIGN: The electrical auditory brainstem response (EABR), electrical auditory middle latency response (EAMLR), and the electrical late auditory response (ELAR) were recorded from the same experimental subjects, 11 adult Clarion cochlear implant users. The Waves II, III, and V of the EABR, the Na-Pa complex of the EAMLR and the N1-P2 complex of the ELAR were investigated relative to electrode site (along the intra-cochlear electrode array) and stimulus current level. Evoked potential measures were examined for statistical significance using analysis of variance (ANOVA) for repeated measures. RESULTS: For the EABR, Wave V latency was significantly longer for the basal electrode (7) compared with the mid (4) and apical (1) electrodes. For the EAMLR and ELAR, there were no significant differences in latency by electrode site. For all subjects and each of the evoked potentials, the apical electrodes tended to have the largest amplitude and the basal electrodes the smallest amplitude, although amplitude differences did not reach statistical significance. In general, decreases in stimulus current level resulted in statistically significant decreases in the amplitude of Wave V, Na-Pa and N1-P2. The evoked potential thresholds for Wave V, Na-Pa, and N1-P2 were significantly higher for the basal Electrode 7 than for Electrodes 4 and 1. CONCLUSIONS: Electrophysiologic responses of Waves II, III, and V of the EABR, Na-Pa of the EAMLR, and N1-P2 of the ELAR were characterized as functions of current level and electrode site. Data from this study may serve as a normative reference for expected latency, amplitude and threshold values for the recording of electrically evoked auditory brainstem and cortical potentials. Responses recorded from cochlear implant users show many similar patterns, yet important distinctions, compared with auditory potentials elicited with acoustic signals.

Adult↗

PubMed2002

Neurophysiology of cochlear implant users II: comparison among speech perception, dynamic range, and physiological measures.

OBJECTIVE: The overall objective of this study was to relate electrically evoked potentials recorded from different levels of the auditory pathway with behavioral measures obtained from adult cochlear implant subjects. The hypothesis was that adult recipients of cochlear implants who have open-set speech perception and those recipients with no open-set speech perception would differ in their neurophysiologic responses recorded at one or more levels of the auditory pathway. DESIGN: The subjects were 11 adults implanted with the Clarion cochlear implant. The electrical auditory brainstem response (EABR, Wave V), electrical auditory middle latency response (EAMLR, Na-Pa complex), and the electrical late auditory response (ELAR, N1-P2 complex), were recorded from three intra-cochlear electrodes. The stimuli used to record the evoked potentials varied in rate and amplitude. Behavioral measures (between threshold and upper limit of comfortable loudness) were used to define the subject's dynamic range at the different stimulus rates. Word and sentence recognition tests evaluated subjects' speech perception in quiet and noise. Evoked potential and behavioral measures were examined for statistical significance using analysis of variance for repeated measures and correlational analyses. RESULTS: Subjects without open-set speech recognition demonstrated 1) poorly formed or absent evoked potential responses, 2) reduced behavioral dynamic ranges, 3) lack of change in the size of the dynamic range with a change in stimulus rate, and 4) longer periods of auditory deprivation. The variables that differentiated the best performers included 1) presence of responses at all three levels of the auditory pathway, with large normalized amplitudes for the EAMLR, 2) lower evoked potential thresholds for the Na-Pa complex, 3) relatively large dynamic ranges, and 4) changes in the size of the dynamic range with changes in stimulus rate. CONCLUSIONS: In this study, the inability to follow changes in the temporal characteristics of the stimulus was associated with poor speech perception performance. Results also illustrate that variability in speech perception scores of cochlear implant recipients relates to neurophysiologic responses at higher cortical levels of the auditory pathway. Presumably, limited neural synchrony for elicitation of electrophysiologic responses underlies limited speech perception. Results confirm that neural encoding with electrical stimulation must provide sufficient physiologic responses of the central nervous system to perceive speech through a cochlear implant.

Adult↗

PubMed2002

A novel connexin 26 compound heterozygous mutation results in deafness.

OBJECTIVE: Mutations of the gap junction beta 2 (GJB2) gene coding for the protein connexin 26 account for up to 50% of nonsyndromic sensorineural hearing loss (NSHL), with specific mutations associated with distinct ethnic groups. A biracial family with nonsyndromic sensorineural deafness consistent with autosomal recessive inheritance was examined for connexin 26 (Cx26) mutations. STUDY DESIGN: Prospective observational study. METHODS: A family consisting of a Caucasian mother and a Chinese father with two of six children affected by NSHL was examined for Cx26 mutations. Peripheral blood lymphocyte DNA was used to amplify by polymerase chain reaction the Cx26 coding region, followed by mutation detection enhancement gel screening and complete sequencing. Phenotypic characterization using audiometric testing was completed for all children and both parents. RESULTS: The two affected children were found to be compound heterozygotes for Cx26 mutations, displaying a previously unreported combination of 35delG and 235delC. The parents were each unaffected heterozygotes consistent with their ethnic heritage, specifically, the Caucasian mother a 35delG heterozygote and the Chinese father a 235delC heterozygote. CONCLUSIONS: Connexin 26 mutations account for a significant proportion of NSHL worldwide, with specific mutations linked to distinct ethnic groups. Genetic analysis of a biracial family with NSHL revealed a novel 35delG/235delC compound heterozygous state in phenotypically affected children. These results highlight the usefulness of Cx26 mutation screening for genetic counseling and suggest that the 235delC mutation is present in China as it is in Japan and Korea.

Adult↗

PubMed2002

Biophysics of cochlear implant/MRI interactions emphasizing bone biomechanical properties.

OBJECTIVE/HYPOTHESIS: The forces exerted during a 1.5-Tesla MRI evaluation on the internal magnet of a cochlear implant (CI) raise concern about the safety for CI recipients. This study determines the magnitude of force required to fracture the floor of a CI receiver bed. METHOD: Recessed CI beds were drilled to maximum uniform thinness into formalin-fixed and fresh-frozen human calvaria specimens. A Med-El stainless steel CI template mounted to the piston of an electrohydraulic testing device was used to fracture the floor of the implant beds. Force and displacement were measured as a function of time using a digital data acquisition system. RESULTS: Mean force to first failure, displacement to first failure, and minimum thickness, respectively, were: group 1 (formalin-fixed, 0.3-0.4-mm thick [n = 22]), 34.08 N (8.21-59.64 N, standard deviation [SD] 15.41 N), 1.09 mm (0.40-2.16 mm, SD 0.51 mm), 0.36 mm (0.3-0.4 mm, SD 0.05 mm); group 2 (formalin-fixed, 0.5-0.9 mm thick [n = 21]), 52.82 N (20.28-135.53 N, SD 25.29 N), 1.08 mm (0.50-2.28 mm, SD 0.47 mm), 0.58 mm (0.5-0.9 mm, SD 0.12 mm); group 3 (fresh-frozen [n = 9]), 134.13 N (86.44-190.70 N, SD 34.92 N), 1.96 mm (1.47-2.46 mm, SD 0.35 mm), 0.42 mm (0.3-0.6 mm, SD 0.11 mm). CONCLUSIONS: The mean magnitude of force required to fracture the floor of a CI bed is significantly greater than those that are generated when a Med-El Combi 40+, CII Bionic Ear CI, or Nucleus Contour CI is placed into a 1.5-Tesla MRI unit.

Adult↗

PubMedDate not supplied

Intensity-dependent activation of the primary auditory cortex in functional magnetic resonance imaging.

PURPOSE: The purpose of this study was to investigate the activation patterns of the primary auditory cortex in response to varying intensities of pure tone stimuli. METHOD: A 1,000-Hz pure tone stimulus was delivered monaurally to the right ear of 12 normal-hearing right-handed volunteers in 20-second on-off cycles. Stimuli were applied at 20 and 50 dB hearing level (HL) above threshold in 12 subjects and at 0, 20, 40, and 50 dB HL above threshold in 6 subjects. Functional magnetic resonance imaging (fMRI) data were obtained using a 1.5-T scanner and echoplanar imaging. Activated pixels were identified in the transverse temporal gyrus (TTG) of both hemispheres in response to pure tone stimuli at each intensity level using cross-correlation analysis (0.6; P < 0.0001). RESULTS: Of the 24 right and left TTGs imaged (n = 12), activation to pure tone stimuli at 20 and 50 dB HL above threshold was seen in 46% and 79% of TTGs, respectively, with bilateral hemispheric activation in 27% and 64% of subjects, respectively. The mean numbers of activated voxels were 4.0 and 13.0, respectively. Of the 12 right and left TTGs imaged at 0, 20, 40, and 50 dB HL above threshold, activation was seen in 33%, 42%, 58%, and 75% of TTGs, respectively. The mean numbers of activated voxels were 5.8, 3.2, 9.8, and 15.3, respectively. There was a nonsignificant trend toward contralateral (left) dominant TTG activation with increased tone intensity. CONCLUSION: Our results show an increased likelihood of TTG activation, increased TTG activation volume, and increased bilateral hemisphere TTG activation with increasing pure tone intensity. Our results suggest that the primary auditory cortex reflects or is directly involved in the central processing of sound intensity and that varying the intensity of even simple stimuli can alter the patterns of fMRI activation in auditory cortex.

Acoustic Stimulation↗