Johan H. M. Frijns

Potential distributions and neural excitation patterns in a rotationally symmetric model of the electrically stimulated cochlea

In spite of many satisfactory results, the clinical outcome of cochlear implantation is poorly predictable and further insight into the fundamentals of electrical nerve stimulation in this complex geometry is necessary. For this purpose we developed a rotationally symmetric volume conductor model of the implanted cochlea, using the Boundary Element Method (BEM). This configuration mimics the cochlear anatomy more closely than previous, unrolled models. The calculated potential distribution in the cochlea due to stimulating electrodes is combined with a multiple non-linear node model of auditory nerve fibres, which we recently developed. The combined model is used to compute excitation profiles of the auditory nerve for a variety of stimulus levels and electrode positions. The model predicts that the excitation threshold, the spatial selectivity and the dynamic range depend on the exact position of the electrode in the scala tympani. These results are in good agreement with recently published electrical ABR data. It is shown that the use of actively modelled nerve fibres is essential to obtain correct predictions for the biphasic stimuli typically used in cochlear implants and that unrolling the cochlear duct as done in previous models leads to erroneous predictions regarding modiolar stimulation.

Spatial selectivity in a rotationally symmetric model of the electrically stimulated cochlea

A rotationally symmetric model of electrical stimulation of the guinea pig cochlea with active neural elements is used to study the influence of temporal stimulus parameters and electrode configurations on the spatial selectivity of electrical stimulation by cochlear implants. The width of the excitation patterns is determined with respect to the position of the stimulating electrode pairs in the cochlea. Computed O10 AB values are compared against single fibre data from the cat cochlear nerve as measured by Van den Honert and Stypulkowsky (1987). It turns out that the use of charge-balanced asymmetric rather than symmetric biphasic pulses approximately doubles the number of independent channels that can be applied in a cochlear implant with longitudinal bipolar electrodes, like a configuration with radial electrode pairs using symmetric biphasic pulse stimulation will also do. Finally, the influence on Selectivity of the physiological variation in diameter of the cochlear nerve fibres and of a possible loss of their peripheral processes is studied.

Newborn Hearing Screening vs Later Hearing Screening and Developmental Outcomes in Children With Permanent Childhood Hearing Impairment

CONTEXT Newborn hearing screening programs have been implemented in many countries because it was thought that the earlier permanent childhood hearing impairment is detected, the less developmentally disadvantaged children would become. To date, however, no strong evidence exists for universal introduction of newborn hearing screening. OBJECTIVE To study the effect of newborn hearing screening vs distraction hearing screening, conducted at 9 months of age, on development, spoken communication, and quality of life. DESIGN, SETTING, AND PARTICIPANTS Between 2002 and 2006, all 65 regions in The Netherlands replaced distraction hearing screening with newborn hearing screening. Consequently, the type of hearing screening offered was based on availability at the place and date of birth and was independent of developmental prognoses of individual children. All children born in The Netherlands between 2003 and 2005 were included. At the age of 3 to 5 years, all children with permanent childhood hearing impairment were identified. Evaluation ended December 2009. MAIN OUTCOME MEASURES Performance (education and spoken and signed communication), development (general and language), and quality of life. RESULTS During the study period, 335,560 children were born in a newborn hearing screening region and 234,826 children in a distraction hearing screening region. At follow-up, 263 children in newborn hearing screening regions (0.78 per 1000 children) and 171 children in distraction hearing screening regions (0.73 per 1000 children) had been diagnosed with permanent childhood hearing impairment. Three hundred one children (69.4%) participated in analysis of general performance measures. There was no difference between groups in the primary mode of communication or type of education. Analysis of extensive developmental outcomes included 80 children born in newborn hearing screening regions and 70 in distraction hearing screening regions. Multivariate analysis of variance showed that overall, children in newborn hearing screening regions had higher developmental outcome scores compared with children in distraction hearing screening regions (Wilks λ = 0.79; F(12) = 2.705; P = .003). For social development, the mean between-group difference in quotient points was 8.8 (95% CI, 0.8 to 16.7) and for gross motor development, 9.1 (95% CI, 1.1 to 17.1). For quality of life, the mean between-group difference was 5.3 (95% CI, 1.7 to 8.9), also in favor of children in newborn hearing screening regions. CONCLUSION Compared with distraction hearing screening, a newborn hearing screening program was associated with better developmental outcomes at age 3 to 5 years among children with permanent childhood hearing impairment.

The importance of human cochlear anatomy for the results of modiolus-hugging multichannel cochlear implants.

Hypothesis The fact that the anatomy of the basal turn of the human cochlea, especially, is essentially different from that of other species is likely to influence the outcome of cochlear implantation. Background Multichannel cochlear implants give better speech understanding than single-channel devices. They are intended to make use of the tonotopic organization of the cochlea by selectively stimulating subpopulations of the auditory nerve. At higher stimulus levels and with monopolar stimulation, excitation of nerve fibers from other turns may interfere with this concept, especially with modiolus-hugging electrodes. Methods A three-dimensional spiraling computer model of the human cochlea, based on histologic data, was used to test the spatial selectivity and the dynamic range before cross-turn stimulation takes place for the Clarion HiFocus implant with and without a positioner. The results were compared with a similar model of the guinea pig cochlea. Results In humans (in contrast to the guinea pig), a well-designed modiolus-hugging electrode yielded reduced current thresholds and high spatial selectivity without reduction of the useful dynamic range. The apical turn of the human cochlea, however, is largely comparable in this respect with the guinea pig cochlea, where cross-turn stimulation reduces the dynamic range substantially. Conclusion The clinical success of cochlear implantation in humans and the favorable results with modiolus-hugging devices depend on the anatomy of the human cochlea.

Does Intervention Improve the Natural Course of Glomus Tumors? A Series of 108 Patients Seen in a 32-Year Period

To acquire more insight into the results of treatment versus the “natural” course of glomus tumors, we studied the clinical data of 108 patients, in 58 of whom the disease was hereditary. During a period of 32 years (1956 to 1988), 175 tumors were diagnosed: 52 glomus jugulotympanic tumors, 32 vagal body tumors, and 91 carotid body tumors. The results of radical surgical treatment were disappointing for tumors located at the skull base, ie, nonradical in 59% (n = 23) of the cases, but very good for the carotid body tumors, for which 96% (n = 68) radical excision was achieved. Moreover, surgery at the level of the skull base dramatically increased morbidity, since it frequently induced cranial nerve palsy. During the follow-up period (maximal observation time 32 years, mean 13.5 years) none of the patients died of residual or recurrent tumor or developed distant metastases, irrespective of the mode and outcome of treatment. When these results are combined with the results of pedigree analysis, a realistic approximation of the “natural” course of the disease for both hereditary and nonfamilial tumors can be made. The results raise the question of whether this natural behavior is really improved by intervention. We conclude that removal of carotid body tumors and solitary vagal body tumors should be considered in order to prevent future morbidity. However, for skull base and bilateral glomus tumors a more conservative monitored “wait and see” policy can be sensible and should be considered in any proposal for treatment of head and neck paragangliomas. When there is serious progression of cranial nerve palsy or when intracranial growth becomes life-threatening, surgical intervention cannot be avoided. The main goal of glomus tumor treatment should be to reduce morbidity rather than trying to increase survival rates.

Initial evaluation of the Clarion CII cochlear implant: Speech perception and neural Response imaging

Objective To evaluate the new Clarion® CII cochlear implant with the perimodiolar HiFocus® electrode array, including both speech perception outcomes and the device’s capabilities of measuring the electrically evoked compound action potential (eCAP) of the auditory nerve (Neural Response Imaging, NRI). Design The speech perception scores on CVC words without lip reading were monitored prospectively for the 10 postlingually deaf patients implanted with the Clarion CII device in the period July 2000 until May 2001 in the Leiden University Medical Center. Preoperative and postoperative NRI recordings were made, applying various combinations of monopolar stimulating and recording electrodes with the alternating polarity paradigm available in the test bench software. Results Nine patients preferred the CIS, one the PPS strategy, none the SAS strategy. With their favorite strategy they acquired significant open set speech understanding within a few weeks, resulting in an average CVC phoneme score of 84% (word score 66%) at the end of the study (follow-up 3 to 11 mo). In speech-shaped noise, the average phoneme recognition threshold (PRT) was reached at a signal to noise ratio just below 0 dB. The NRI recordings had clear N1 and P1 peaks if there was at least one contact between the stimulating and recording electrodes, necessitating just 15 sweeps for a reliable recording. We observed considerable inter-patient and inter-electrode variability, but for a given situation NRI input/output curves were stable over time. More apical contacts generally elicited larger eCAPs. Response amplitudes tended to peak at recording sites around apical and basal stimulating electrodes, suggesting a limited spread of excitation. Preliminary recordings with the forward masking paradigm were consistent with the ones with the alternating polarity scheme. Conclusions The Clarion CII is a promising cochlear implant with which our first 10 patients have obtained excellent speech perception results. The NRI system yields high quality signals with a limited number of sweeps at a high sampling rate.

Predictors of Spoken Language Development Following Pediatric Cochlear Implantation

Objectives: Although deaf children with cochlear implants (CIs) are able to develop good language skills, the large variability in outcomes remains a significant concern. The first aim of this study was to evaluate language skills in children with CIs to establish benchmarks. The second aim was to make an estimation of the optimal age at implantation to provide maximal opportunities for the child to achieve good language skills afterward. The third aim was to gain more insight into the causes of variability to set recommendations for optimizing the rehabilitation process of prelingually deaf children with CIs. Design: Receptive and expressive language development of 288 children who received CIs by age five was analyzed in a retrospective multicenter study. Outcome measures were language quotients (LQs) on the Reynell Developmental Language Scales and Schlichting Expressive Language Test at 1, 2, and 3 years after implantation. Independent predictive variables were nine child-related, environmental, and auditory factors. A series of multiple regression analyses determined the amount of variance in expressive and receptive language outcomes attributable to each predictor when controlling for the other variables. Results: Simple linear regressions with age at first fitting and independent samples t tests demonstrated that children implanted before the age of two performed significantly better on all tests than children who were implanted at an older age. The mean LQ was 0.78 with an SD of 0.18. A child with an LQ lower than 0.60 (= 0.78−0.18) within 3 years after implantation was labeled as a weak performer compared with other deaf children implanted before the age of two. Contralateral stimulation with a second CI or a hearing aid and the absence of additional disabilities were related to better language outcomes. The effect of environmental factors, comprising multilingualism, parental involvement, and communication mode increased over time. Three years after implantation, the total multiple regression model accounted for 52% of the variance in receptive language scores and 58% of the variance in expressive language scores. Conclusions: On the basis of language test scores of this large group of children, an LQ of 0.60 or lower was considered a risk criterion for problematic language development compared with other deaf children using CIs. Children attaining LQs below 0.60 should be monitored more closely and perhaps their rehabilitation programs should be reconsidered. Improved language outcomes were related to implantation under the age of two, contralateral stimulation, monolingualism, sufficient involvement of the parents, and oral communication by the parents. The presence of an additional learning disability had a negative influence on language development. Understanding these causes of variation can help clinicians and parents to create the best possible circumstances for children with CIs to acquire language.

Field patterns in a 3D tapered spiral model of the electrically stimulated cochlea.

Despite the fact that cochlear implants are widely and successfully used in clinical practice, relatively little is known to date about the electric field patterns they set up in the cochlea. Based upon the available measurements and modelling results, the scala tympani is usually considered to be a preferential current pathway that acts like a leaky transmission line. Therefore, most authors assume the current thresholds to decay exponentially along the length of the scala tympani. Here we present potential distributions calculated with a fully three-dimensional, spiralling volume conduction model of the guinea pig cochlea, and try to identify its preferential current pathways. The relatively well conducting scala tympani turns out to be the main one indeed, but the exponential decay (J approximately e(-z)) of current is only a good description of the far-field behaviour. In the vicinity of the electrodes, i.e. near the fibres that are most easily excited, higher current densities are found, that are best described by a spherical spread of the current (J approximately 1/R(2)). The results are compared with those obtained with a variant of our previous, rotationally symmetric, model and with measurements in the literature. The implications of the findings are discussed in the light of simulated neural responses.

A quantitative approach to modeling mammalian myelinated nerve fibers for electrical prosthesis design

Presents an upgraded cable model of mammalian myelinated nerve fibers in an extracellularly applied field. The kinetics of the nodes is based upon voltage clamp data in rat motor fibers at 37/spl deg/C (J.R. Schwartz and G. Eikhof, 1987), while the resting membrane potential is computed with the Goldman equation. The resulting spike shape, conduction velocity, strength/duration behavior, and absolute and relative refractory period are in good quantitative agreement with published experimental data in mammals at normal body temperature and at 20/spl deg/C. Results at intermediate temperatures however, suggest that the widely used concept of a constant Q/sub 10/ for the rate constants is invalid. In addition, the model generates realistic abortive spikes towards the end of the absolute refractory period and it can describe the consequences of repetitive firing. The results stress the advantages of a multiple nonlinear node model even if only time aspects of nerve behavior are under study. It turned out, that the model presented here describes in vivo neural properties relevant for electrical prosthesis design better than previous models in literature.<<ETX>>

European multi-centre study of the Nucleus Hybrid L24 cochlear implant

Abstract Objectives: To investigate the preservation of residual hearing in subjects who received the Nucleus Hybrid L24 cochlear implant. To investigate the performance benefits up to one year post-implantation in terms of speech recognition, sound quality, and quality of life. Design: Prospective, with sequential enrolment and within-subject comparisons. Post-operative performance using a Freedom Hybrid sound processor was compared with that of pre-operative hearing aids. Study sample: Sixty-six adult hearing-impaired subjects with bilateral severe-to-profound high frequency hearing loss. Results: Group median increase in air-conduction thresholds in the implanted ear for test frequencies 125–1000 Hz was < 15 dB across the population; both immediately and one year post-operatively. Eighty-eight percent of subjects used the Hybrid processor at one year post-op. Sixty-five percent of subjects had significant gain in speech recognition in quiet, and 73% in noise (≥ 20 percentage points/2 dB SNR). Mean SSQ subscale scores were significantly improved (+ 1.2, + 1.3, + 1.8 points, p < 0.001), as was mean HUI3 score (+ 0.117, p < 0.01). Combining residual hearing with CI gave 22−26 %age points mean benefit in speech recognition scores over CI alone (p < 0.01). Conclusions: Useful residual hearing was conserved in 88% of subjects. Speech perception was significantly improved over preoperative hearing aids, as was sound quality and quality of life.