Graeme Clark Collection
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ItemPaediatric cochlear implant surgery [Abstract]( 1992)The operation in children is similar to that in adults, but special care needs to be taken with the skin flap, the anchoring of the electrode array and the sealing of .the cochleostomy. Research into the effects of head growth and otitis media in an implanted ear indicates that these should not be a problem. Surgical complications are also similar to those in adults, with the most common being related to the skin flap. The major complication rate at 4 % is slightly less than that in adults and most of these get effective implant function.
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ItemThe effect of inflammation on blood vessel area as a cause of variation in ganglion cell density measurements in the cat cochlea [Abstract]( 1992)The success of a cochlear implant depends on an adequate number of surviving spiral ganglion cells. Further loss of ganglion cells may arise from the biology of cochlear implantation itself. The quantitative analysis of ganglion cells is, therefore, an important consideration when assessing the biological safety of a cochlear implant.
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ItemMultichannel cochlear implants in children: an overview of experimental and clinical results at the University of Melbourne [Opening Lecture]( 1992)During the last decade there has been great progress in the clinical management of profound, postlinguistically deafened adults through the use of multichannel cochlear implants. The device developed by The University of Melbourne in association with Cochlear Pty Ltd, electrically stimulates selective regions of the auditory nerve using an array of 22 platinum (Pt) electrodes located in the scala tympani. Its development followed basic experimental studies and the development and evaluation of a prototype device in the 1970's. Following safety studies and a successful clinical trial, the Melbourne/Cochlear multichannel implant was approved for use in adults by the United States Food and Drug Administration (FDA) in 1985. More than 3000 patients throughout the world have since been implanted with this device, many being able to understand a significant amount of unfamiliar, connected speech without lipreading Following miniaturization of the implant, it became suitable for use with children. In 1990, after additional biological safety and clinical investigations, the FDA approved the use of the Melbourne/Cochlear multichannel implant for profoundly deaf children above the age of two years. And in 1991, the device received the medical device implantation approval certificate from the Japanese Government. The present paper presents an overview of our recent biological safety studies and clinical experience in children, and discusses the likely future development of these devices.
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ItemFuture developments in speech processing for multichannel cochlear implants in children [Abstract]( 1992)The average speech perception score for adult implant patients is now about 60% on an open-set sentence test without lipreading. This is higher than the scores obtained by many profound and severe-to-profoundly impaired hearing aid users. This suggests that some hearing aid users, particularly those who use a hearing aid in one ear only, could benefit from a cochlear implant. As neither the implant nor the hearing aid will provide perfect speech recognition it is to be expected that this group should obtain maximum benefit by using the hearing aid in one ear together with the implant in the other ear. However, experience with this group of patients has shown that many people find the use of two independent devices unacceptable. Furthermore, perceptual interaction of the acoustic and electrical signals makes it desirable to be able to control the two outputs in a more co-ordinated way than is possible with two independent devices. Consequently, a "bimodal" speech processor has been developed with both acoustic and electrical outputs controlled from the same speech processing unit. Feature coding aspects of the implant processing have been applied to the acoustic signal in such a way as to enhance speech perception with the hearing aid and improve compatibility with the implant. Initial testing with the bimodal aid shows promise to help severely-to-profoundly impaired individuals. The device has also been useful as a research tool to investigate the complex interactions of simultaneous acoustic and electrical stimulation. The Spectral Maxima Sound Processor (SMSP) has also been developed at the University of Melbourne for use with the Nucleus cochlear implant. Studies with adult subjects have shown improved perception of vowels, consonants, words and sentences in quiet and sentences in background noise with the SMSP as compared with the MSP(MULTIPEAK) which is currently supplied for use with this implant. Results for four subjects showed mean scores for open set sentences at a 10 dB signal-to-noise ratio of 78.7% for the SMSP and 50.0% for the MSP. Mean scores for the same group on open set monosyllabic words in quiet were 57.4% for SMSP and 39.9% for MSP. These results suggest that future improvements in speech perception will be possible for children using the Nucleus cochlear implant.
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ItemFactors affecting speech perceptual performance for children using the 22-electrode cochlear prosthesis [Abstract]( 1992)Speech perception results for all 40 children and adolescents implanted with the. Nucleus 22 electrode cochlear prosthesis in Melbourne (as of February 1, 1992) were used to categorize performance for each child into one of six hierarchical groups: 1: detection of speech including high frequencies 2: discrimination of suprasegmental features of speech in addition to 1,3: discrimination and recognition of .vowel sounds in addition to 1 and 2,.4: discrimination arid recognition of consonant sounds in addition to 1, 2 and 3,5: open set speech. recognition with scores less than 20% for unfamiliar material in addition to 1 to 4,6: open set speech recognition with scores greater than 20% for unfamiliar material in addition to 1 to 5, above.All children demonstrated discrimination of suprasegmentals (level 2) and 58% demonstrated some openset speech recognition (levels 5 and 6). The pattern of results suggested that children who can discriminate segmental features of speech tend to achieve open set speech perception after adequate experience with the prosthesis. The performance level, described above, was used as the dependent variable in a multiple regression analysis to assess the effect of various factors on speech perception performance. The duration of profound hearing impairment and the amount of experience with the prosthesis were shown to contribute significantly to the variance, in performance level. A weaker trend was evident (or recently implanted children which may suggest that those' in oral/aural educational settings progress more rapidly, in terms of speech perception, than those in total communication settings. Age at implantation, cause of deafness, hearing levels prior to implantation, and number of electrodes in use, did not contribute significantly. to the variance in speech perception performance for these children. The results showed that all children with less than seven years of profound hearing impairment and with over one year of experience with the prosthesis have achieved some open-set speech recognition. This is an encouraging result as the trend in clinical application of cochlear prostheses has been towards implanting younger children in recent years. If this sample of hearing-impaired children in Melbourne is representative of the general population, we may expect that most implanted young children will ,develop reasonable speech perception skills after adequate experience and training.
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ItemAn antibacterial seal and fixation device for cochlear implants in young children [Abstract]( 1992)Concerns associated with cochlear implantation in young children include intracochlear spread of infection along the electrode array during otitis media, and electrode extraction caused by skull growth post-implantation. New biomaterials were used to seal and secure the electrode at its entry point into the cochlea. Hydroxyapatite was deposited around the outside of an electrode cuff and it bonded well to the surrounding bone of the otic capsule. The electrode cuff accommodated variable insertion depths with the help of a new, silicone based hydroscopic polymer. Preliminary results, including experimental testing of the device in an animal model of pneumococcal otitis media, indicate protection of the implanted cochlea against the spread of infection. Electrode leadwire displacement is prevented by fixation of the array at its entry point This concept may play an important role in the development of a safe cochlear implant design for children under two years of age, who are expected to benefit most from early auditory rehabilitation.
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ItemPsychophysical studies with children using cochlear implants [Abstract]( 1992)Psychophysical studies were conducted on a heterogeneous group of 12 patients using, the Cochlear Nucleus cochlear implant. These patients became profoundly deaf early in life, prior to the full development of auditory and speech skills. The aim of the studies was to determine whether the basic hearing skills of these patients differ from those of patients who becamedeaf later in life. The mean age of, the patients at confirmation of the profound hearing loss was 22.3 months (range 6 to 45 months). The mean age of at the time of implantation as 14.8 years (range 5 to 24 years). The cause of deafness was meningitis for 7 patients, congenital Usher's syndrome for 3 patients and congenital unknown for 2 patients.
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ItemCochlear implantation in young children: studies on head growth, leadwire design and electrode fixation in the monkey model [Abstract]( 1992)For the safety of cochlear implantation in children under two, the implant assembly must not adversely effect the tissue of compromise head growth. Furthermore, growth changes and tissue responses should not impair functioning of the device. Dummy receiver-stimulators, interconnect plugs and leadwire-lengthening systems have been implanted for periods of 40 months in the young monkey to most effectively model the implantation of the young human child. The results show that implanting a receiver-stimulator package has no effect on skull growth or brain tissue under the package. The system for fixing the electrode at the fossa includes proved effective. There was marked osteoneogenesis in the mastoid cavity and this also resulted in fixation of the leadwire outside the cochlea. This study provides evidence for the safety of cochlear implantation in young children.
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ItemCochlear implantation in young children: long-term effects of implantation on the skull and underlying central nervous system tissues in a primate model [Abstract]( 1992)Recent independent studies reporting results obtained by profoundly deaf children implanted with the Melbourne 22-channel cochlear implant have provided further impetus for assessing the feasibility of implanting children under two. Studies in appropriate animal models must first establish the safety of this procedure.
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ItemCochlear implantation in young children: long-term effects of implantation on normal hair cells and spiral ganglion cells in the monkey model [Abstract]( 1992)Recent independent results obtained by profoundly deaf children implanted with the Melbourne 22-channel cochlear implant (1) have provided further impetus. for examining thefeasibility of implanting children under two and children with profound deafness. Safety st1,ldies, in appropriate animal models, must first establish the safety of this procedure.