Graeme Clark Collection
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ItemCochlear implantation for children: an update [Abstract]( 1992)The performance of the Nucleus 22 channel cochlear implant has been assessed on 142 English speaking children who have worn their device for at least 12 months. The safety of the device has been evaluated on 309 children. A significant improvement for prosody was observed in 66%, for closed-set words in 63% and open-set words in 46%, using electrical stimulation alone. Performance over time increased, especially for open-set speech tests. Prelinguistically deaf children had similar scores to postlinguistically deaf children from prosody and closed-set word tests, but scores were not as good for open-set word tests. Lipreading enhancement was assessed using the CID sentence test, and the mean lipreading-alone score of 51% increased significantly to 71% when lipreading was combined with electrical stimulation. Speech intelligibility was determined with McGarr material and 63% were significantly more intelligible after 12 months' implant experience. There were 6-8% medical/surgical complications compared to 12% for a comparable group of adults. In 2.6% surgical intervention was required and this was primarily for infection or necrosis of the flap.
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ItemFactors predicting postoperative sentence scores in postlinguistically deaf adult cochlear implant patients( 1992)A sample of 64 postlinguistically profoundly to totally deaf adult cochlear implant patients were tested without lipreading by means of the Central Institute for the Deaf (CID) sentence test 3 months postoperatively. Preoperative promontory stimulation results (thresholds, gap detection, and frequency discrimination), age, duration of profound deafness, cause of deafness, lipreading ability, postoperative intracochlear thresholds and dynamic ranges for electrical stimulation, depth of insertion of the electrode array into the scala tympani, and number of electrodes in use were considered as possible factors that might be related to the postoperative sentence scores. A multiple regression analysis with stepwise inclusion of independent variables Indicated that good gap detection and frequency discrimination during preoperative promontory testing, larger numbers of electrodes in use, and greater dynamic ranges for intracochlear electrical stimulation were associated with better CID scores. The CID scores tended to decrease with longer periods of profound deafness.
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ItemThe histopathology of the human temporal bone and auditory central nervous system following cochlear implantation in a patient: correlation with psychophysics and speech perception results( 1988)Cochlear implantation has become a recognised surgical procedure for the management of a profound-total hearing loss, especially in patients who have previously had hearing before going deaf (postlingual deafness). Nevertheless, it is important for progress in the field that patients who have had a cochlear implant, bequeath their temporal bones for research. This will then make it possible to further assess the safety of the procedure, and the factors that are important for its effectiveness. Biological safety has been assessed in a number of studies on animals, in particular, the biocompatibility of the materials used (1,2), the histopathological effects of long-term implantation on the cochlea (3, 4, 5, 6, 7, 8), and the effects of chronic electrical stimulation on the viability of spiral ganglion cells (9, 10, 11, 12). In studying the temporal bones of deceased cochlear implant patients it is possible to help establish that the animal experimental results are applicable to Man. Surgical trauma has been most frequently evaluated by inserting electrodes into cadaver temporal bones. It is important, however, to examine bones that have been previously implanted surgically to ensure that the cadaver findings are applicable to operations on patients. The effectiveness of cochlear implantation can be studied by correlating the histopathological findings, the dendrite and spiral ganglion cell densities, in particular, with the psychophysical and speech perception results. Other benefits also accrue, for example, establishing the accuracy of preoperative X-rays and electrical stimulation of the promontory in predicting cochlear pathology and spiral ganglion cell numbers. For the above reasons it has been especially interesting to examine both the temporal bones and central nervous system from one of our patients (patient 13) who participated in the initial clinical trial of the Cochlear Proprietary Limited (a member of the Nucleus group) multiple-electrode cochlear prosthesis, and who died due to a myocardial infarction following coronary bypass surgery.
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ItemCochlear implantation in children: the risk of pneumococcal otitis media [Abstract]( 1992)Pneumococcal otitis media is most frequent in young children and is a matter of concern in cochlear implantation. In the course of the 'implantation surgery the physiological barrier between the middle ear and inner ear is broken down by incising the round window membrane or by fenestration of the cochlear wall. It is feared that the insertion of an electrode array into the scala tympani could provide a pathway for microorganisms and toxins to enter the cochlea, resulting in labyrinthitis. To assess the actual risk of, secondary inner ear infection post implantation we developed a cat animal model of otitis media. In addition we examined the, effectiveness of different sealing strategies compared to the alternative of leaving the electrode entry point unprotected. For sealing of the cochlea fibrous tissue or gelatine foam was wrapped around the electrode in the round window niche. 22 kittens (44 ears) were used for this study 32, ears were implanted at 2 months of age, and all 44 ears were inoculated after 2 months with a broth of, streptococcus pneumoniae and the animals sacrificed one week later. The bullae of the animals were swabbed and the cochleas processed and examined under light microscopy. Histological analysis of the cochleas showed ,the� highest incidence (45%) of labyrinthine spread of infection in the unimplanted control group. Suppurative or serous labyrinthitis was found in only one third (33.3%) of the implanted and unsealed cochleas. In contrast only one of 16 sealed cochleas, (6.2 %) showed labyrinthine signs of acute inflammation. Experimental pneumococcal otitis media could be reliably established in all animals and proved to be a valuable animal model for the testing of the intracochlear spread of infection. We conclude that a cochlear implant electrode inserted via the round window does not increase the risk of tympanogenic abyrinthitis. Our results indicate that grafting of the electrode entry point results in significant protection of the inner ear against labyrinthine spread of ototis media along the leadwire of the cochlear implant.
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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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