Graeme Clark Collection
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ItemCochlear implants in children: the value of cochleostomy seals in the prevention of labyrinthitis following pneumococcal otitis media( 1995)Cochlea implantation at an early age is important in rehabilitating profoundly hearing impaired children. Given the incidence of pneumococcal otitis media in young children, there has been concern that cochlear implantation could increase the possibility of otitis media, leading to labyrinthitis in this age group. Clinical experience has not indicated an increase in the frequency of otitis media and labyrinthitis in implanted adults or children over two years. However, labyrinthitis has occurred in implanted animals with otitis media. In order to assess the impact of cochlear implants on the occurrence of labyrinthitis, pneumococcal otitis media was induced in 21 kittens. Thirty-two kitten cochleas were implanted, of which 9 had a fascial graft and 9 a Gelfoam® graft. Nine control cochleas were unimplanted. Labyrinthitis occurred in 44% of unimplanted controls. 50% of implanted ungrafted cochleas, and 6% of implanted grafted cochleas. There was no statistically significant difference between the incidence of labyrinthitis in the implanted cochleas and the unimplanted controls. However there was a statistically significant difference between the ungrafted and grafted cochleas, but not between the two types of graft.
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ItemAcute effects of high-rate stimulation on auditory nerve function in guinea pigs( 1995)Cochlear implants have been shown to successfully provide profoundly deaf patients with auditory cues for speech discrimination. Furthermore, a number of safety studies using the Melbourne/Cochlear electrode array indicated that chronic electrical stimulation using charge-balanced biphasic current pulses and stimulus rates between 100 and 500 pulses per second (pps) do not result in additional spiral ganglion loss or general cochlear pathology.1-3 However, safe maximum levels for stimulus parameters (stimulus rate, charge per phase, charge density) have not yet been adequately defined.
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ItemElectrical stimulation of residual hearing in the implanted cochlea( 1995)The average profoundly deaf person using a cochlear implant can now understand more speech than some severely to profoundly deaf people who use a hearing aid. For this reason there will be an increasing need to consider implanting people with residual hearing. In many of these people there could be significant hearing in the operated ear, as a majority of severely to profoundly deaf people are likely to have a symmetrical hearing loss. When three frequency average hearing thresholds were measured on 219 pensioners from the Australian National Acoustic Laboratories (H. Dillon, unpublished findings), 64% had less than a 10-dB difference between thresholds in each ear.
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ItemCochlear implantation: osteoneogenesis, electrode-tissue impedance, and residual hearing( 1995)This study was undertaken to find out how new bone is produced in the implanted cochlea, and the effects of fibrous tissue and new bone growth on electrode-tissue impedance. This knowledge is essential, as bone and fibrous tissue in the cochlea could account for variations in patients' speech perception performance. The study was also carried out to examine the effects of implantation on residual hearing. This information is also important, as cochlear implant speech perception results in profoundly deaf people are now better on average than severely or profoundly deaf people obtain with a hearing aid. Consequently, more people will need to be considered for cochlear implantation in ears with some residual hearing. In this case we need to know to what extent residual hearing is affected by implantation. (From Introduction)
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ItemEvaluation of a new Spectral Peak coding strategy for the Nucleus 22 channel cochlear implant system( 1994)Sixty-three postlinguistically deaf adults from four English-speaking countries participated in a 17-week field study of performance with a new speech coding strategy, Spectral Peak (SPEAK), and the most widely used strategy, Multipeak (MPEAK), both of which are implemented on wearable speech processors of the Nucleus 22 Channel Cochlear Implant System; MPEAK is a feature-extraction strategy, whereas SPEAK is a filterbank strategy. Subjects' performance was evaluated with an experimental design in which use of each strategy was reversed and replicated (ABAB). Average scores for speech tests presented sound-only at 70 dB SPL were higher with the SPEAK strategy than with the MPEAK strategy. For tests in quiet, mean scores for medial vowels were 74.8 percent versus 70.1 percent; for medial consonants, 68.6 percent versus 56.6 percent; for monosyllabic words, 33.8 percent versus 24.6 percent; and for sentences, 77.5 percent versus 67.4 percent. For tests in noise, mean scores for Four-Choice Spondees at +10 and +5 dB signal-to-noise ratio (S/N) were 88.5 percent versus 73.6 percent and 80.1 percent versus 62.3 percent, respectively; and for sentences at +15 dB, +10, and +5 dB S/N, 66.5 percent versus 43.4 percent, 61.5 percent versus 37.1 percent, and 60.4 percent versus 31.7 percent, respectively. Subjects showed marked improvement in recognition of sentences in noise with the new SPEAK filterbank strategy. These results agree closely with subjects' responses to a questionnaire on which approximately 80 percent reported they heard best with the SPEAK strategy for everyday listening situations.
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ItemPartial hearing loss in the macaque following the co-administration of kanamycin and ethacrynic acid( 1994)Co-administration of kanamycin (KA) with the loop diuretic ethacrynic acid (EA) rapidly produces a profound hearing loss in the cat while maintaining normal renal function [Xu et al., Hear. Res. 70, 205-215 (1993)]. In the present paper we have applied this deafening procedure to the old world monkey Macaca fascicularis (macaque). Following the co-administration of KA and EA, the hearing loss in the macaque developed far slower than we observed in the cat. Moreover, unlike the cat, there was evidence of a partial recovery in the animal’s hearing, resulting in a bilaterally symmetrical high frequency hearing loss. The extent of this hearing loss was dependent on the dose of the EA administered. Finally, the most unexpected result of the present study was the degree of acute nephrotoxicity experienced by these animals following the drug administration. The sensitivity of this species to renal failure restricted the dose of EA that could be safely administered. In conclusion, the co-administration of KA and EA cannot reliably produce a profound hearing loss in the macaque. While it can produce a dose dependent high frequency hearing loss the animal will also experience acute renal failure that requires careful management.
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ItemCochlear implantation in children: labyrinthitis following pneumococcal otitis media in unimplanted and implanted cat cochleas( 1994)Pneumococcal otitis media is frequent in young children and could lead to labyrinthitis post-implantation. To assess the risk and methods of minimizing it by a graft to the round window around the electrode entry point, we have used a cat animal model of pneumococcal otitis media. Twenty-one kittens were used in the study. Thirty-two cochleas were implanted when the kittens were 2 months of age. Fourteen cochleas were implanted without using a graft (12 were available for study); 9 had a fascial graft, and 9 a Gelfoam® graft (7 were available for study). The implanted kittens had their bullae inoculated with Streptococcus pneumoniae 2 months after implantation and were sacrificed 1 week later. There were also 9 unimplanted control ears which were inoculated when the animals were 4 months of age. Labyrinthitis occurred in 44% of unimplanted control, 50% of implanted ungrafted, and 6% of implanted grafted (fascia and Gelfoam®) cochleas. There was no statistically significant difference between the unimplanted control and the implanted cochleas (p < 0.05). There was, however, a difference between the implanted-ungrafted and implanted grafted cochleas, but not between the use of fascia and Gelfoam® to graft the round window entry point. As a result, the data indicates that cochlear implantation does not increase the risk of labyrinthitis following pneumococcal otitis media, but it is desirable to use fascia as a graft to the round window around the electrode entry point.
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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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ItemThe University of Melbourne/Nucleus cochlear prosthesis( 1988)This is a review of research to develop the University of Melbourne/Nucleus cochlear prosthesis for patients with a profound-total hearing loss. A more complete review can be obtained in Clark et al. A prototype receiver-stimulator and multiple-electrode array developed at the University of Melbourne was first implanted in a postlingually deaf adult patient with a profound-total hearing loss on 1 August 1978. A speech processing strategy which could help this patient understand running speech, especially when combined with lipreading was developed in 1978 following initial psychophysical studies. A prototype wearable speech processor was fabricated in 1979, that could provide significant help for the first two patients in understanding running speech when used in combination with lipreading compared with lipreading alone, and it also enabled them to understand some running speech when using electrical stimulation alone. An implantable receiver-stimulator and wearable speech processor embodying the principles of the prototype devices were then produced for clinical trial by the Australian biomedical firm, Nucleus Ltd, and its subsidiaries, Cochlear Pty Ltd and Cochlear Corporation. This cochlear implant was initially clinically trialled on six patients at The Royal Victorian Eye & Ear Hospital in 1982, and shown to give similar results to those obtained with the prototype device. In view of these findings a clinical trial was carried out for a Premarket Approval Application to the US Food and Drug Administration (FDA), and extended to a number of centres in the US, Canada, and West Germany. This clinical trial confirmed that patients could understand running speech when electrical stimulation was combined with lipreading, and that some patients could also understand running speech when using electrical stimulation alone. Today, more than 600 patients world-wide are using cochlear implants developed from the research described in this paper.