Graeme Clark Collection
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ItemThe biologic safety of the Cochlear Corporation multiple-electrode intracochlear implant( 1988)Studies have been undertaken to confirm the biologic safety of the Cochlear Corporation multi-electrode intracochlear implant. The materials used are biocompatible. The electrode array is flexible: it can be inserted with minimal or no trauma, providing the insertion is stopped when resistance is first felt. An atraumatic insertion is facilitated if a good view is obtained along the scala tympani of the basal turn of the cochlea by drilling through the crista fenestrae. The passage of the electrode around the cochlea can be facilitated if the electrode is rotated during insertion (clockwise for the left and anticlockwise for the right cochlea). The electrode can be explanted and another one reinserted with minimal or no trauma. A seal established around the electrode after an implantation period of 2 weeks can prevent infection extending from the middle to the inner ear. The electrical stimulus parameters produced by the Nucleus receiver-stimulator cause no loss of spiral ganglion cells or corrosion of the platinum band electrodes. Long-term stimulation has been carried out for up to 8 years in patients without affecting their clinical performance.
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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.
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ItemEffect of high electrical stimulus intensities on the auditory nerve using brain stem response and audiometry( 1987)The response of the auditory nerve to acute intracochlear electrical stimulation using charge-balanced biphasic current pulses was monitored using electrically evoked auditory brain stem responses (EABRs). Stimulation at moderate charge densities (64 µC cm-2 geom/ phase; 0.8 mA, 200 µs/phase) for periods of up to 12 hours produced only minimal short-term changes in the EABR. Stimulation at a high charge density (144 µC cm-2 geom/phase; 1.8 mA, 200 µs/phase) resulted in permanent reductions in the EABR for high stimulus rates (> 200 pulses per second [pps]) or long stimulus durations (12 hours). At lower stimulus rates and durations, recovery to prestimulus levels was slow but complete. The mechanisms underlying these temporary and permanent reductions in the EABR are probably caused by neural adaptation and more long-term metabolic effects. These findings have implications for the design of speech-processing strategies using high stimulus rates.
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ItemResponses of cat auditory nerve fibers to biphasic electrical current pulses( 1987)Discharge patterns of single auditory nerve fibers were recorded from normal-hearing cats implanted with a I2-band intracochlear electrode array. Stimuli were biphasic current pulses of specifiable width, amplitude, and rate. Acoustic tuning curves were obtained to determine the cochlear positions of the fibers. Response latencies to electrical stimuli formed two groups. Short latency (0.3 to 0.7 ms) responses were attributed to direct activation of spiral ganglion neurons. At high stirnulus intensities, these often exhibited abrupt shifts toward even shorter latencies. Long latency (> 1.5 ms) responses were probably caused by electrophonic activation of functional hair cells. Response thresholds to electrical stimuli depended on a fiber's proximity to the stimulating electrodes, and they did not depend on a fiber's acoustic response threshold or spontaneous discharge rate. High intensity (> 1.5 mA) stimuli could excite fibers over a wide range of characteristic frequencies, even for the narrowest (0.45 mm) electrode separations. Response threshold was an exponentially decreasing function of pulse width for widths up to 300µs/phase. Fiber discharges were highly phase-locked at all suprathreshold intensities, and saturation discharge rates usually equaled stimulus pulse rates for rates up to at least 800 pulses/s. Dynamic ranges were small (I to 6 dB), increased with pulse rate, and were uncorrelated with electrical response threshold. Within the dynamic range, shapes of poststimulus time and interspike interval histograms resembled those obtained in response to acoustic stimuli. Depolarization block caused fiber activity to cease in 2 to 5 seconds for sustained stimuli presented at high (> 600 pulses/s) pulse rates and intensities.
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ItemMiddle ear infection postimplantation: response of the round window membrane to Streptococcus pyogenes( 1987)The seal of the implanted round window membrane to resist Streptococcus pyogenes invasion from the middle ear was investigated in 12 cats. Results showed that the implanted round window membrane is able to form a barrier for S pyogenes starting 1 week postimplantation. Under normal conditions S pyogenes did not pass through the round window membrane, nor through the gap that existed between the membrane and the prosthesis. Mechanical disruption of the round window seal, however, and severe inflammatory response to S pyogenes caused the infection to extend into the inner ear.
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ItemSurgery for the safe insertion and reinsertion of the banded electrode array( 1987)Adhering to the surgical technique outlined in the protocol for the Nucleus implant has resulted in over 100 patients worldwide obtaining significant benefit from multichannel stimulation. A detailed analysis of the results in 40 patients shows that it improves their awareness of environmental sounds and their abilities in understanding running speech when combined with lipreading. In addition, one third to one half of the patients also understand significant amounts of running speech without lipreading and some can have interactive conversations over the telephone. It is clear that any insertion trauma is not significant, which is confirmed by the excellent clinical results.
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ItemA multiple-electrode intracochlear implant for children( 1987)A multiple-electrode intracochlear implant that provides 21 stimulus channels has been designed for use in young children. It is smaller than the adult version and has magnets to facilitate the attachment of the headset. It has been implanted in two children aged 5 and 10 years. The two children both lost hearing in their third year, when they were still learning language. Following implantation, it was possible to determine threshold and comfortable listening levels for each electrode pair. This was facilitated in the younger child by prior training in scaling visual and electrotactile stimuli. Both children are regular users of the implant, and a training and assessment program has been commenced.
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ItemPneumococcal middle ear infection and cochlear implantation( 1987)A limited study for the experimental induction of pneumococcal otitis media is presented. It is a useful model to study the effects of otitis media in the implanted and nonimplanted cochlea of the cat. Pneumococcal otitis media caused minor pathological changes in two nonimplanted cochleas and more widespread changes together with significant loss of neural elements in two implanted cochleas. However, the small number of animals used in this study did not allow us to distinguish between the effects of electrode insertion trauma, infection, or the combination of both.
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ItemScanning electron microscopy of chronically stimulated platinum intracochlear electrodes( 1985)Platinum electrodes were examined for evidence of corrosion using a scanning electron microscope (SEM). In vivo electrodes stimulated using charge-balanced biphasic pulses for periods of up to 2000 h at charge densities of 0.18-0.32 µC mm-2 geom. per phase, were compared with in vitro electrodes stimulated in inorganic saline using similar stimulus parameters, and with in vivo control electrodes. The in vitro stimulated electrodes showed evidence of platinum corrosion at high charge density and aggregate charge injection. Significantly, the in vivo stimulated electrodes showed no evidence of stimulus induced corrosion. Indeed, their surfaces were similar to the in vivo control electrodes. In vitro electrochemical studies have demonstrated that proteins play a significant role in the inhibition of platinum dissolution: the present study has demonstrated an inhibitory effect in vivo. This may be due to the presence of proteins.