Graeme Clark Collection
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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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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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ItemBanded intracochlear electrode array: evaluation of insertion trauma in human temporal bones( 1985)A banded free-fit scala tympani array was inserted into a basal turn of nine human cochleas to evaluate the trauma produced by the procedure. These nine cochleas, together with five nonimplanted controls, were serially sectioned and examined microscopically for damage to the membranous labyrinth, in particular the spiral ligament, the basilar and Reissner’s membranes, the stria vascularis, and the osseous spiral lamina. The severity and location of any trauma along the cochlear spiral were recorded. The results indicate that the insertion of the banded scala tympani array resulted in minimal mechanical damage, occurring primarily to a localized region of the spiral ligament. This would not result in significant neural degeneration, and therefore would not compromise the efficacy of multichannel cochlear prosthesis.
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ItemImplanted material tolerance studies for a multiple-channel cochlear prosthesis( 1984)We have performed a number of temporal bone and animal studies in order to evaluate the histopathological effects of intracochlear electrode implantation and chronic electrical stimulation. Our results indicate that (a) the insertion of a free-fit scala tympani array results in minimal damage to the membranous labyrinth; (b) the materials used in the electrode array evoke mild tissue reactions when implanted subcutaneously, in muscle, or within the scala tympani; (c) intracochlear electrical stimulation for periods of 500 to 2000 hours, using carefully controlled biphasic pulses, does not adversely affect the population or neural activity of the primary auditory neurones; (d) labyrinthine infection severely reduces the number of viable spiral ganglion cells; (e) an adequate fibrous tissue seal of the round window can prevent the spread of infection from the bulla to the implanted cochlea in cats, following inoculation of the bulla cavity with bacteria; (f) bone growth is not associated with electrical stimulation per se; (g) the electrode arrays show minimal platinum dissolution and no apparent degradation of the Silastic® carrier following periods of long-term intracochlear electrical stimulation.
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ItemSurgery for an improved multiple-channel cochlear implant( 1984)An improved multiple-channel cochlear implant has been developed. The titanium container with enclosed electronics, the receiver coil and the connector are embedded in medical-grade Silastic. The upper half of the implant has a diameter of 35 mm and a height of 4.5 mm. and the lower half a diameter of 23 mm and a height of.5 mm. The electrode array has also been designed to reduce the possibility of breakage due to repeated movements over many years. The surgery involves drilling a bed in the mastoid bone for the receiver-stimulator, and fixing the proximal electrode under the mastoid cortex. Gentle insertion of the electrode array through the round window and along the seala tympani is achieved with a specially designed microclaw.
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ItemPeri-modiolar electrode arrays: a comparison of electrode position n the human temporal bone(Monduzzi Editore, 1997)This paper describes a radiologic evaluation of three types of peri-modiolar arrays, comparing their trajectory within the scala tympani with a standard Mini-22 electrode. All peri-modiolar arrays were found to lie closer to the modiolus for much of their insertion length compared with the standard array. While one design showed evidence for the potential of increased insertion trauma, two designs produced satisfactory results. Although further electrode development, temporal bone and histopathologic studies arE required, it would appear that the benefits of peri-modiolar electrode arrays will be realised clinically.
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ItemComparison and alternate designs for peri-modiolar electrode arrays: insertion trauma and position [Abstract]( 1997)While it has been shown that the straight but flexible banded electrode array can be safely inserted into the scala tympani of the human cochlea, histological studies have revealed that the array lies along the outer walll.2. Since a profound total hearing loss is generally associated with a moderate to complete degeneration of the spiral ganglion peripheral process, these electrodes lie some distance from their target neural population -the spiral ganglion soma -located within Rosenthal's canal.
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ItemHistopathology following electrode insertion and chronic electrical stimulation(Raven Press, 1985)We have examined a number of safety issues associated with cochlear implants. This work has been primarily designed to evaluate the histopathological effects of intracochlear electrode implantation and chronic electrical stimulation. The results of these studies may be summarized as follows: 1) The insertion of the banded free-fit scala tympani array into human cadaver temporal bones produces minimal damage, occurring primarily to a localized region of the spiral ligament. This damage would not result in significant neural degeneration and thus, would not compromise the efficacy of the multiple channel device; 2) chronic intracochlear electrical stimulation for continuous periods of 500 to 2000 hours, using charge balanced biphasic current pulses developing charge densities of 18-32 }?C/cm2. geom./phase, does not adversely affect the spiral ganglion cell population; 3) labyrinthine infection severely reduces the viable spiral ganglion cell population; 4) the formation of new bone present in approximately half of the animals we have implanted --is not associated with electrical stimulation per se; 5) scanning electron microscope studies of electrodes subjected to long periods of intracochlear electrical stimulation reveals minimal platinum dissolution when compared with unstimulated control electrodes, and electrodes that have been stimulated for similar periods in inorganic saline.