Graeme Clark Collection
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ItemA protocol for the prevention of infection in cochlear implant surgery(Cambridge University Press, 1980)The reduction of infection to an absolute minimum is a very desirable goal in any form of surgery. It is especially important with a cochlear implant operation as infection in the labyrinth can lead to degeneration of the auditory nerve fibres it is hoped to stimulate electrically (Clark et al, 1975). Furthermore, as the implantation of foreign materials increases the risk of infection, as the operation can last 6-7 hours (Altemeier et al., 1976), and as the operators are in very close proximity to the implant site, more stringent measures for the prevention of infection need to be adopted than with other forms of otological surgery. For these reasons a protocol has been developed for preventing infection in our cochlear implant surgery. This is an overall approach to the prevention of infection and involves pre-operative measures, an operating theatre routine, the use of horizontal laminar flow filter units, correct surgical technique and the use of systemic and local antibiotics.
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ItemThe surgery for multiple-electrode cochlear implantations(Cambridge University Press, 1979)The multiple-electrode hearing prosthesis designed in the Departments of Otolaryngology and Electrical Engineering (UMDOLEE) at the University of Melbourne (Clark et al., 1977) has been miniaturized with hybrid circuitry so that, if design changes are necessary as a result of initial patient testing, they can be made at minimal cost. This results, however, in increased package dimensions which makes its placement and the design of the surgery more critical. This problem is increased by the fact that we have considered it important to be able to remove the package and replace it with another without disturbing the implanted electrode array, should the first receiver-stimulator fail or an improved design become available. This has meant the design of a special connector (Patrick, 1977; Clark et al., 1978) which adds to the dimensions of the implanted unit. In addition the placement of the coils for transmitting power and information has to be considered. Not only is it desirable to site the coils at a convenient location behind the ear to facilitate the placement and wearing of the external transmitter, but there should also be no relative movement between the coils and the electronic package. These design considerations have led to the sitting of the coils on top of the hermetically-sealed box, and further increased the height of the package. The dimensions of the package shown in Fig. 1 are length 42 mm, width 32 mm, height of connector 8.5 mm, height of receiver-stimulato unit 13 mm. The surgical considerations discussed are the result of a number of temporal bone and cadaver dissections, and the surgical implantation at The Royal Victorian Eye and Ear Hospital of the UMDOLEE unit in a specially-selected patient.
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ItemA multiple-electrode cochlear implant( 1978)Interest in artificially stimulating the auditory nerve electrically for sensori-neural deafness was first sparked off by Volta in the 18th century. Count Volta, who was the first to develop the electric battery, connected up a number of his batteries to two metal rods which he inserted into his ears. Having placed the rods in his ears he pressed the switch and received "une secousse dans la tete" and perceived a noise like "the boiling of thick soup".
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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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ItemThe development of the Melbourne/Cochlear multiple-channel cochlear implant for profoundly deaf children( 1992)In 1978-79, a speech processing strategy which extracted the voicing (FO) and second formant (F2) frequencies and presented these as rate and place of stimulation respectively to residual auditory nerve fibres was developed for the University of Melbourne's prototype multiple-channel receiver-stimulator (Clark et aI1977, Clark et a11978, Tong et aI1980). This speech processing strategy was shown to provide post linguistically deaf adults with some open-set speech comprehension using electrical stimulation alone, and considerable help when used in combination with lipreading (Clark et al 1981).
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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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ItemSurgical complications with the cochlear multiple-channel intracochlear implant: experience at Hannover and Melbourne( 1991)The surgical complications for the first 153 multi-channel cochlear implant operations carried out at the Medizinische Hochschule in Hannover and the first 100 operations at The University of Melbourne Clinic, The Royal Victorian Eye and Ear Hospital, are presented. In the Hannover experience the major complications were wound breakdown, wound infection, electrode tie erosion through the external auditory canal, electrode slippage, a persistent increase in tinnitus, and facial nerve stimulation. The incidence of wound breakdown requiring removal of the package was 0.6% in Hannover and 1.0% in Melbourne. The complications for the operation at both clinics were at acceptable levels. It was considered that wound breakdown requiring implant removal could be kept to a minimum by making a generous incision and suturing the flap without tension.
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ItemMulti-channel cochlear implants for children: the Melbourne Program( 1991)Although there have been 300 years of deaf education, profoundly-totally deaf children today on average are not able to reach the same level of achievement as their normally hearing peers (Geers & Moog, 1989). This failure of deaf children to develop their true potential is largely due to the difficulty they have in communicating with normally hearing people. During the last 300 years there have been basically two different methods of education used (The New Encyclopaedia Britannica, 1983). Firstly, one which maximises auditory and lip reading cues (auditory/oral), advocated by Juan Pablo Bonet (1620), and one which uses a series of signs to convey meaning (signing), developed by Charles-Michel (1712-89). In addition, there is a method which endeavours to combine both auditory/oral and signing approaches called total communication. In practice, however, children taught by total communication tend to receive speech more predominantly by one or other of these methods.
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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.