Graeme Clark Collection
Permanent URI for this collection
Search Results
1 - 7 of 7
-
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.
-
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.
-
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.
-
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.
-
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.
-
ItemPhysiological and histopathological response of the cochlea to chronic electrical stimulation of the auditory nerve at high stimulus rates [Abstract]( 1994)Previous research has shown that chronic electrical stimulation of the auditory nerve using charge balanced biphasic current pulses at rates of up to 500 pulses per second (pps) does not adversely affect the adjacent spiral ganglion population. More recently, a number of clinical trials have suggested that speech processing strategies based on high pulse rates (e.g. 1000 pps), can further improve speech perception. In the present study we evaluated the physiological and histopathological response of the cochlea following long-term stimulation using rates of 1000 pps. Thirteen normal hearing cats were bilaterally implanted with scala tympani electrodes and unilaterally stimulated using 25-50 �s per phase charge balanced biphasic current pulses presented at 1000 pps. Additional charge balance was achieved by shorting the electrodes between current pulses. Each animal was stimulated for periods ranging from 700 - 2100 hours at current levels within its dynamic range. Auditory brainstem responses to both acoustic (ABR) and electrical (EABR) stimuli were periodically recorded throughout the chronic stimulation program. At completion of the program the cochleas were prepared for histological examination. While all animals exhibited an increase in acoustic thresholds following surgery, click evoked ABR's returned to near normal levels in half the animals. Frequency specific stimuli indicated that the most extensive hearing loss occurred adjacent to the array (>12 kHz) while lower frequency thresholds appeared at or near normal Our EABR data showed that the majority of animals exhibited slight increases in threshold, although response amplitudes remained very stable for the duration of the stimulus program. The physiological data reported here will be correlated with cochlear histopathology. These initial findings suggest that chronic intracochlear electrical stimulation at high pulse rates, using a carefully designed charge balanced stimulator, does not appear to adversely affect the implanted cochlea.
-
ItemThe histopathology of the human temporal bone following cochlear implantation in a patient: a summary( 1987)The macroscopic and microscopic evaluation of the implanted and unimplanted temporal bones in a patient who had a cochlear prosthesis for 27 months prior to his death from cardiac disease has shown that the device is biocompatible, and does not lead to any significant adverse effects. The cause of deafness was meningitis.