Graeme Clark Collection

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1992 - 1996 4
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Start date: 1990 × End date: 1999 × Subject: otolaryngology × Subject: otology × Author: Shepherd, Robert × Author: Xu, Jin ×

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    Chronic electrical stimulation of the auditory nerve at high rates: I. Effect on residual hearing [Abstract]
    Xu, J. ; Shepherd, R. K. ; Clark, Graeme M. ( 1996)
    In addition to direct excitation of auditory nerve fibres, cochlear implant patients with small amounts of residual hearing may receive important additional auditory cues via electrophonic activation of hair cells 1. Before incorporating electrophonic hearing into speech processing strategies, the extent of hair cell survival following cochlear implantation must first be determined. We have recently demonstrated widespread survival of hair cells apical to electrode arrays implanted for periods of up to three years, the present report describes the effects of chronic electrical stimulation on hair cell survival.
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    Chronic electrical stimulation of the auditory nerve at high rates: II. Cochlear pathophysiology [Abstract]
    Shepherd, R. K. ; Xu, J. ; Clark, Graeme M. ( 1996)
    A major factor in the improved performance of cochlear implant patients has been the use of high stimulus rate speech processing strategies. While these strategies show clear clinical advantage, we know little of their long-term safety. Indeed, recent studies have indicated that high stimulus rates at intensities above clinical limits, can result in neural damage as a result of prolonged neuronal hyperactivity. The present study was designed to evaluate the effects of chronic electrical stimulation of the auditory nerve at high rates, using intensities within clinical limits.
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    Cochlear implants: high rate stimulation studies and the effect of electrode position [Abstract]
    Shepherd, R. K. ; Huang, C. Q. ; Xu, J. ; Tykocinski, M. ; Seligman, P. M. ; Clark, Graeme M. ( 1996)
    This paper summarizes our recent findings investigating the safety of high rate electrical stimulation, and reviews the effects of electrode position on auditory excitability. These studies used charge balanced biphasic pulses and electrode shorting between stimuli to minimize any residual charge or direct current. High rate (400-1000 pulses/s) electrical stimulation of the auditory nerve can result in significant stimulus induced reductions in auditory nerve excitability at stimulus levels well above those used clinically (1). The extent of this reduction was dependent on stimulus rate, intensity and duty cycle, implying that such changes were related to the degree of evoked activity.
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    Cochlear implantation in young children: studies on head growth, leadwire design and electrode fixation in the monkey model [Abstract]
    Burton, Martin J. ; Xu, J. ; Shepherd, R. K. ; Xu, S-A. ; Seldon, H. L. ; Franz, B. K-H. G. ; Clark, Graeme M. ( 1992)
    For the safety of cochlear implantation in children under two, the implant assembly must not adversely effect the tissue of compromise head growth. Furthermore, growth changes and tissue responses should not impair functioning of the device. Dummy receiver-stimulators, interconnect plugs and leadwire-lengthening systems have been implanted for periods of 40 months in the young monkey to most effectively model the implantation of the young human child. The results show that implanting a receiver-stimulator package has no effect on skull growth or brain tissue under the package. The system for fixing the electrode at the fossa includes proved effective. There was marked osteoneogenesis in the mastoid cavity and this also resulted in fixation of the leadwire outside the cochlea. This study provides evidence for the safety of cochlear implantation in young children.