Graeme Clark Collection

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Author: Shepherd, Robert × End date: 1988 × Start date: 1983 × Type: Journal Article × Subject: electrical stimulation ×

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    Scanning electron microscopy of chronically stimulated platinum intracochlear electrodes
    Shepherd, R. K. ; Murray, M. T. ; Houghton, M. E. ; Clark, Graeme M. ( 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.
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    The histopathological effects of chronic electrical stimulation of the cat cochlea
    Shepherd, R. K. ; Clark, Graeme M. ; Black, R. C. ; Patrick, J. F. (Cambridge University Press, 1983)
    The success of a cochlear implant depends on stimulating an adequate number of viable spiral ganglion cells. The effect of chronic electrical stimulation on ganglion cells is therefore an important consideration when assessing the effectiveness and safety of such a device. The histopathological assessment of chronic unstimulated intracochlear electrodes is now well documented (Simmons, 1967; Clark, 1973; Clark et al, 1975; Schindler and Merzenich, 1974; Schindler, 1976; Schindler et al, 1977; Sutton et al, 1980). These experimental studies have used a variety of electrode designs, materials and surgical techniques. However, all have shown that chronic implantation has little effect on the peripheral nerves and the spiral ganglion cells adjacent to an implant, provided the insertion procedure is free of trauma and infection.
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    Chronic electrical stimulation of the auditory nerve in cats: physiological and histopathological results
    Shepherd, R. K. ; Clark, Graeme M. ; Black, R. C. ( 1983)
    The ability of spiral ganglion cells to survive long-term electrical stimulation is a precondition for the success of cochlear prostheses. In this study 10 cats were implanted bilaterally with bipolar scala tympani electrodes and stimulated for periods of up to 2029 hours using charge balanced biphasic current pulses. The status of the auditory nerve was monitored periodically by recording electrically evoked auditory brainstem responses. At the conclusion of the stimulation program, spiral ganglion cell survival was assessed for stimulated and control cochleas; comparison of the two groups showed no statistically significant difference. The results of this study indicate that long-term intracochlear electrical stimulation using carefully controlled biphasic pulses does not adversely affect the spiral ganglion cell population.