Graeme Clark Collection

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1997 - 1998 2
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Author: Clark, Graeme × Author: Huang, Christie × Author: Shepherd, Robert × End date: 1998 × Start date: 1997 × Subject: cochlear implants × Subject: otolaryngology ×

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    Direct current measurements in cochlear implants: an in vivo and in vitro study
    Huang, Christie Q. ; Carter, Paul M. ; Shepherd, Robert K. ; Seligman, Peter M. ; Tabor, Bruce ; Clark, Graeme M. ( 1998)
    Direct current (DC) was measured both in vivo and in vitro in cochlear implant electrodes with stimulation at moderate to high pulse rates in monopolar and bipolar modes. In vivo DC was approximately 2-3 times higher than that measured in vitro. In vivo DC levels were <100 nA even at very high rates, although DC levels increased as a function of stimulus rate and charge intensity. DC levels were lower: in the monopolar than in the bipolar stimulation condition. Stimulation with a monopolar capacitively coupled extracochlear electrode showed even lower DC levels in the intracochlear .electrodes. Our results indicated that the Nucleus electrode shorting system is able to maintain a low level of DC during very high rate stimulation for both monopolar and bipolar modes.
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    Electrical stimulus induced changes in excitability of the auditory nerve
    Huang, C. O. ; Shepherd, Robert K. ; Seligman, P. M. ; Clark, Graeme M. ( 1997)
    High rate electrical stimulation of the auditory nerve using stimulus intensities well above the clinical limits can induce a significant reduction in the excitability of the auditory nerve as measured by a decrement in the amplitude of the electrically evoked auditory brainstem response (EABR). Two potential mechanisms may be associated with this stimulus induced reduction in activity: 1) stimulus induced prolonged neuronal hyperactivity; and 2) the generation of adverse electrochemical productions from the electrode surface. The purpose of the present study was to assess the extent to which adverse electrochemical damage contributes to the stimulus induced reduction in auditory nerve excitability. Twenty-six adult guinea pigs anaesthetized with ketamine (40 mg/kg i.p.) and xylazine (4 mglkg i.p.), were bilaterally implanted and unilaterally stimulated for two hours using a stimulus intensity of two or four times EABR threshold. Stimulus rates of 200, 400, or 1000 pulses/s (pps) were delivered via a standard platinum scala tympani electrode or large surface area ("high Q") platinum electrode.