Graeme Clark Collection
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ItemComparison of electrode position in the human cochlea using various perimodiolar electrode arrays( 2000)Objective: This study was conducted to evaluate the insertion properties and intracochlear trajectories of three perimodiolar electrode array designs and to compare these designs with the standard Cochlear /Melbourne array. Background: Advantages to be expected of a perimodiolar electrode array include both a reduction in stimulus thresholds and an increase in dynamic range, resulting in a more localized stimulation pattern of the spiral ganglion cells, reduced power consumption, and, therefore, longer speech processor battery life. Methods: The test arrays were implanted into human temporal bones. Image analysis was performed on a radiograph taken after the insertion. The cochleas were then histologically processed with the electrode array in situ, and the resulting sections were subsequently assessed for position of the electrode array as well as insertion-related intracochlear damage. Results: All perimodiolar electrode arrays were inserted deeper and showed trajectories that were generally closer to the modiolus compared with the standard electrode array. However, although the precurved array designs did not show significant insertion trauma, the method of insertion needed improvement. After insertion of the straight electrode array with positioner, signs of severe insertion trauma in the majority o fimplanted cochleas were found. Conclusions: Although it was possible to position the electrode arrays close to the modiolus, none of the three perimodiolar designs investigated fulfilled satisfactorily all three criteria of being easy, safe, and a traumatic to implant.
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ItemChronic monopolar high rate simulation of the auditory nerve: physiological and histopathological effects(Kugler Publications, 2001)There is clinical interest in the development of high rate speech processing strategies, since there are indications that these might enhance speech perception due to an improved representation of the rapid variations in amplitude of speech. Significant improvement in speech perception using high rate stimulation has been demonstrated in cochlear implant recipients. However, it is important that the long-term safety of high rate stimulation is clearly established prior to its general clinical application. This is especially important, since acute animal studies have shown that high rate stimulation can induce a reduction in the excitability of the auditory nerve. This was also associated with an increase in both threshold and latency of the electrically evoked auditory brainstem response (EABR). However, while a chronic stimulation study indicated that monopolar electrical stimulation of the auditory nerve at rates of 1000 pulses per second (pps)/channel (three channels) had no adverse effects on the spiral ganglion cell density (SGCO),5 there is limited data concerning higher rates. In the present study, we evaluated the electrophysiological and histopathological effects of chronic monopolar electrical stimulation of the auditory nerve using considerably higher stimulus rates than have been used in previous studies.
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ItemPost mortem study of the intracochlear position of the nucleus standard 22 electrode array( 2000)The final position of an intracochlear cochlear implant electrode array can vary depending on the pathology, the insertion technique used and the type of electrode array used. The distance of the electrodes from the target neural elements and the presence of intracochlear fibrous tissue or new bone formation are believed to affect the performance of the device. A post mortem study was conducted to assess these factors.
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ItemPhysiological and histopathological effects of chronic monopolar high rate stimulation on the auditory nerve( 2000)Speech processing strategies based on high rate electrical stimulation have been associated with improvements in speech perception among cochlear implant users. The present study was designed to evaluate the electrophysiological and histopathological effects of long-term intracochlear monopolar stimulation at the maximum stimulus rate of the current Nucleus Cochlear implant system (14493 pulses/s) as part of our ongoing investigations of safety issues associated with cochlear implants