A new perimodiolar electrode array, the curly-with stylet (CwS), has been developed and undergone... more A new perimodiolar electrode array, the curly-with stylet (CwS), has been developed and undergone safety trials in human cadaver temporal bones. The array was developed as a result of animal and modelling studies which indicated that there are potential advantages in situating the electrode array in closer proximity to the neural elements. Preliminary studies with four patients in Melbourne implanted with a developmental pre-curved array had supported the predictions of lower current requirements and possibly more focussed spread of excitation. In this study, the efficacy of positioning and safety of a new perimodiolar array was evaluated. This array was formed to a shape, which was designed to follow, upon release, the curvature of the inner wall of the cochlear, and then held straight for insertion with a central platinum stylet. This was fully removed after electrode insertion into the cochlea. Safety studies, results and the development of an atraumatic insertion technique for t...
Otology & neurotology: official publication of the American Otological Society, American Neurotology Society [and] European Academy of Otology and Neurotology
This is an abstract of a paper from Proceedings of the Australian Neuroscience Society 1999 publi... more This is an abstract of a paper from Proceedings of the Australian Neuroscience Society 1999 published by Australian Neuroscience Society. This version is reproduced with the permission of publisher.
Speech processing strategies based on high rate electrical stimulation have been associated with ... more 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. Six normal hearing cats were bilaterally implanted with a three channel platinum (Pt) scala tympani electrode array and unilaterally stimulated in a monopolar configuration for periods of 600 to 2700 h. A return Pt-electrode was placed outside the bulla. The contralateral cochlea was used as an implanted but unstimulated control. Continuous chronic electrical stimulation at behavioral mid-dynamic range intensities consisted of25 ~s/phase charge-balanced biphasic current pulses delivered at a rate of 4...
A small Platinum (Pt) electrode (geometric area: -0.43 mm) was treated in an electrochemical etch... more A small Platinum (Pt) electrode (geometric area: -0.43 mm) was treated in an electrochemical etching process, to produce a highly porous columnar thin layer (-600 nm) on the surface of the electrode. The modified Pt electrode (Pt-p) showed similar electrical properties to a platinum-black electrode but with high mechanical integrity. Previous studies of chronic stimulation had also shown good biocompatibility and surface stability over several months implantation. This paper discusses the potential applications of the modified electrode as an implanted bio-sensor: (1) as a recording electrode compared to an untreated Pt electrode. (2) as a probe in detecting electrical characteristics of living biological material adjacent to the electrode in vivo, which may correlate to inflammation or trauma repair. Results of electrochemical impedance spectroscopy (BIS) revealed much lower electrode interface polarisation impedance, reduced overall electrode impedance, and a largely constant impe...
Previous experimental studies have shown that chronic electrical stimulation of the auditory nerv... more Previous experimental studies have 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) do not adversely affect the adjacent spiral ganglio~. population. More recently, a number of clinical trials have indicated that speech processing ~trategies based on high pulse rates (1000 pps and more), can further improve speech perception. In this paper we summarize our results following acute and chronic electrical stimulation of the auditory nerve using high pulse rates. We recorded the electrically evoked auditory brainstem response (EABR) before and periodically following two hours of continuous stimulation at rates of 100 1000 pps using intensities at and above the maximmn clinical levels for bipolar scala tympani electrodes. Stimulation at 200, 400 and 1000 pps produced an increasingly significant reduction in the post-stimulus EABR and a decrease in the rate of recovery to prestimulus...
There is clinical interest in the development of high rate speech processing strategies, since th... more There is clinical interest in the development of high rate speech processing strategies, since there are indications that these might enhance speech percep tion due to an improved representation of the rapid variations in amplitude of speech. I Significant improvement in speech perception using high rate stimu lation has been demonstrated in cochlear implant recipients.2•3 However, it is important that the long-term safety of high rate stimulation is clearly estab lished 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.4 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)...
Objectives: To assess the content validity and concurrent validity of a haptically (force feedbac... more Objectives: To assess the content validity and concurrent validity of a haptically (force feedback) rendered, virtual reality simulation of temporal bone surgery.Methods: Eleven naive surgical trainees were given a 1-hour lesson on the operation, cortical mastoidectomy, in the virtual environment with the trainer on a networked simulator and then asked to perform this procedure on a real temporal bone.Results: The simulator was found to be a convincing representation of temporal bone drilling and could be said to exhibit face validity. The simulator was an effective means of teaching both the surgical anatomy and the surgical approach as judged by oral assessments made before and after the virtual reality training session. The trainees were successful in identifying most surgical landmarks during their first temporal bone dissection, and over two thirds found the landmarks at the correct time during the procedure. Some trainees exhibited acceptable or better technique with the drill despite this being their first temporal bone dissection. Subjective assessments indicated a high level of acceptance of simulated surgery for training, and there was perceived value in specific enhancements of the virtual environment that facilitated learning. Particular enhancements of value were the networked simulation, the option to make the model semitransparent to reveal anatomic relationships, and error reporting when the sigmoid sinus or facial nerve was injured.Conclusions: Virtual reality simulation of temporal bone surgery was an effective method for teaching surgical anatomy and planning and was well accepted by trainees.
Protamine reversibly decreases cation permeability and alters the structure of Necturus gallbladd... more Protamine reversibly decreases cation permeability and alters the structure of Necturus gallbladder tight junctions. Conflicting results, however, have been published whether or not it also affects apical cell membrane permeability. We investigated this issue more systematically by measuring voltage (psi mc) and fractional resistance (fRa) of the apical membrane at varying concentrations of protamine, K+, and H+ in the bathing solution. At pH 7.6 and [K+] 2.5 mM, (Poler, M.S. and Reuss, L. (1987) Am. J. Physiol. 253, C662) 6 microM protamine caused psi mc to depolarize from -58 to -51 mV and fRa to decrease from 0.74 to 0.67. If we increased pH to 8.1 these effects were even more pronounced. At [K+] 2.5 mM, but not 4.5 mM, psi mc transiently hyperpolarized for about 5 min after adding protamine. Most importantly, if [K+] was 4.5 mM and pH was adjusted to 7.1 (Bentzel et al. (1987) J. Membr. Biol. 95, 9) no significant changes of psi mc and fRa occurred. In any case, at a supramaximal concentration of 200 microM, protamine did not further increase the paracellular response but produced decreasing psi mc and fRa. We conclude that 6 microM protamine decreases K+ conductance of the apical membrane, if it is already tuned high by high pH. At low control K+ conductance as observed at lower pH, protamine action is restricted to the paracellular pathway. Thus, conflicting results were due to different experimental conditions. At a solution pH of 7.1, 6 microM protamine fulfills criteria of a selective tool for reversibly altering structure and function of the tight junction in Necturus gallbladder.
Biochimica et Biophysica Acta (BBA) - Biomembranes, 1990
Protamine reversibly decreases cation permeability and alters the structure of Necturus gallbladd... more Protamine reversibly decreases cation permeability and alters the structure of Necturus gallbladder tight junctions. Conflicting results, however, have been published whether or not it also affects apical cell membrane permeability. We investigated this issue more systematically by measuring voltage (psi mc) and fractional resistance (fRa) of the apical membrane at varying concentrations of protamine, K+, and H+ in the bathing solution. At pH 7.6 and [K+] 2.5 mM, (Poler, M.S. and Reuss, L. (1987) Am. J. Physiol. 253, C662) 6 microM protamine caused psi mc to depolarize from -58 to -51 mV and fRa to decrease from 0.74 to 0.67. If we increased pH to 8.1 these effects were even more pronounced. At [K+] 2.5 mM, but not 4.5 mM, psi mc transiently hyperpolarized for about 5 min after adding protamine. Most importantly, if [K+] was 4.5 mM and pH was adjusted to 7.1 (Bentzel et al. (1987) J. Membr. Biol. 95, 9) no significant changes of psi mc and fRa occurred. In any case, at a supramaximal concentration of 200 microM, protamine did not further increase the paracellular response but produced decreasing psi mc and fRa. We conclude that 6 microM protamine decreases K+ conductance of the apical membrane, if it is already tuned high by high pH. At low control K+ conductance as observed at lower pH, protamine action is restricted to the paracellular pathway. Thus, conflicting results were due to different experimental conditions. At a solution pH of 7.1, 6 microM protamine fulfills criteria of a selective tool for reversibly altering structure and function of the tight junction in Necturus gallbladder.
A new perimodiolar electrode array, the curly-with stylet (CwS), has been developed and undergone... more A new perimodiolar electrode array, the curly-with stylet (CwS), has been developed and undergone safety trials in human cadaver temporal bones. The array was developed as a result of animal and modelling studies which indicated that there are potential advantages in situating the electrode array in closer proximity to the neural elements. Preliminary studies with four patients in Melbourne implanted with a developmental pre-curved array had supported the predictions of lower current requirements and possibly more focussed spread of excitation. In this study, the efficacy of positioning and safety of a new perimodiolar array was evaluated. This array was formed to a shape, which was designed to follow, upon release, the curvature of the inner wall of the cochlear, and then held straight for insertion with a central platinum stylet. This was fully removed after electrode insertion into the cochlea. Safety studies, results and the development of an atraumatic insertion technique for t...
Otology & neurotology: official publication of the American Otological Society, American Neurotology Society [and] European Academy of Otology and Neurotology
This is an abstract of a paper from Proceedings of the Australian Neuroscience Society 1999 publi... more This is an abstract of a paper from Proceedings of the Australian Neuroscience Society 1999 published by Australian Neuroscience Society. This version is reproduced with the permission of publisher.
Speech processing strategies based on high rate electrical stimulation have been associated with ... more 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. Six normal hearing cats were bilaterally implanted with a three channel platinum (Pt) scala tympani electrode array and unilaterally stimulated in a monopolar configuration for periods of 600 to 2700 h. A return Pt-electrode was placed outside the bulla. The contralateral cochlea was used as an implanted but unstimulated control. Continuous chronic electrical stimulation at behavioral mid-dynamic range intensities consisted of25 ~s/phase charge-balanced biphasic current pulses delivered at a rate of 4...
A small Platinum (Pt) electrode (geometric area: -0.43 mm) was treated in an electrochemical etch... more A small Platinum (Pt) electrode (geometric area: -0.43 mm) was treated in an electrochemical etching process, to produce a highly porous columnar thin layer (-600 nm) on the surface of the electrode. The modified Pt electrode (Pt-p) showed similar electrical properties to a platinum-black electrode but with high mechanical integrity. Previous studies of chronic stimulation had also shown good biocompatibility and surface stability over several months implantation. This paper discusses the potential applications of the modified electrode as an implanted bio-sensor: (1) as a recording electrode compared to an untreated Pt electrode. (2) as a probe in detecting electrical characteristics of living biological material adjacent to the electrode in vivo, which may correlate to inflammation or trauma repair. Results of electrochemical impedance spectroscopy (BIS) revealed much lower electrode interface polarisation impedance, reduced overall electrode impedance, and a largely constant impe...
Previous experimental studies have shown that chronic electrical stimulation of the auditory nerv... more Previous experimental studies have 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) do not adversely affect the adjacent spiral ganglio~. population. More recently, a number of clinical trials have indicated that speech processing ~trategies based on high pulse rates (1000 pps and more), can further improve speech perception. In this paper we summarize our results following acute and chronic electrical stimulation of the auditory nerve using high pulse rates. We recorded the electrically evoked auditory brainstem response (EABR) before and periodically following two hours of continuous stimulation at rates of 100 1000 pps using intensities at and above the maximmn clinical levels for bipolar scala tympani electrodes. Stimulation at 200, 400 and 1000 pps produced an increasingly significant reduction in the post-stimulus EABR and a decrease in the rate of recovery to prestimulus...
There is clinical interest in the development of high rate speech processing strategies, since th... more There is clinical interest in the development of high rate speech processing strategies, since there are indications that these might enhance speech percep tion due to an improved representation of the rapid variations in amplitude of speech. I Significant improvement in speech perception using high rate stimu lation has been demonstrated in cochlear implant recipients.2•3 However, it is important that the long-term safety of high rate stimulation is clearly estab lished 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.4 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)...
Objectives: To assess the content validity and concurrent validity of a haptically (force feedbac... more Objectives: To assess the content validity and concurrent validity of a haptically (force feedback) rendered, virtual reality simulation of temporal bone surgery.Methods: Eleven naive surgical trainees were given a 1-hour lesson on the operation, cortical mastoidectomy, in the virtual environment with the trainer on a networked simulator and then asked to perform this procedure on a real temporal bone.Results: The simulator was found to be a convincing representation of temporal bone drilling and could be said to exhibit face validity. The simulator was an effective means of teaching both the surgical anatomy and the surgical approach as judged by oral assessments made before and after the virtual reality training session. The trainees were successful in identifying most surgical landmarks during their first temporal bone dissection, and over two thirds found the landmarks at the correct time during the procedure. Some trainees exhibited acceptable or better technique with the drill despite this being their first temporal bone dissection. Subjective assessments indicated a high level of acceptance of simulated surgery for training, and there was perceived value in specific enhancements of the virtual environment that facilitated learning. Particular enhancements of value were the networked simulation, the option to make the model semitransparent to reveal anatomic relationships, and error reporting when the sigmoid sinus or facial nerve was injured.Conclusions: Virtual reality simulation of temporal bone surgery was an effective method for teaching surgical anatomy and planning and was well accepted by trainees.
Protamine reversibly decreases cation permeability and alters the structure of Necturus gallbladd... more Protamine reversibly decreases cation permeability and alters the structure of Necturus gallbladder tight junctions. Conflicting results, however, have been published whether or not it also affects apical cell membrane permeability. We investigated this issue more systematically by measuring voltage (psi mc) and fractional resistance (fRa) of the apical membrane at varying concentrations of protamine, K+, and H+ in the bathing solution. At pH 7.6 and [K+] 2.5 mM, (Poler, M.S. and Reuss, L. (1987) Am. J. Physiol. 253, C662) 6 microM protamine caused psi mc to depolarize from -58 to -51 mV and fRa to decrease from 0.74 to 0.67. If we increased pH to 8.1 these effects were even more pronounced. At [K+] 2.5 mM, but not 4.5 mM, psi mc transiently hyperpolarized for about 5 min after adding protamine. Most importantly, if [K+] was 4.5 mM and pH was adjusted to 7.1 (Bentzel et al. (1987) J. Membr. Biol. 95, 9) no significant changes of psi mc and fRa occurred. In any case, at a supramaximal concentration of 200 microM, protamine did not further increase the paracellular response but produced decreasing psi mc and fRa. We conclude that 6 microM protamine decreases K+ conductance of the apical membrane, if it is already tuned high by high pH. At low control K+ conductance as observed at lower pH, protamine action is restricted to the paracellular pathway. Thus, conflicting results were due to different experimental conditions. At a solution pH of 7.1, 6 microM protamine fulfills criteria of a selective tool for reversibly altering structure and function of the tight junction in Necturus gallbladder.
Biochimica et Biophysica Acta (BBA) - Biomembranes, 1990
Protamine reversibly decreases cation permeability and alters the structure of Necturus gallbladd... more Protamine reversibly decreases cation permeability and alters the structure of Necturus gallbladder tight junctions. Conflicting results, however, have been published whether or not it also affects apical cell membrane permeability. We investigated this issue more systematically by measuring voltage (psi mc) and fractional resistance (fRa) of the apical membrane at varying concentrations of protamine, K+, and H+ in the bathing solution. At pH 7.6 and [K+] 2.5 mM, (Poler, M.S. and Reuss, L. (1987) Am. J. Physiol. 253, C662) 6 microM protamine caused psi mc to depolarize from -58 to -51 mV and fRa to decrease from 0.74 to 0.67. If we increased pH to 8.1 these effects were even more pronounced. At [K+] 2.5 mM, but not 4.5 mM, psi mc transiently hyperpolarized for about 5 min after adding protamine. Most importantly, if [K+] was 4.5 mM and pH was adjusted to 7.1 (Bentzel et al. (1987) J. Membr. Biol. 95, 9) no significant changes of psi mc and fRa occurred. In any case, at a supramaximal concentration of 200 microM, protamine did not further increase the paracellular response but produced decreasing psi mc and fRa. We conclude that 6 microM protamine decreases K+ conductance of the apical membrane, if it is already tuned high by high pH. At low control K+ conductance as observed at lower pH, protamine action is restricted to the paracellular pathway. Thus, conflicting results were due to different experimental conditions. At a solution pH of 7.1, 6 microM protamine fulfills criteria of a selective tool for reversibly altering structure and function of the tight junction in Necturus gallbladder.
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