Impedance changes in chronically implanted and stimulated cochlear implant electrodes

Newbold, Carrie; Mergen, Silvana; Richardson, Rachael T.; Seligman, P. M.; Millard, Rodney; Cowan, Robert; Shepherd, Robert K.

doi:10.1179/1754762813y.0000000050

Cited by 69 publications

(66 citation statements)

References 19 publications

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“…Changes in impedance related to the tissue-to-electrode interface and surrounding environment of the cochlea have been reported in several studies [5–8]. In our previous study, we found a significant drop in impedance during initial mapping within 24 hours after cochlear implantation which may have been related to spontaneous recovery of the micro-environment inside the cochlea and a divergence effect of electrical stimulation after the device had been switched on [9].…”

Section: Introductionsupporting

confidence: 51%

Evolution of impedance field telemetry after one day of activation in cochlear implant recipients

Chen

Tsai

et al. 2017

PLoS ONE

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ObjectivesChanges in impedance between 24 hours and one month after cochlear implantation have never been explored due to the inability to switch on within one day. This study examined the effect of early activation (within 24 hours) on the evolution of electrode impedance with the aim of providing information on the tissue-to-electrode interface when electrical stimulation was commenced one day post implantation.MethodsWe performed a retrospective review at a single institution. Patients who received a Nucleus 24RECA implant system (Cochlear, Sydney, Australia) and underwent initial switch-on within 24 hours postoperatively were included. Impedance measurements were obtained intraoperatively and postoperatively at 1 day, 1 week, 4 weeks, and 8 weeks.ResultsA significant drop in impedance was noted 1 day after an initial activation within 24 hours followed by a significant rise in impedance in all channels until 1 week, after which the impedance behaved differently in different segments. Basal and mid-portion electrodes revealed a slight increase while apical electrodes showed a slight decrease in impedance from 1 week to 8 weeks postoperatively. Impedance was relatively stable 4 weeks after surgery.ConclusionsThis is the first study to report the evolution of impedance in all channels between initial mapping 1 day and 1 month after cochlear implantation. The underlying mechanism for the differences in behavior between different segments of the electrode may be associated with the combined effect of dynamics among the interplay of cell cover formation, electrical stimulation, and fibrotic reaction.

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Section: Introductionsupporting

confidence: 51%

Evolution of impedance field telemetry after one day of activation in cochlear implant recipients

Chen

Tsai

et al. 2017

PLoS ONE

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“…This has been studied before both in vivo and in vitro, (14,15) but not at such a high temporal resolution for extended periods of time in a preclinical model. This could potentially lead to improved outcomes for patients as knowledge of temporal changes in the electrodetissue interface and associated safety limitations improves.…”

Section: Discussionmentioning

confidence: 99%

A Flexible Wireless System for Preclinical Evaluation of Retinal Prosthesis

Thien¹,

Millard²,

Epp³

et al. 2018

Sensors and Materials

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In this paper, we present a novel stimulation controller and monitoring system for evaluating the safety and efficacy of implantable neuroprosthetic devices in a preclinical setting. It features a programmable controller designed to be worn in a custom backpack by freely moving feline subjects. A custom controller powered two, modified, 22-channel clinical stimulators simultaneously. The controller and stimulators together weighed 140 g and measured 85 × 70 × 35 mm 3 . Power was supplied from a 3350 mAh lithium-ion battery. A Bluetooth-enabled laptop-PC base station managed up to six systems and allowed the remote adjustment of the stimulation amplitude and automated collection of stimulator telemetry data. The initial application was for the chronic safety testing of a 44-channel retinal prosthesis. Thirteen feline subjects were implanted with a suprachoroidal electrode array, which was then stimulated or monitored continuously for an average of 54.5 d. Batteries were changed twice weekly and electrode impedances were recorded hourly. This allowed broken electrodes and other issues to be quickly identified and addressed. The ability to remotely control the stimulation amplitude minimised the amount of subject handling that was required, likely reducing subject stress. Existing preclinical evaluation systems are either designed for short-term experiments and have many features but limited battery life, or for long-term static stimulation and are long-lived, but with restricted stimulation parameters and channel counts. Here, we have described a system designed to improve the chronic safety testing of electrode arrays. While it was used here with a suprachoroidal retinal implant, it could be readily adapted for other preclinical models requiring continuous, deterministic stimulation over a prolonged period.

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“…Impedance spectroscopy is also suitable for the characterization of DBS electrodes [26] and the encapsulation process of DBS electrodes [33,34]. After implantation, the impedances of DBS [35] or cochlear electrodes [36,37] tend to increase. Typically, the foreign body reaction in rats and, in turn, the electrode impedance stabilize after several weeks [38].…”

Section: Introductionmentioning

confidence: 99%

“…Typically, the foreign body reaction in rats and, in turn, the electrode impedance stabilize after several weeks [38]. This stabilization process has been demonstrated to be perturbed by electrical stimulation in DBS [39] and intra-cochlear electrodes [37,40]. For an optimal adjustment of DBS signals, the kinetics of the resulting electrode-impedance changes by the adventitia formation must be taken into account [41].…”

Section: Introductionmentioning

confidence: 99%

Impedance detection of the electrical resistivity of the wound tissue around deep brain stimulation electrodes permits registration of the encapsulation process in a rat model

Badstuebner

Stubbe

Kroeger

et al. 2017

Journal of Electrical Bioimpedance

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An animal model of deep brain stimulation (DBS) was used in in vivo studies of the encapsulation process of custom-made platinum/iridium microelectrodes in the subthalamic nucleus of hemiparkinsonian rats via electrical impedance spectroscopy. Two electrode types with 100-µm bared tips were used: i) a unipolar electrode with a 200-µm diameter and a subcutaneous gold wire counter electrode and ii) a bipolar electrode with two parallelshifted 125-µm wires. Miniaturized current-controlled pulse generators (130 Hz, 200 µA, 60 µs) enabled chronic DBS of the freely moving animals. A phenomenological electrical model enabled recalculation of the resistivity of the wound tissue around the electrodes from daily in vivo recordings of the electrode impedance over two weeks. In contrast to the commonly used 1 kHz impedance, the resistivity is independent of frequency, electrode properties, and current density. It represents the ionic DC properties of the tissue. Significant resistivity changes were detected with a characteristic decrease at approximately the 2nd day after implantation. The maximum resistivity was reached before electrical stimulation was initiated on the 8th day, which resulted in a decrease in resistivity. Compared with the unipolar electrodes, the bipolar electrodes exhibited an increased sensitivity for the tissue resistivity.

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Impedance changes in chronically implanted and stimulated cochlear implant electrodes

Cited by 69 publications

References 19 publications

Evolution of impedance field telemetry after one day of activation in cochlear implant recipients

Evolution of impedance field telemetry after one day of activation in cochlear implant recipients

A Flexible Wireless System for Preclinical Evaluation of Retinal Prosthesis

Impedance detection of the electrical resistivity of the wound tissue around deep brain stimulation electrodes permits registration of the encapsulation process in a rat model

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