title: Long-term measurement of impedance in chronically implanted depth and subdural electrodes during responsive neurostimulation in humans.
abstract: Long-term stability of the electrode-tissue interface may be required to maintain optimal neural recording with subdural and deep brain implants and to permit appropriate delivery of neuromodulation therapy. Although short-term changes in impedance at the electrode-tissue interface are known to occur, long-term changes in impedance have not previously been examined in detail in humans. To provide further information about short- and long-term impedance changes in chronically implanted electrodes, a dataset from 191 persons with medically intractable epilepsy participating in a trial of an investigational responsive neurostimulation device (the RNS(®) System, NeuroPace, Inc.) was reviewed. Monopolar impedance measurements were available for 391 depth and subdural leads containing a total of 1564 electrodes; measurements were available for median 802 days post-implant (range 28-1634). Although there were statistically significant short-term impedance changes, long-term impedance was stable after one year. Impedances for depth electrodes transiently increased during the third week after lead implantation and impedances for subdural electrodes increased over 12 weeks post-implant, then were stable over the subsequent long-term follow-up. Both depth and subdural electrode impedances demonstrated long-term stability, suggesting that the quality of long-term electrographic recordings (the data used to control responsive brain stimulation) can be maintained over time.
authors.affiliation: Department of Neurological Surgery, University of Wisconsin Hospitals and Clinics, Madison, WI, USA; Department of Biomedical Engineering, University of Wisconsin, Madison, WI, USA. Electronic address: ksillay@gmail.com.
authors.forename: Karl A
authors.initials: KA
authors.lastname: Sillay
authors.forename: Paul
authors.initials: P
authors.lastname: Rutecki
authors.forename: Kathy
authors.initials: K
authors.lastname: Cicora
authors.forename: Greg
authors.initials: G
authors.lastname: Worrell
authors.forename: Joseph
authors.initials: J
authors.lastname: Drazkowski
authors.forename: Jerry J
authors.initials: JJ
authors.lastname: Shih
authors.forename: Ashwini D
authors.initials: AD
authors.lastname: Sharan
authors.forename: Martha J
authors.initials: MJ
authors.lastname: Morrell
authors.forename: Justin
authors.initials: J
authors.lastname: Williams
authors.forename: Brett
authors.initials: B
authors.lastname: Wingeier
mesh_terms: D001921:Brain / Q000502:physiology*; D004311:Double-Blind Method; D017097:Electric Impedance; D004599:Electric Stimulation Therapy / Q000295:instrumentation / Q000379:methods*; D004566:Electrodes; D004827:Epilepsy / Q000628:therapy*; D006801:Humans; D058542:Implantable Neurostimulators
keywords: Current-controlled stimulation; Electrode–tissue interface; Epilepsy; Impedance; Responsive neurostimulation