title: Longitudinal impedance variability in patients with chronically implanted DBS devices.
abstract: BACKGROUND
  Deep brain stimulation (DBS) is an effective therapy for advanced movement disorders, but its optimal use is still controversial. One factor that could play a role in the proper delivery of therapeutic stimulation by current DBS devices is the variability of the impedance at the interface between the electrode surface and surrounding tissue.
  
  
  OBJECTIVE
  To analyze variability and trends in the impedance of chronically-implanted DBS electrodes in subjects with movement disorders.
  
  
  METHODS
  We reviewed impedance values from medical records of DBS patients at an academic tertiary-care movement disorders center. The standard deviation of data recorded within individual subjects and single contacts were used as measures of longitudinal impedance variability. A generalized linear mixed model (GLMM) determined if a number of effects had significant influences on impedance.
  
  
  RESULTS
  We analyzed 2863 impedance measurements from 94 subjects. Median variability, for subjects with follow-up from 6 months to 5 years (n = 77), was 194 Ω for individual subjects and 141 Ω for individual contacts, with a range spanning from 18 to over 600 Ω. The GLMM, incorporating all subjects (n = 94), identified time, electrical activity, implanted target, contact position on the electrode and side of implantation as significant predictors of impedance. Age and disease duration at surgery, gender or ethnicity were not significant predictors.
  
  
  CONCLUSIONS
  Our analysis suggests that a significant amount of impedance variability can be expected in chronically implanted DBS electrodes and indicates a number of factors with possible predictive value. Further studies are needed to link impedance characteristics to clinical outcomes.
authors.affiliation: Department of Neurology, Cedars-Sinai Medical Center, 8730 Alden Drive, Thalians E-238, Los Angeles, CA 90048, USA.
authors.forename: Tyler
authors.initials: T
authors.lastname: Cheung
authors.forename: Miriam
authors.initials: M
authors.lastname: Nuño
authors.forename: Matilde
authors.initials: M
authors.lastname: Hoffman
authors.forename: Maya
authors.initials: M
authors.lastname: Katz
authors.forename: Camilla
authors.initials: C
authors.lastname: Kilbane
authors.forename: Ron
authors.initials: R
authors.lastname: Alterman
authors.forename: Michele
authors.initials: M
authors.lastname: Tagliati
mesh_terms: D000328:Adult; D001921:Brain / Q000502:physiology; D046690:Deep Brain Stimulation / Q000295:instrumentation / Q000379:methods*; D017097:Electric Impedance; D005260:Female; D006801:Humans; D058542:Implantable Neurostimulators; D008297:Male; D009069:Movement Disorders / Q000628:therapy*; D015203:Reproducibility of Results; D012189:Retrospective Studies
keywords: Deep brain stimulation; Globus pallidus; Impedance; Movement disorders; Subthalamic nucleus