title: Autonomic nervous system responses during sedative infusions of dexmedetomidine.
abstract: BACKGROUND
  The purpose of this study was to determine the effects of dexmedetomidine on systemic and cardiac autonomic reflex responses during rest and during thermal stress.
  
  
  METHODS
  Volunteers received either placebo or low- or high-dose dexmedetomidine (target plasma concentrations 0.3 or 0.6 ng/ml, respectively) infusions in a prospectively randomized, double-blinded crossover study design. After 1 h, baroreflex sensitivity was assessed, and then core body temperature was raised to the sweating threshold and then lowered to the shivering threshold. Plasma catecholamines and blood pressure were measured, and cardiac autonomic responses were assessed by analysis of heart rate variability.
  
  
  RESULTS
  Compared with placebo, plasma norepinephrine concentrations, blood pressure, heart rate, and some heart rate variability measures were lower after 1-h infusion of dexmedetomidine, but baroreflex responses did not differ significantly. Dexmedetomidine blunted the systemic and cardiac sympathetic effects of sweating observed during placebo infusion but had no effect on parasympathetic measures. Increases in blood pressure, and systemic catecholamines due to shivering were observed during placebo and dexmedetomidine, but these responses were less with dexmedetomidine. During shivering, dexmedetomidine infusion was associated with higher low-frequency and high-frequency heart rate variability power but lower heart rate compared with the sweating threshold and with the control period, suggesting nonreciprocal cardiac autonomic responses.
  
  
  CONCLUSIONS
  Infusion of dexmedetomidine results in compensated reductions in systemic sympathetic tone without changes in baroreflex sensitivity. Dexmedetomidine blunts heart rate and the systemic sympathetic activation due to sweating, but it is less effective in blunting cardiac sympathetic responses to shivering. During dexmedetomidine infusion, cardiac sympathetic and parasympathetic tone may have nonreciprocal changes during shivering.
authors.affiliation: Department of Anesthesiology and Cardiovascular Division, Washington University School of Medicine, St. Louis, Missouri 63110, USA. hoguec@notes.wustl.edu
authors.forename: Charles W
authors.initials: CW
authors.lastname: Hogue
authors.forename: Pekka
authors.initials: P
authors.lastname: Talke
authors.forename: Phyllis K
authors.initials: PK
authors.lastname: Stein
authors.forename: Charles
authors.initials: C
authors.lastname: Richardson
authors.forename: Peter P
authors.initials: PP
authors.lastname: Domitrovich
authors.forename: Daniel I
authors.initials: DI
authors.lastname: Sessler
mesh_terms: D000328:Adult; D001341:Autonomic Nervous System / Q000187:drug effects*; D018592:Cross-Over Studies; D020927:Dexmedetomidine / Q000494:pharmacology*; D004311:Double-Blind Method; D004562:Electrocardiography / Q000187:drug effects; D015716:Electrocardiography, Ambulatory; D006339:Heart Rate / Q000187:drug effects; D006358:Hot Temperature / Q000009:adverse effects; D006801:Humans; D006993:Hypnotics and Sedatives / Q000494:pharmacology*; D007262:Infusions, Intravenous; D008297:Male; D011311:Pressoreceptors / Q000187:drug effects; D012018:Reflex / Q000187:drug effects; D015656:Respiratory Mechanics / Q000187:drug effects; D016683:Supine Position / Q000502:physiology
chemical_list: D006993:Hypnotics and Sedatives; D020927:Dexmedetomidine