title: Adrenergic and vagal baroreflex sensitivity in autonomic failure.
abstract: BACKGROUND
  The baroreflex is responsible for maintaining a stable blood pressure (BP) despite changes in body positions and fails in many autonomic disorders. The baroreflex regulates BP by changing the heart rate (vagal component) and total peripheral resistance (adrenergic component). Baroreflex sensitivity is widely used to quantify the vagal component of the reflex, but the adrenergic component is not quantifiable in the autonomic laboratory.
  
  
  OBJECTIVE
  To develop and validate an index of adrenergic baroreflex sensitivity.
  
  
  METHODS
  We validated this index with microneurographically recorded muscle sympathetic nerve discharges generated by the Valsalva maneuver and verified it against groups of patients with graded severities of adrenergic failure.
  
  
  RESULTS
  Adrenergic baroreflex sensitivity relates BP recovery time to the preceding decrease in BP evoked by the Valsalva maneuver. This index showed a graded and highly significant impairment in 3 groups of patients, (1) those with orthostatic hypotension (n = 26), (2) those with borderline orthostatic hypotension (n = 34), and (3) those with impaired reflex vasoconstriction without orthostatic BP change (n = 24), when compared with an age- and sex-matched control group (n = 29). Adrenergic baroreflex sensitivity better tracked the severity of adrenergic failure than the vagal component of baroreflex sensitivity and provides a much needed index to quantify total peripheral resistance changes in patients with adrenergic failure.
  
  
  CONCLUSIONS
  The 2 indices of baroreflex sensitivity separately evaluate the vagal and adrenergic components of the baroreflex. Combined, they provide an index of composite or global baroreflex function.
authors.affiliation: Department of Neurology, Mayo Foundation, Rochester, MN 55905, USA.
authors.forename: Christine
authors.initials: C
authors.lastname: Schrezenmaier
authors.forename: Wolfgang
authors.initials: W
authors.lastname: Singer
authors.forename: Nicolette Muenter
authors.initials: NM
authors.lastname: Swift
authors.forename: David
authors.initials: D
authors.lastname: Sletten
authors.forename: James
authors.initials: J
authors.lastname: Tanabe
authors.forename: Phillip A
authors.initials: PA
authors.lastname: Low
mesh_terms: D000328:Adult; D000368:Aged; D001342:Autonomic Nervous System Diseases / Q000503:physiopathology*; D017704:Baroreflex / Q000502:physiology*; D001794:Blood Pressure / Q000502:physiology; D016022:Case-Control Studies; D005260:Female; D006339:Heart Rate / Q000502:physiology; D006801:Humans; D008297:Male; D008875:Middle Aged; D012680:Sensitivity and Specificity; D013564:Sympathetic Nervous System / Q000503:physiopathology*; D014630:Vagus Nerve / Q000503:physiopathology*; D014636:Valsalva Maneuver / Q000502:physiology