title: Autonomic blockade during sinusoidal baroreflex activation proves sympathetic modulation of cerebral blood flow velocity.
abstract: OBJECTIVE
  Pharmacological blockade showed sympathetic origin of 0.03 to 0.15 Hz blood pressure (BP) oscillations and parasympathetic origin of 0.15 to 0.5 Hz RR-interval (RRI) oscillations, but has not been used to determine origin of cerebral blood flow velocity (CBFV) oscillations at these frequencies. This study evaluated by pharmacological blockade whether 0.1 Hz CBFV oscillations are related to sympathetic and 0.2 Hz CBFV oscillations to parasympathetic modulation.
  
  
  METHODS
  In 11 volunteers (24.6 ± 2.3 years), we monitored RRIs, BP, and proximal middle cerebral artery CBFV, at rest, during 180 s sympathetic BP activation by 0.1 Hz sinusoidal neck suction (NS), and during 180 s parasympathetic RRI activation by 0.2 Hz NS. We repeated recordings after 25 mg carvedilol, and after 0.04 mg/kg atropine. Autoregressive analysis quantified RRI-, BP-, and CBFV-spectral powers at 0.1 Hz and 0.2 Hz. We compared parameters at rest, during 0.1 Hz, or 0.2 Hz NS, with and without carvedilol or atropine (analysis of variance, post hoc testing; significance, P<0.05).
  
  
  RESULTS
  Carvedilol significantly increased RRIs and lowered BP, CBFV, and 0.1 Hz RRI-, BP-, and CBFV-powers at baseline (P=0.041 for CBFV-powers), and during 0.1 Hz NS-induced sympathetic activation (P<0.05). At baseline and during 0.2 Hz NS-induced parasympathetic activation, atropine lowered RRIs and 0.2 Hz RRI-powers, but did not change BP, CBFV, and 0.2 Hz BP- and CBFV-powers.
  
  
  CONCLUSIONS
  Attenuation of both 0.1 Hz CBFV and BP oscillations after carvedilol indicates a direct relation between 0.1 Hz CBFV oscillations and sympathetic modulation. Absent effects of atropine on BP, CBFV, and 0.2 Hz BP and CBFV oscillations suggest that there is no direct parasympathetic influence on 0.2 Hz BP and CBFV modulation.
authors: Department of Neurology, University of Erlangen-Nuremberg, Erlangen, Germany. max.hilz@uk-erlangen.de
authors: Max J
authors: MJ
authors: Hilz
authors: Julia
authors: J
authors: Koehn
authors: Alexandra
authors: A
authors: Tillmann
authors: Stephan
authors: S
authors: Riss
authors: Harald
authors: H
authors: Marthol
authors: Martin
authors: M
authors: Köhrmann
authors: Gerald
authors: G
authors: Wasmeier
authors: Stefan
authors: S
authors: Schwab
authors: Brigitte
authors: B
authors: Stemper
mesh_terms: D000328:Adult; D001285:Atropine / Q000494:pharmacology; D001341:Autonomic Nervous System / Q000502:physiology; D017704:Baroreflex / Q000502:physiology*; D001783:Blood Flow Velocity / Q000502:physiology; D001794:Blood Pressure; D002227:Carbazoles / Q000494:pharmacology; D000077261:Carvedilol; D002560:Cerebrovascular Circulation; D006801:Humans; D008297:Male; D020768:Middle Cerebral Artery / Q000473:pathology; D009991:Oscillometry / Q000379:methods; D010275:Parasympathetic Nervous System / Q000502:physiology; D011412:Propanolamines / Q000494:pharmacology; D012306:Risk; D013564:Sympathetic Nervous System
chemical_list: D002227:Carbazoles; D011412:Propanolamines; D000077261:Carvedilol; D001285:Atropine