title: Lower body negative pressure-induced vagal reaction: role for the osmopressor response?
abstract: BACKGROUND
  Water ingestion elicits an osmopressor response in patients with impaired baroreflexes. In young, healthy subjects, water elicits sympathetic vasoconstriction. This study investigated the effect of water on the lower body negative pressure (LBNP)-induced vasovagal reaction and also analyzed its effect on the change of regional cerebral blood flow during LBNP.
  
  
  METHODS
  Twelve young healthy subjects underwent LBNP (40 mm Hg) tolerance testing for 45 minutes or until presyncopal symptoms occurred. Subjects received either LBNP or no LBNP with or without prior water ingestion. The severity of vasovagal reaction was determined by participant self-report rating of orthostatic symptoms during the LBNP test. Changes of regional cerebral blood flow (rCBF) between LBNP and water ingestion with LBNP groups were assessed using statistical parametrical mapping analyses.
  
  
  RESULTS
  Water ingestion attenuated the severity of symptomatic scores during LBNP (P = 0.004). Water ingestion increased Total peripheral vascular resistance (P < 0.001) and attenuated the blood pressure drop (P < 0.001) at the cessation of study. LBNP decreased rCBF over the left superior prefrontal gyrus, limbic-parahippocampal gyrus, left sublobar-caudate body, and hypothalamus (P < 0.001). Water increased rCBF significantly over the right frontal lobe, including the inferior and medial prefrontal gyrus, subcallosal, and sublobar insula, during LBNP stimulation (P < 0.001).
  
  
  CONCLUSIONS
  Water ingestion strongly reduces symptomatic burden of the vasovagal reaction induced by LBNP stimulation. The cortical activation of limbic and prefrontal cortex likely indicates the involvement of osmopressor response in central autonomic cardiovascular physiology. The central cortical activation of osmopressor response might provide insight into the mechanisms by which water ingestion reduces the vasovagal reaction.
authors: Institute of Aerospace Medicine, National Defense Medical Center, Taipei, Taiwan, Republic of China.
authors: Min-Hui
authors: MH
authors: Li
authors: Pei-Husan
authors: PH
authors: Chen
authors: Shung-Tai
authors: ST
authors: Ho
authors: Che-Se
authors: CS
authors: Tung
authors: Tso-Chou
authors: TC
authors: Lin
authors: Ching-Jiunn
authors: CJ
authors: Tseng
authors: Wen-Sheng
authors: WS
authors: Huang
authors: Chih-Cherng
authors: CC
authors: Lu
mesh_terms: D017704:Baroreflex / Q000502:physiology; D002560:Cerebrovascular Circulation / Q000502:physiology*; D003545:Cysteine / Q000031:analogs & derivatives; D004326:Drinking / Q000502:physiology*; D006801:Humans; D008150:Lower Body Negative Pressure / Q000009:adverse effects*; D008297:Male; D015609:Organotechnetium Compounds; D019462:Syncope, Vasovagal / Q000209:etiology*; D015899:Tomography, Emission-Computed, Single-Photon; D014661:Vasoconstriction; D014882:Water-Electrolyte Balance / Q000502:physiology*; D055815:Young Adult
chemical_list: D015609:Organotechnetium Compounds; C059659:technetium Tc 99m bicisate; D003545:Cysteine