title: Cerebral hemodynamics and brain functional activity during lower body negative pressure.
abstract: BACKGROUND
  Exposure to high +Gz acceleration forces on a centrifuge or in an aircraft can severely decrease cerebral blood perfusion and cause rapid G-induced loss of consciousness. However, milder acceleration may gradually reduce cerebral blood flow and affect cognitive function in subtler ways. This study used lower body negative pressure (LBNP) to mimic +Gz circulatory effects in order to study cerebral hemodynamics and brain function.
  
  
  METHODS
  Subjects were 15 healthy men, 19-21 yr of age. They were exposed to LBNP at two levels for 5 min each separated by a 10-min recovery period. The conditions were low (LO), -4.00 kPa (-30 mmHg) and high (HI), -6.67 kPa (-50 mmHg).Variables measured before, during, and after LBNP included cerebral blood flow velocity (CBFV) in the middle cerebral artery, blood oxygen saturation (SaO2), heart rate (HR), blood pressure, P300 of event-related EEG potentials, reaction time, and tracking error.
  
  
  RESULTS
  LO significantly reduced CBFV at 4 and 5 min, increased HR, and decreased the amplitude of P300, but none of the other variables changed from baseline. In contrast, HI produced significant changes in most variables: CBFV decreased at 2 min and then fell further at 4 and 5 min, HR increased, and SaO2 decreased. Significant neurocognitive changes included increased latency and reduced amplitude of P300, slower reaction time, and greater tracking error.
  
  
  CONCLUSIONS
  The higher level of LBNP used here reduced cerebral perfusion sufficiently to impair neurocognitive function. This model may be useful for further studies of these and other variables under closely controlled conditions.
authors: Department of Aerospace Medical Equipment, Fourth Military Medical University, Xi'an, China.
authors: Wen-Qiang
authors: WQ
authors: Han
authors: Wen-Dong
authors: WD
authors: Hu
authors: Ming-Qing
authors: MQ
authors: Dong
authors: Zhao-Jun
authors: ZJ
authors: Fu
authors: Zhi-Hong
authors: ZH
authors: Wen
authors: Hong-Wei
authors: HW
authors: Cheng
authors: Jin
authors: J
authors: Ma
authors: Rui-Shan
authors: RS
authors: Ma
mesh_terms: D000337:Aerospace Medicine; D001783:Blood Flow Velocity; D002560:Cerebrovascular Circulation / Q000502:physiology*; D006112:Gravitation; D006439:Hemodynamics / Q000502:physiology*; D006801:Humans; D008150:Lower Body Negative Pressure / Q000009:adverse effects*; D008297:Male; D020768:Middle Cerebral Artery / Q000503:physiopathology*; D011930:Reaction Time; D017585:Ultrasonography, Doppler, Transcranial; D055815:Young Adult