title: Increased pulsatile cerebral blood flow, cerebral vasodilation, and postsyncopal headache in adolescents.
abstract: OBJECTIVE
  We hypothesize that, after a sudden decrease in cerebral blood flow velocity (CBFV) in adolescents, a faint, rapid hyperemic pulsatile CBFV occurs upon the patient's return to the supine position and is associated with postsyncopal headache.
  
  
  METHODS
  This case-control study involved 16 adolescent subjects with a history of fainting and headaches. We induced fainting during 70° tilt-table testing and measured mean arterial pressure, heart rate, end-tidal CO(2), and CBFV. Fifteen control subjects were similarly evaluated with a tilt but did not faint, and comparisons with fainters were made at equivalent defined time points.
  
  
  RESULTS
  Baseline values were similar between the groups. Upon fainting, mean arterial pressure decreased 49% in the patients who fainted vs 6% in controls (P < .001). The heart rate decreased 15% in fainters and increased 35% in controls (P < .001). In patients who fainted, cerebrovascular critical closing pressure increased markedly, which resulted in reduced diastolic (-66%) and mean CBFV (-46%) at faint; systolic CBFV was similar to controls. Pulsatile CBFV (systolic-diastolic CBFV) increased 38% in fainters, which caused flow-mediated dilatation of cerebral vessels. When the fainters returned to the supine position, CBFV exhibited increased systolic and decreased diastolic flows compared with controls (P < .02).
  
  
  CONCLUSIONS
  Increased pulsatile CBFV during and after faint may cause postsyncopal cerebral vasodilation and headache.
authors: Department of Physiology, Center for Hypotension, New York Medical College, Valhalla, NY, USA.
authors: Anthony J
authors: AJ
authors: Ocon
authors: Zachary
authors: Z
authors: Messer
authors: Marvin S
authors: MS
authors: Medow
authors: Julian M
authors: JM
authors: Stewart
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