title: Regional cerebral blood flow during acute hypoxia in individuals susceptible to acute mountain sickness.
abstract: Individuals susceptible to high altitude pulmonary edema show altered pulmonary vascular responses within minutes of exposure to hypoxia. We hypothesized that a similar acute-phase vulnerability to hypoxia may exist in the brain of individuals susceptible to acute mountain sickness (AMS). In established AMS and high altitude cerebral edema, there is a propensity for vasogenic white matter edema. We therefore hypothesized that increased cerebral blood flow (CBF) during acute hypoxia would also be disproportionately greater in white matter (WM) than grey matter (GM) in AMS-susceptible subjects. We quantified regional CBF using arterial spin labeling MRI during 30 min hypoxia (F(I)O(2) = 0.125) in two groups: AMS-susceptible (AMS-S, n = 6) who invariably experienced AMS at altitude, and AMS-resistant (AMS-R, n = 6) who never experienced AMS despite multiple rapid ascents to high altitude. SaO(2) during hypoxia did not differ between groups (AMS-S = 87+/-4%, AMS-R = 89+/-3%, p = 0.3). Steady-state whole-brain CBF increased in hypoxia (p<0.005), but did not differ between groups (normoxia: AMS-S = 42.7+/-14.0 ml/(100 g min), AMS-R = 41.7+/-10.1 ml/(100 g min); hypoxia: AMS-S = 47.8+/-19.5 ml/(100 g min), AMS-R = 48.2+/-10.1 ml/(100 g min), p = 0.65), and cerebral oxygen delivery remained constant. The percent change in CBF did not differ between brain regions or between groups (although absolute CBF change was greater in GM): (GM: AMS-S = 6.1+/-7.7 ml/(100 g min) (10+/-11%), AMS-R = 8.3+/-5.7 ml/(100 g min) (17+/-11%), p = 0.57; WM: AMS-S = 4.3+/-5.1 ml/(100 g min) (12+/-15%), AMS-R = 4.8+/-2.9 ml/(100 g min) (16+/-9%), p = 0.82).
  
  
  CONCLUSIONS
  CBF increases in acute hypoxia, but is not different between WM and GM, irrespective of AMS susceptibility. Acute phase differences in regional CBF during acute hypoxia are not a primary feature of susceptibility to AMS.
authors: Department of Medicine, Division of Physiology, University of California San Diego, USA.
authors: Edward A W
authors: EA
authors: Dyer
authors: Susan R
authors: SR
authors: Hopkins
authors: Joanna E
authors: JE
authors: Perthen
authors: Richard B
authors: RB
authors: Buxton
authors: David J
authors: DJ
authors: Dubowitz
mesh_terms: D000328:Adult; D000532:Altitude Sickness / Q000503:physiopathology*; D001776:Blood Circulation Time; D016022:Case-Control Studies; D002540:Cerebral Cortex / Q000098:blood supply*; D002560:Cerebrovascular Circulation / Q000502:physiology*; D005260:Female; D006339:Heart Rate; D006801:Humans; D000860:Hypoxia / Q000473:pathology* / Q000503:physiopathology*; D007091:Image Processing, Computer-Assisted; D008279:Magnetic Resonance Imaging / Q000379:methods; D008297:Male; D008875:Middle Aged; D010100:Oxygen / Q000008:administration & dosage / Q000097:blood; D012039:Regional Blood Flow / Q000502:physiology; D013997:Time Factors
chemical_list: D010100:Oxygen