Effects of high altitude exposure on cerebral hemodynamics in normal subjects.
OBJECTIVE
Acute mountain sickness (AMS) may be an early stage of high altitude cerebral edema. If so, AMS could result from an alteration of dynamic autoregulation of cerebral blood flow resulting in overperfusion of capillaries and vasogenic cerebral edema.


METHODS
We measured middle cerebral artery blood flow velocity (Vmca) by transcranial Doppler and arterial blood pressure by finger plethysmography at 490 m and 20 hours after arrival at 4559 m in 35 volunteers who had been randomized to tadalafil, dexamethasone, or placebo in a study on the pharmacological prevention of high altitude pulmonary edema. A dynamic cerebral autoregulation index (ARI) was calculated from continuous recordings of Vmca and blood pressure during transiently induced hypotension.


RESULTS
Altitude was associated with an increase in a cerebral-sensible AMS (AMS-C) score (P<0.001) and with a decrease in arterial oxygen saturation (Sao2), whereas average Vmca or ARI did not change. However, at altitude, the subjects with the lowest ARI combined with the lowest Sao2 presented with the highest AMS-C score (P<0.03). In addition, a stepwise multiple linear regression analysis on arterial Pco2, Sao2, and baseline or altitude ARI identified altitude ARI as the only significant predictor of the AMS-C score (P=0.01). The AMS-C score was lower in dexamethasone-treated subjects compared with high altitude pulmonary edema-susceptible untreated subjects. Neither tadalafil nor dexamethasone had any significant effect on Vmca or ARI.


CONCLUSIONS
High altitude hypoxia is associated with impairment in the regulation of the cerebral circulation that might play a role in AMS pathogenesis.
Van Osta
Aurélie
A
Laboratory of Physiology, Faculty of Medicine, Free University of Brussels, Belgium.
Moraine
Jean-Jacques
JJ
Mélot
Christian
C
Mairbäurl
Heimo
H
Maggiorini
Marco
M
Naeije
Robert
R
D000328:Adult; D000531:Altitude; D000532:Altitude Sickness / Q000517:prevention & control; D001783:Blood Flow Velocity / Q000502:physiology; D002243:Carbolines / Q000627:therapeutic use; D002536:Cerebral Arteries / Q000502:physiology; D002540:Cerebral Cortex / Q000098:blood supply*; D003907:Dexamethasone / Q000627:therapeutic use; D004338:Drug Combinations; D005260:Female; D006439:Hemodynamics / Q000502:physiology*; D006706:Homeostasis / Q000502:physiology; D006801:Humans; D008297:Male; D008875:Middle Aged; D009051:Mountaineering / Q000502:physiology; D011654:Pulmonary Edema / Q000517:prevention & control; D000068581:Tadalafil; D017585:Ultrasonography, Doppler, Transcranial / Q000379:methods
D002243:Carbolines; D004338:Drug Combinations; D000068581:Tadalafil; D003907:Dexamethasone