Cerebral oxygenation declines despite maintained orthostatic tolerance after brief exposure to gravitational stress.
We examined the effect of a single 120 s of exposure to +3Gz (head-to-foot inertial forces) centrifugation as orthostatic stress on cerebral oxygenation (oxy-Hb) and cerebral blood volume (CBV) changes in response to stand test, in order to relate the occurrence of altered cerebral oxygenation control to any increase in sympathetic activity. Frontal near-infrared spectroscopy and mean arterial blood pressure at brain level (MAPbrain) were recorded in 14 subjects in supine and then in standing (10 min) position, before and after +3Gz centrifugation. The decrease in oxy-Hb (-7 +/- 5 a.u. versus -27 +/- 4 a.u., P<0.001) and in CBV (-6 +/- 10 a.u. versus -15 +/- 8 a.u., P<0.05) upon standing was more important after +3Gz centrifugation, with unchanged MAPbrain (-8 +/- 8 mmHg versus -3 +/- 11 mmHg). Upon standing, the high-frequency component of heart rate was lower (1090 +/- 460 ms2 versus 827 +/- 412 ms2, P<0.05) after +3Gz centrifugation. These findings suggest a downward shift in the static cerebral autoregulatory curve. We conclude that cerebral vasoconstriction might have occurred without centrally mediated increase in the entire peripheral sympathetic activity of the body.
Tran
Cong Chi Denis
CC
Département Physiologie, Institut de Médecine Aérospatiale du Service de Santé des Armées, B.P. 73, 91223 Brétigny-sur-Orge Cédex, France. dtran@imassa.fr
Berthelot
Muriel
M
Etienne
Xavier
X
Dussault
Caroline
C
Jouanin
Jean-Claude
JC
Van Beers
Pascal
P
Serra
André
A
Guézennec
Charles-Yannick
CY
D000328:Adult; D001783:Blood Flow Velocity; D001794:Blood Pressure / Q000502:physiology; D001921:Brain / Q000098:blood supply*; D002560:Cerebrovascular Circulation / Q000502:physiology*; D004562:Electrocardiography; D004569:Electroencephalography; D004576:Electromyography; D007839:Functional Laterality / Q000502:physiology; D006112:Gravitation; D006339:Heart Rate / Q000502:physiology; D006454:Hemoglobins / Q000378:metabolism; D006801:Humans; D007024:Hypotension, Orthostatic / Q000503:physiopathology*; D008297:Male; D008875:Middle Aged; D019265:Spectroscopy, Near-Infrared / Q000379:methods; D013312:Stress, Physiological / Q000503:physiopathology*
D006454:Hemoglobins