title: Cerebral oxygenation declines despite maintained orthostatic tolerance after brief exposure to gravitational stress.
abstract: 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.
authors.affiliation: Département Physiologie, Institut de Médecine Aérospatiale du Service de Santé des Armées, B.P. 73, 91223 Brétigny-sur-Orge Cédex, France. dtran@imassa.fr
authors.forename: Cong Chi Denis
authors.initials: CC
authors.lastname: Tran
authors.forename: Muriel
authors.initials: M
authors.lastname: Berthelot
authors.forename: Xavier
authors.initials: X
authors.lastname: Etienne
authors.forename: Caroline
authors.initials: C
authors.lastname: Dussault
authors.forename: Jean-Claude
authors.initials: JC
authors.lastname: Jouanin
authors.forename: Pascal
authors.initials: P
authors.lastname: Van Beers
authors.forename: André
authors.initials: A
authors.lastname: Serra
authors.forename: Charles-Yannick
authors.initials: CY
authors.lastname: Guézennec
mesh_terms: 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*
chemical_list: D006454:Hemoglobins