Response of human cerebral blood flow to +Gz accelerations.
Intolerance symptoms associated with high sustained +Gz (head to foot) accelerations are attributed to lack of cerebral perfusion. To determine the response of cerebral circulation to +Gz stress, cerebral blood flow (CBF) was measured in humans with the transcranial Doppler method while cephalic arterial blood pressure was calculated simultaneously using a photoplethysmographic technique. Nine volunteers performed four randomized centrifuge runs at +2 to +5 Gz with a 0.4-G/s onset rate for 30 s. Compared with the control values, for +2-, +3-, +4-, and +5-Gz profiles, CBF was reduced by 19 +/- 7, 26 +/- 8, 49 +/- 26, and 61 +/- 29% (SD), respectively, at the end of the onset and by 18 +/- 4, 21 +/- 11, 27 +/- 7, and 47 +/- 29%, respectively, in the last 20 s of the plateau of acceleration. At the end of the onset and during the plateau of +Gz acceleration, CBF was less reduced than cephalic arterial blood pressure, suggesting that some mechanisms would occur to maintain cerebral perfusion under +Gz stress. These protective mechanisms are likely due to a siphon effect and/or an autoregulatory compensation.
Ossard
G
G
Laboratoire de Médecine Aérospatiale, Centre d'Essais en Vol, Brétigny-sur-Orge, France.
Clère
J M
JM
Kerguelen
M
M
Melchior
F
F
Seylaz
J
J
D000054:Acceleration / Q000009:adverse effects*; D000328:Adult; D001794:Blood Pressure / Q000502:physiology; D002536:Cerebral Arteries / Q000502:physiology; D002560:Cerebrovascular Circulation / Q000502:physiology*; D006801:Humans; D008297:Male; D017156:Photoplethysmography; D017585:Ultrasonography, Doppler, Transcranial