Journal of Applied Physiology
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J Appl Physiol 76: 2114-2118, 1994;
8750-7587/94 $5.00
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Journal of Applied Physiology, Vol 76, Issue 5 2114-2118, Copyright © 1994 by American Physiological Society

ARTICLES

Response of human cerebral blood flow to +Gz accelerations

G. Ossard, J. M. Clere, M. Kerguelen, F. Melchior and J. Seylaz
Laboratoire de Medecine Aerospatiale, Centre d'Essais en Vol, Bretigny-sur-Orge, France.

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.


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