Journal of Applied Physiology, Vol 76, Issue 6 2527-2534, Copyright © 1994 by American Physiological Society
Cortical blood flow and +Gz acceleration in conscious rabbits
G. Florence, P. Roucher, R. Vallet, M. Lemenn, R. Charbonne and J. Seylaz
Centre d'Etudes et de Recherches de Medecine Aerospatiale, Section de Physiologie Comparee, Bretigny sur Orge, France.
We examined whether superficial cortical blood flow (CBF) of
nonanesthetized rabbits (n = 11) is affected by gravitational (G) stress.
Blood flow was measured by laser-Doppler flowmetry through a chronic
Plexiglas window implanted over the parietal cortex. Mean arterial blood
pressure (MABP) was recorded via an aortic catheter with the pressure
transducer situated at the level of the head. The electrocorticogram (ECoG)
was also studied in seven rabbits. The animals were exposed to tail-to-head
acceleration [6, 10, 15, and 20 G acceleration (Gz) for 1 min]. MABP fell
with increasing acceleration (regression line equation: MABP = -7.0 Gz +
129.1; P < 0.001, r = 0.85), whereas CBF was statistically either not
different from or greater than control. In one rabbit exposed to 20 Gz,
high voltage and slow waves were observed on the ECoG and these changes
were preceded by a decrease in CBF to 66% of control. We conclude that the
stress and the siphon effect may account for the maintenance of elevated
CBF despite low or negative MABP until the occurrence of vascular collapse
that induces loss of consciousness.
