Journal of Applied Physiology, Vol 78, Issue 6 2109-2114, Copyright © 1995 by American Physiological Society
Repeated exposure to 5 bar normoxic He-N2 changes cerebral blood flow distribution in rats
G. W. Bergo and I. Tyssebotn
Department of Physiology, University of Bergen, Norway.
The regional cerebral blood flow (rCBF), arterial pressure (AP), heart
rate, respiratory frequency, and arterial acid-base chemistry were measured
during control periods at 1 bar air and after 15 and 60 min at 5 bar
normoxic He (4.0 bar)-N2 (0.8 bar) in two groups of awake habituated rats.
Group 1 (10 control rats) were exposed 40 times while restrained for 1 h in
the pressure chamber at 1 bar air. Group 2 (10 rats) were restrained and
exposed 40 times to normoxic 5 bar He-N2 atmosphere in the pressure chamber
for 45 min. During the control period, the systolic and mean AP levels were
higher (P < 0.05), whereas the average CBF and nine rCBF values were
lower in the preexposed group. During 5-bar exposure, the systolic AP rose
significantly in both groups, whereas the mean AP remained at the control
level or was reduced. The arterial O2, CO2, and HCO3 changed identically in
both groups relative to hyperventilation. Generally, the total and local
CBF values increased during the first 15 min in both groups and for 60 min
in the preexposed rats. After 60 min of exposure, the flow returned toward
the control level in most regions in both groups, whereas the flow was
still elevated in the cerebellum and mesencephalon in the control rats and
in the bulbus olfactorius, mesencephalon, medulla oblongata, spinal cord,
and posterior part of cortex cerebri in preexposed animals. Hypothalamic
rCBF in control rats was reduced after 60 min.(ABSTRACT TRUNCATED AT 250
WORDS)
