Journal of Applied Physiology, Vol 57, Issue 6 1803-1808, Copyright © 1984 by American Physiological Society
Nonuniform brain blood flow response to hypoxia in unanesthetized cats
J. A. Neubauer and N. H. Edelman
In seven unanesthetized cats, radiolabeled microspheres were used to
determine regional brain blood flow (rBBF) to the medulla-pons (M-P),
midbrain-thalamus (M-T), cerebellum (Cb), and cortex (Cx) during three
conditions: 1) control [arterial O2 tension (PaO2) = 81 Torr, arterial CO2
tension (PaCO2) = 26 Torr]; 2) hypocapnic hypoxia (PaO2 = 39 Torr, PaCO2 =
22 Torr); and 3) isocapnic hypoxia (PaO2 = 47 Torr, PaCO2 = 26 Torr).
Hypoxia increased blood flow significantly more in the caudal brain stem
(M-P) than in the Cx (P less than 0.05) during both hypocapnic hypoxia
(M-P/Cx: +33/ +17 ml X min-1 X 100 g-1) and isocapnic hypoxia (M-P/Cx: +13/
-2 ml X min-1 X 100 g-1). Since sympathetic innervation is greater
anatomically to rostral than to caudal vessels, we examined the rBBF
response to hypocapnic hypoxia in seven additional cats after unilateral
superior cervical gangliectomy. All seven cats had a reduction in the
cortical-to-caudal brain stem trend on the denervated side of the brain
(M-P/Cx: +27/+28 ml X min-1 X 100 g-1) compared with the intact side of the
brain (M-P/Cx: +34/+24 ml X min-1 X 100 g-1) owing to both increases in Cx
and decreases in M-P flows. We conclude that in unanesthetized cats hypoxia
causes a greater increase in the caudal brain stem compared with cortical
blood flow, and this differential response is related to modulation by the
sympathetic nervous system.(ABSTRACT TRUNCATED AT 250 WORDS)
