UNILATERAL FRONTAL DECORTICATION CHANGES CEREBRAL BLOOD-FLOW DISTRIBUTION DURING HYPERBARIC-OXYGEN EXPOSURE IN RATS

Distribution of rCBF was measured with 10.7 +/- 0.5 mum differently ra diolabelled microspheres (MS) during control at 1 bar air, and after 5 and 35 min at 5 bar (0.5 MPa) 95% O2 on awake, habituated rats 10 d a fter right-sided frontal decortication. A decreased tolerance to hyper baric O2 was found compared to normal rats of the same strain. The sys tolic arterial pressure increased during O2 exposure (11%, p < 0.05), the mean arterial pressure remained unchanged, but the cardiac output and heart rate fell by 29 and 14% (p < 0.01), respectively. The arteri al acid-base balance remained normal during O2 exposure, although a sm all reduction of CO2 (24%) and HCO3 (11%) WaS observed (p < 0.01 and p < 0.05), possibly due to increased alveolar ventilation caused by an elevated respiratory rate of 24% (p < 0.05). The arterial O2 content a t 5 bar increased by about 30% (p < 0.01). During control, blood flow in 16 regions of each hemisphere was found to be lower, more scattered , and differently distributed on the lesioned side. After 5 min at 5 b ar, the blood flow fell in nearly all regions of the brain (up to 40%) , similarly in the two brain halves. During the 35 min exposure, the b lood flow increased, so that 60% of the examined areas on the lesioned side had blood flow levels of control or above, in contrast to the un disturbed side where blood flow remained below control values. The O2 supply to different regions varied similarly. Thus the regulation of l ocal cerebral blood flow distribution in decorticated rats is possibly markedly different from normol rats exposed to high pressure O2.