Unilateral frontal decortication changes cerebral blood flow distribution during hyperbaric oxygen exposure in rats

Distribution of rCBF was measured with 10.7 ± 0.5 μm differently radiolabelled 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 after right- sided frontal decortication. A decreased tolerance to hyperbaric O₂ was found compared to normal rats of the same strain. The systolic 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 arterial acid-base balance remained normal during O₂ exposure, although a small 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 at 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 bar, 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 blood 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 undisturbed side where blood flow remained below control values. The O₂ supply to different regions varied similarly. Thus the regulation of local cerebral blood flow distribution in decorticated rats is possibly markedly different from normal rats exposed to high pressure O₂.