Cerebral ischemia and reperfusion increases the heterogeneity of local oxygen supply/consumption balance

Background and Purpose - After cerebral vessel blockage, local blood flow and O₂ consumption becomes lower and oxygen extraction increases. With reperfusion, blood flow is partially restored. We examined the effects of ischemia-reperfusion on the heterogeneity of local venous oxygen saturation in rats in order to determine the pattern of microregional O₂ supply/consumption balance in reperfusion. Methods - The middle cerebral artery was blocked for 1 hour using the internal carotid approach in 1 group (n=9) and was then reperfused for 2 hours in another group (n=9) of isoflurane- anesthetized rats. Regional cerebral blood flow was determined using a C ¹⁴-iodoantipyrine autoradiographic technique. Regional small vessel arterial and venous oxygen saturations were determined microspectrophotometrically. Results - After 1 hour of ischemia, local cerebral blood flow (92±10 versus 50±10 mL/min per 100 g) and O₂ consumption (4.5±0.6 versus 2.7±0.5 mL O₂/min per 100 g) decreased compared with the contralateral cortex. Oxygen extraction increased (4.7±0.2 versus 5.4±0.3 mL O₂/100 mL) and the variation in small vein (20-60 μm) O₂ saturation as determined by its coefficient of variation (=100×SD/mean) increased (5.5 versus 10.5). With 2 hours of reperfusion, the blood flow decrement was reduced and O ₂ consumption returned to the value in the contralateral cortex. Oxygen extraction remained elevated in the ischemic-reperfused area and the coefficient of variation of small vein O₂ saturation increased further (17.3). Conclusions - These data indicated continued reduction of O ₂ supply/consumption balance with reperfusion. They also demonstrated many small regions of low oxygenation within the reperfused cortical region.