[Changes in RCBF and edema after transient cerebral ischemia--ischemic threshold of postischemic hypoperfusion]

Brain damage after transient cerebral ischemia may be related to changes in postischemic cerebral blood flow and brain edema. In this study, the relationship between postischemic cerebral blood flow and edema was evaluated in the gerbil. Bilateral carotid occlusion (for 1, 1.5, 5, 15, or 30 min) was carried out in 110 female gerbils (50-70 g) under anesthesia with 2% halothane in 30% O2 and 70% NO2. Cerebral blood flow was measured by a [14C]-iodoantipyrine method modified slightly for use in small animals, and brain edema was evaluated by a specific gravity method. The threshold duration of ischemia which gives rise to subsequent hypoperfusion or edema was also established. In another 52 female gerbils under the same anesthesia, we investigated the effect of ischemia of variable duration on postischemic blood pressure and blood gas. Throughout all experiments, rectal temperature was maintained at 37-38 degrees C with a heating pad. Student's t test was used to calculate statistical significance. Neither blood pressure nor blood gas did vary significantly at any time following recirculation. Each brain region showed the same pattern of blood flow change, one almost independent of duration of occlusion. Namely, after the release of occlusion, transient recovery of blood flow was observed. But the flow then fell to 30-40% of the normal value at 1 h, after which it returned up to normal at 6 h. The severity of postischemic hypoperfusion was also independent of occlusion time. Interestingly, we did not observe postischemic hyperemia in any experimental groups except mild hyperemia in hippocampus after 5 and 15 min ischemia.(ABSTRACT TRUNCATED AT 250 WORDS)