Reperfusion of focal ischemia of varying duration: postischemic hyper- and hypo-perfusion.

Reperfusion into focal ischemia was studied in 25 cats after middle cerebral artery (mca) occlusion of 15 min to 2 hours duration. Changes in cerebral blood flow (CBF) were followed with the hydrogen clearance method in the center and periphery of the ischemic lesion expected. Postischemic hyperperfusion was found often after 15 and 30 min ischemia and regularly after 60 min mca occlusion. It was followed by normal flow after 15 and 30 min occlusion and by postischemic hypoperfusion after 1 hour ischemia. After 2 hours occlusion hypoperfusion generally was not preceded by hyperperfusion. After 60 min ischemia hyperperfusion could not prevent the development of severe hypoperfusion, but often was accompanied by a marked flow reduction in the periphery of the mca territory. The data indicate that hyperperfusion after ischemic periods lasting 60 min and more induces hypoperfusion in the area itself and in neighbouring regions by affecting perfusion pressure and thereby may enlarge ischemic damage.