Blood volume and flow velocity through parenchymal microvessels in ischemic brain edema of rats

Focal cerebral ischemia was produced in rats with left middle cerebral artery occlusion for 24 hours. Regional CBF was measured by the 14C-iodoantipyrine technique. The distribution of red blood cells (RBC) and plasma in cerebral microvessels was determined by radioluminography using 51Cr-RBC and 125I-bovine serum albumin, respectively. The mean transit times of RBC and plasma, blood volume, and hematocrit were calculated. The water content was measured by specific gravity. The blood flow was reduced to 2% of the control value in the central core, where the brain edema was the most severe. The blood volume decreased to 25% and the mean transit times of RBC and plasma increased about tenfold. In the outer periphery, where CBF was reduced to 39% but brain edema was not induced, the blood volume was decreased to 76% while the mean transit time of RBC was increased 2.1-fold, being greater than the increase in the plasma transit time. These findings indicate that focal ischemia has variable effects on the blood volume and flow velocities of RBC and plasma in the parenchymal microvessels depending on the depth of blood flow and edema. A decrease in blood flow is probably related to a reduction in the flow velocities of RBC and plasma in the surrounding ischemic tissue rather than to decreased number of perfused capillaries in the ischemic core.