Hematocrit in cerebral capillaries and veins under control and ischemic conditions.

Red blood cell concentration and hematocrit were assessed in the blood flowing in the capillaries of rabbit cerebral cortex (in unstained histologic sections prepared after in situ fixation of the tissue) and in the blood samples taken from the respective veins using direct, quantitative techniques. The values appeared to be significantly higher in veins than in capillaries under control conditions. With the development of cerebral ischemia, when the blood flow in the cortex was reduced to almost half of the control level, red cell concentration and hematocrit in the blood were found to decrease markedly both in the capillaries and veins of the brain, while in the femoral veins of the same animals the values remained essentially unchanged.