Tissue oxygen tension profiles close to brain arterioles and venules in the rat cerebral cortex during the development of acute anemia.

Acute anemia (stages 1 and 2) led to decreases in pO2 at the walls of radial venules (lumen diameter 13.1 +/- 0.5 microm) and in the tissues at distances of up to 40 mum from the walls, indicating increased extraction of oxygen from the blood by the smallest microvessels. Further decreases in the blood hemoglobin concentration (stage 3) did not produce any significant changes in the nature of tissue pO2 profiles close to the walls of these microvessels. In the intercapillary space, tissue pO2 decreased in proportion to the decrease in the systemic blood hemoglobin concentration, though tissue hypoxia (p(t)O2 < or = 8-10 mmHg) was seen only in tissue in which the microvessels had inadequate (decreased) blood flow responses.