Distribution of oxygen tension on the surface of arterioles, capillaries and venules of brain cortex and in tissue in normoxia: an experimental study on rats.

The distribution of oxygen tension (PO2) was studied in normoxia on the surface of arterioles, capillaries and venules of rat brain cortex, both longitudinally and in tissue radially from the wall of microvessels. Along the arteriolar tree, PO2 decreased from 81.2+/-6. 2 mmHg (mean+/-SD) on 1 degrees A (first-order branch) arterioles to 61.5+/-12 mmHg on 5 degrees A arterioles. Transmural flux of oxygen from blood to tissue increased markedly at the level of minute 4 degrees A-5 degrees A arterioles. At the arterial end of cortical capillaries, PO2 averaged 57.9+/-10.6 mmHg, n=19, (or, in terms of blood oxygen saturation SO2; 82+/-9%) and 258+/-19 microm downstream 40.9+/-11.5 mmHg, n=19, (SO2 59+/-18%). The averaged PO2 drop on the capillaries studied was 17+/-9 mmHg, and the longitudinal PO2 gradient was accordingly 0.07+/-0.04 mmHg/ microm (SO2 0.1+/-0.06%/ microm). The radial profiles of tissue PO2 recorded near arterioles, capillaries and venules clearly demonstrated that all these microvessels supply oxygen to brain tissue. The PO2 distribution on venules was characterized by pronounced heterogeneity.