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

Abstract

 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°A (first-order branch) arterioles to 61.5±12 mmHg on 5°A arterioles. Transmural flux of oxygen from blood to tissue increased markedly at the level of minute 4°A–5°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 SO_2; 82±9%) and 258±19 µm 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/µm (SO₂ 0.1±0.06%/µm). 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.