Experimental and theoretical studies of oxygen gradients in rat pial microvessels

Using modified oxygen needle microelectrodes and intravital videomicroscopy, measurements were made of tissue oxygen tension (PO(2)) profiles near cortical arterioles and transmural PO(2) gradients in the pial arterioles of the rat. Under control conditions, the transmural PO(2) gradient averaged 1.17+/-0.06 mm Hg/microm (mean+/-s.e., n=40). Local arteriolar dilation resulted in a marked decrease in the transmural PO(2) gradient to 0.68+/-0.04 mm Hg/microm (P<0.001, n=38). The major finding of this study is a dependence of the transmural PO(2) gradient on the vascular tone of the pial arterioles. Using a model of oxygen transport in an arteriole and experimental PO(2) profiles, values of radial perivascular and intravascular O(2) fluxes were estimated. Our theoretical estimates show that oxygen flux values at the outer surface of the arteriolar wall are approximately 10(-5) mL O(2)/cm(2) per sec, independent of the values of the arteriolar wall O(2) consumption within a wide range of consumption values. This also means that PO(2) transmural gradients for cerebral arterioles are within the limits of 1 to 2 mm Hg/microm. The data lead to the conclusion that O(2) consumption of the arteriolar wall is within the range for the surrounding tissue and O(2) consumption of the endothelial layer appears to have no substantial impact on the transmural PO(2) gradient.