Blood flow through vasa vasorum in arteries and veins: effects of luminal PO2.

We have examined effects of chronic reduction of intraluminal PO2 on blood flow through vasa vasorum, by comparing large arteries and veins, and effects of acute hypoxia on flow through vasa. Microspheres were used to measure flow in anesthetized dogs. Values obtained with different sizes of microspheres suggest that spheres 9 and 15 micron in diam, but not 50 micron, are appropriate for measurement of blood flow through vasa vasorum. Flow [expressed as ml X min-1 X 100 g-1 (SE)] through medial vasa was similar in the aorta (9.0 +/- 2.1) and pulmonary artery (9.3 +/- 1.1) although, on the basis of wall thickness and number of lamellae, one would predict much higher levels of flow to aortic media. Two veins that we studied have a thick muscular wall. Both veins had high levels of flow through medial vasa: 33 +/- 4.4 to the subdiaphragmatic inferior vena cava and 18 +/- 5.4 to the portal vein. Two other veins are apparently conduit vessels, with dense connective tissue and minimal smooth muscle. Both veins had minimal flow through medial vasa: 2.4 +/- 1.0 to superior vena cava, and 1.9 +/- 0.8 to supradiaphragmatic inferior vena cava. Thus, because flow through vasa differs greatly in different veins, structure of the vessel (as well as intraluminal PO2) is an important determinant of flow through vasa. Acute hypoxia increased conductance of medial vasa vasorum of arteries and veins when neurohumoral constrictor effects were blocked by phenoxybenzamine.(ABSTRACT TRUNCATED AT 250 WORDS)