A quantitative analysis of the factors influencing oxygen diffusion in the vicinity of artery-vein pairs in the kidney

Abstract

Background: Diffusion of oxygen from arteries to veins in the kidney (AV oxygen shunting) acts to limit oxygen delivery to renal tissue. We recently employed computational modeling to identify two factors critical to determination of the quantity of AV oxygen shunting within the renal circulation. These were (i) the distance between the artery and the vein, and (ii) the degree to which the vein wraps around the wall of the artery. Aim: To quantify how the factors in (i) and (ii) above change along the course of the renal circulation. Methods: The renal vasculature of Sprague Dawley rats (n=6) was perfusion fixed and filled with Microfil®. A section from each kidney was chosen and the shortest arterial/arteriolar diameter, distance to the nearest vein, and the degree to which a vein wraps an artery were measured. Results: The diffusion distance between arteries and veins increased with decreasing arte-rial diameter (Figure 1). The proportion of the arterial wall surrounded by the vein (wrapping) decreased as arterial diameter decreased (Figure 2). Conclusions: The spatial relationships (separation and wrapping) between arteries and veins that promote AV oxygen shunting are more prominent in the larger vessels than the smaller vessels of the kidney. These observations challenge the conventional notion that most AV oxygen shunting occurs in the smaller cortical vessels (e.g., interlobular arteries) after the divergence of the cortical and medullary circulations. Thus, AV oxygen shunting may limit oxygen delivery to the renal medulla as well as the renal cortex