Vascular geometry and oxygen diffusion in the vicinity of artery-vein pairs in the kidney

Renal arterial-to-venous (AV) oxygen shunting limits oxygen delivery to renal tissue. To better understand how oxygen in arterial blood can bypass renal tissue, we quantified the radial geometry of AV pairs and how it differs according to arterial diameter and anatomical location. We then estimated diffusion of oxygen in the vicinity of arteries of typical geometry using a computational model. The kidneys of 6 rats were perfusion fixed and the vasculature filled with silicone rubber (Microfil(R)). A single section was chosen from each kidney and all arteries (n = 1628) identified. Intrarenal arteries were largely divisible into two types , characterized by the presence or absence of a close physical relationship with a paired vein. Arteries with a close physical relationship with a paired vein were more likely to have a larger rather than smaller diameter, and more likely to be in the inner-cortex than the mid- or outer-cortex. Computational simulations indicated that direct diffusion of oxygen from an artery to a paired vein can only occur when the two vessels have a close physical relationship. However, even in the absence of this close relationship oxygen can diffuse from an artery to periarteriolar capillaries and venules. Thus, AV oxygen shunting in the proximal pre-glomerular circulation is dominated by direct diffusion of oxygen to a paired vein. In the distal pre-glomerular circulation, it may be sustained by diffusion of oxygen from arteries to capillaries and venules close to the artery wall, which is subsequently transported to renal veins by convection.