Control of low flow regions in the cerebral vasculature sets an optimal arteriole-venule number ratio.

Lacking any ability to store glucose, the mammalian brain relies on a constant glucose and oxygen supply via the cerebral vasculature. In the cortex, this supply is maintained by parallel arterioles and venules. Yet, analysis of both real cortical microvasculature modeled as networks and idealized vasculature modeled by a slender-body theory approach shows that far from being perfused uniformly, the cortex is strewn with regions of very low flow. Increasing the number of perfusing vessels increases the number of low-flow spots. Minimizing the influence of low flow spots sets an optimal arteriole-venule ratio that we find to be closely recapitulated in data from real mammalian cortices. Further, low flow regions complicate the regulation of metabolite delivery with neuronal activity, leading to unintuitive changes in perfusion when penetrating vessels dilate.