Functional optimization of the arterial network

TL;DR

This paper models the evolution of mammalian arterial networks by optimizing blood flow and hematocrit under physiological constraints, revealing how pressure regulation and vessel scaling support efficient oxygen delivery.

Contribution

It introduces a novel optimization model incorporating blood rheology and vessel scaling laws to explain arterial network evolution and physiological parameter selection.

Findings

Optimal hematocrit of 0.43 aligns with physiological data.

Vessel diameter decrease ratio of about 0.79 matches observed anatomy.

Pressure drops are crucial for maintaining oxygen supply efficiency.

Abstract

We build an evolutionary scenario that explains how some crucial physiological constraints in the arterial network of mammals - i.e. hematocrit, vessels diameters and arterial pressure drops - could have been selected by evolution. We propose that the arterial network evolved while being constrained by its function as an organ. To support this hypothesis, we focus our study on one of the main function of blood network: oxygen supply to the organs. We consider an idealized organ with a given oxygen need and we optimize blood network geometry and hematocrit with the constraint that it must fulfill the organ oxygen need. Our model accounts for the non-Newtonian behavior of blood, its maintenance cost and F\aa hr\ae us effects (decrease in average concentration of red blood cells as the vessel diameters decrease). We show that the mean shear rates (relative velocities of fluid layers) in the tree vessels follow a scaling law related to the multi-scale property of the tree network, and we show that this scaling law drives the behavior of the optimal hematocrit in the tree. We apply our scenario to physiological data and reach results fully compatible with the physiology: we found an optimal hematocrit of 0.43 and an optimal ratio for diameter decrease of about 0.79. Moreover our results show that pressure drops in the arterial network should be regulated in order for oxygen supply to remain optimal, suggesting that the amplitude of the arterial pressure drop may have co-evolved with oxygen needs.