Optimal occlusion uniformly partitions red blood cells fluxes within a microvascular network

TL;DR

This study investigates how pressure feedbacks from red blood cell occlusion in narrow vessels of a zebrafish model help achieve uniform blood flow distribution across the microvascular network, revealing a trade-off with increased energy dissipation.

Contribution

It demonstrates that occlusive feedbacks are tuned to ensure uniform blood flow in microvessels, a novel insight into microvascular regulation and function.

Findings

Occlusion feedbacks are tuned to prevent short-circuiting near the heart.

Uniform flow distribution is achieved at the cost of 11-fold increased dissipation.

Pressure feedbacks help partition red blood cells evenly across microvasculature.

Abstract

In animals, gas exchange between blood and tissues occurs in narrow vessels, whose diameter is comparable to that of a red blood cell. Red blood cells must deform to squeeze through these narrow vessels, transiently blocking or occluding the vessels they pass through. Although the dynamics of vessel occlusion have been studied extensively, it remains an open question why microvessels need to be so narrow. We study occlusive dynamics within a model microvascular network: the embryonic zebrafish trunk. We show that pressure feedbacks created when red blood cells enter the finest vessels of the trunk act together to uniformly partition red blood cells through the microvasculature. Using mathematical models as well as direct observation, we show that these occlusive feedbacks are tuned throughout the trunk network to prevent the vessels closest to the heart from short-circuiting the network. Thus occlusion is linked with another open question of microvascular function: how are red blood cells delivered at the same rate to each micro-vessel? Our analysis shows that tuning of occlusive feedbacks increase the total dissipation within the network by a factor of 11, showing that uniformity of flows rather than minimization of transport costs may be prioritized by the microvascular network.