The role of red blood cell occlusion in zebrafish trunk vascular network

Capillary networks are responsible for gas exchange in the tissues, where red blood cells release their oxygen and receive carbon dioxide. Red blood cell deforms when it travels through fine vessels, leading to membrane deformation and transient large pressure difference across the vessel. Microfluidic experiments show in vitro that this occlusion could cause the stagnation and the rupture of cell, which clearly hinders the function of red blood cell of delivering oxygen. On the other hand this occlusion can be easily circumvented by a slight increase in vessel radius as suggested by lubrication calculation. It is not clear what is the biological role of this deliberately maintained red blood cell occlusion. In this work I show that in zebrafish embryo this occlusion is essential for tuning the flow in the finest vessels. Without this occlusion the flow exhibits an exponential decay from head to tail, which does not agree with the experimental data. When the tuned occlusion is incorporated in a droplet traffic model the uniform flow is achieved, but under a trade-off with the transport efficiency. We explored the flow uniformity and transport efficiency in a larger physiological parameter space, and showed that the occlusion is carefully tuned to strike a balance between these two important network properties (paper [4] in publication).

(A) The zebrafish trunk vasculature achieves a narrow 1D manifold of maximal flow uniformity. (B) A trade-off between flow uniformity (heat map) and transport efficiency (white level curves) is exhibited.