Abstract
The non-uniform partitioning or phase separation of red blood cells (RBCs) at a diverging bifurcation of a microvascular network is responsible for RBC heterogeneity within the network. The mechanisms controlling RBC heterogeneity are not yet fully understood and there is a need to improve the basic understanding of the phase separation phenomenon. In this context, in vitro experiments can fill the gap between existing in vivo and in silico models as they provide better controllability than in vivo experiments without mathematical idealizations or simplifications inherent to in silico models. In this study, we fabricated simple models of symmetric/asymmetric microvascular networks; we provided quantitative data on the RBC velocity, line density and flux in the daughter branches. In general our results confirmed the tendency of RBCs to enter the daughter branch with higher flow rate (Zweifach-Fung effect); in some cases even inversion of the Zweifach-Fung effect was observed. We showed for the first time a reduction of the Zweifach-Fung effect with increasing flow rate. Moreover capillary dilation was shown to cause an increase of RBC line density and RBC residence time within the dilated capillary underlining the possible role of pericytes in regulating the oxygen supply.
Highlights
Heterogeneous even in uniform networks the flow and the red blood cells (RBC) density at the inlet were maintained constant
There are two prevalent hypotheses: i) the increase is due solely to the action of arteriolar smooth muscle, locally providing higher blood flow rate[22], or ii) due to a coordinated action of both arteriolar smooth muscle and capillary pericytes[1]
We present the effects of local capillary dilation which are an in vitro confirmation of earlier findings on the possible role of pericytes that were so far only shown in silico[21]
Summary
Heterogeneous even in uniform networks (uniform vessel length and diameter) the flow and the RBC density at the inlet were maintained constant. RBC dynamics in several simple networks of micro-channels are studied in vitro These networks model cerebral microvascular networks where two major fluid dynamic factors may act simultaneously to regulate the partitioning of RBCs: i) change of hydraulic resistance (e.g. dilating/constricting the lumen of capillaries) ii) increase of the overall flow rate (by dilation of feeding arterioles). This could directly affect RBC heterogeneity and local tissue oxygenation in the brain. An asymmetric single mesh with one branch wider than the other to simulate capillary dilation (dilated model)
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