The impact of capillary dilation on the distribution of red blood cells in artificial networks

Abstract

Recent studies suggest that pericytes around capillaries are contractile and able to alter the diameter of capillaries. To investigate the effects of capillary dilation on network dynamics, we performed simulations in artificial capillary networks of different sizes and complexities. The unequal partition of hematocrit at diverging bifurcations was modeled by assuming that each red blood cell (RBC) enters the branch with the faster instantaneous flow. Network simulations with and without RBCs were performed to investigate the effect of local dilations. The results showed that the increase in flow rate due to capillary dilation was less when the effects of RBCs are included. For bifurcations with sufficient RBCs in the parent vessel and nearly equal flows in the branches, the flow rate in the dilated branch did not increase. Instead, a self-regulation of flow was observed due to accumulation of RBCs in the dilated capillary. A parametric study was performed to examine the dependence on initial capillary diameter, dilation factor, and tube hematocrit. Furthermore, the conditions needed for an efficient self-regulation mechanism are discussed. The results support the hypothesis that RBCs play a significant role for the fluid dynamics in capillary networks and that it is crucial to consider the blood flow rate and the distribution of RBCs to understand the supply of oxygen in the vasculature. Furthermore, our results suggest that capillary dilation/constriction offers the potential of being an efficient mechanism to alter the distribution of RBCs locally and hence could be important for the local regulation of oxygen delivery.

Red blood cell phase separation in symmetric and asymmetric microchannel networks: effect of capillary dilation and inflow velocity

“…Second, 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. Finally, we present results for the stretched model which demonstrate that the Zweifach-Fung effect depends on the inflow rate.…”

“…There are conflicting opinions on whether RBCs prefer to enter the daughter vessel with higher flow rate62744 or with higher bulk velocity1221. In the present study, we circumvent this problem by working with models with equal cross-sections in the daughter branches just after the bifurcation.…”

“…Computational simulations818 of blood rheology in microcirculatory networks of the rat mesentery have shown that blood flow can undergo spontaneous, self-sustained oscillations in capillaries under steady conditions without any active biological regulation. Recent studies with droplets131920 and RBCs1221 suggested that the topology of the network can lead to dynamic changes of the hematocrit ( Ht ) within the network. Computational models of idealized networks12 showed that RBC distribution and velocities are irregular and heterogeneous even in uniform networks (uniform vessel length and diameter) although the flow and the 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 rate22, or ii) due to a coordinated action of both arteriolar smooth muscle and capillary pericytes (contractile cells which are able to alter the lumen of capillaries)1. Recent computational results21 showed that capillary dilation/constriction (e.g. due to pericytes) could be a good local regulator of oxygen delivery by varying locally the distribution of RBCs.…”

Going beyond 20 μm-sized channels for studying red blood cell phase separation in microfluidic bifurcations

“…12,13,[21][22][23]27,36,38,41,42 In these works, the complex rheological properties of blood flow in microcirculation, especially the phase separation effect, are either described by empirical laws obtained by least-square adjustment to experimental results (e.g., Refs. 21 and 36), theoretically derived assuming a given RBC flow regime (e.g., single file RBC flows in narrow capillaries 27 ), or modeled in an ad hoc fashion.…”