Abstract
Although bulk changes in red blood cell concentration between vessels have been well characterised, local distributions are generally overlooked. Red blood cells aggregate, deform and migrate within vessels, forming heterogeneous distributions which have considerable effect on local haemodynamics. The present study reports data on the local distribution of human red blood cells in a sequentially bifurcating microchannel, representing the branching geometry of the microvasculature. Imaging methodologies with simple extrapolations are used to infer three dimensional, time-averaged velocity and haematocrit distributions under a range of flow conditions. Strong correlation between the bluntness of the velocity and haematocrit profiles in the parent branch of the geometry is observed and red blood cell aggregation has a notable effect on the observed trends. The two branches of the first bifurcation show similar characteristics in terms of the shapes of the profiles and the extent of plasma skimming, despite the difference in geometric configuration. In the second bifurcation, considerable asymmetry between the branches in the plasma skimming relationship is observed, and elucidated by considering individual haematocrit profiles. The results of the study highlight the importance of considering local haematocrit distributions in the analysis of blood flow and could lead to more accurate computational models of blood flow in microvascular networks. The experimental approaches developed in this work provide a foundation for further examining the characteristics of microhaemodynamics.
Highlights
Understanding and predicting blood characteristics is an important part of both clinical care and research into fundamental understanding of physiology and pathology
The present study provides high resolution quantitative data on red blood cells (RBCs) concentrations, yielding further insight into the interactions between local haematocrit distributions, the geometry and the flow conditions
In a previous study in high aspect ratio (100640 mm) straight Tbifurcations [12], we found negligible plasma skimming for phosphate buffered saline (PBS) data (B~1:04), but moderate plasma skimming for the Dextran data (B~1:14); a level comparable to the present data
Summary
Understanding and predicting blood characteristics is an important part of both clinical care and research into fundamental understanding of physiology and pathology. The deformability of RBCs results in several phenomena which significantly affect haemodynamics Due to their deformability, RBCs migrate away from vessel walls, resulting in a region of reduced RBC concentration (haematocrit) close to the walls. RBCs migrate away from vessel walls, resulting in a region of reduced RBC concentration (haematocrit) close to the walls This leads to the Fahraeus effect; a reduction in bulk haematocrit as vessel size decreases. Using high-speed photography, it is possible to measure the distance between the vessel wall and the first RBC optically, and to describe the CDL distribution in straight vessel sections. The distribution of RBCs in a vessel or channel varies continuously in the radial direction and has been measured by a number of researchers in vitro in straight geometries [6,8,9]. We quantified the haematocrit distribution in a simple T-bifurcation and showed that in the daughter branch the haematocrit distribution was asymmetric, and the velocity profiles correspondingly skewed in the opposite direction, due to the influence of local haematocrit on viscosity [12]
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