Partitioning of red blood cell aggregates in bifurcating microscale flows

Abstract

Microvascular flows are often considered to be free of red blood cell aggregates, however, recent studies have demonstrated that aggregates are present throughout the microvasculature, affecting cell distribution and blood perfusion. This work reports on the spatial distribution of red blood cell aggregates in a T-shaped bifurcation on the scale of a large microvessel. Non-aggregating and aggregating human red blood cell suspensions were studied for a range of flow splits in the daughter branches of the bifurcation. Aggregate sizes were determined using image processing. The mean aggregate size was marginally increased in the daughter branches for a range of flow rates, mainly due to the lower shear conditions and the close cell and aggregate proximity therein. A counterintuitive decrease in the mean aggregate size was apparent in the lower flow rate branches. This was attributed to the existence of regions depleted by aggregates of certain sizes in the parent branch, and to the change in the exact flow split location in the T-junction with flow ratio. The findings of the present investigation may have significant implications for microvascular flows and may help explain why the effects of physiological RBC aggregation are not deleterious in terms of in vivo vascular resistance.

Red blood cell aggregate flux in a bifurcating microchannel

“…F* = F Daughter / F Parent ) was introduced for each aggregate size A*examined in the study (1 to 7) and plotted against the normalized flow ratio Q*. Figure 4a shows the edge area distribution in the parent branch for a flow ratio Q* of ~ 0.1 as reported in Kaliviotis et al [15]. The RBC aggregation phenomenon causes distinct changes in the microstructure of the fluid and this is reflected in the statistics of the data in Figure 4a (the distribution is left-truncated at 0.5 for the purpose of noise reduction).…”

“…These patterns can be identified with edge detection algorithms. It was shown that these iso-intensity areas increase almost linearly with the number of RBCs per aggregate for small aggregates of up to 15 RBCs per aggregate [14,15]. The detection algorithm is briefly described below.…”

“…In the aforementioned study it was also shown that large RBC aggregates show a preference towards the central locations of the channel and this was explained in view of the lower shear forces developed in the regions, compared to those developed close to the boundaries of the flow configuration. The same methodology was recently applied to RBC flows in a T-type bifurcating microchannel [15] in order to examine the aggregate size characteristics. The experiments were performed with aggregating and nonaggregating samples and the effect of the daughter branch flow rate ratio (i.e.…”

“…In this paper, we report on a study of RBC aggregate size fluxes in a T-junction for the first time, estimated through analysis of the bifurcating flows reported in Sherwood et al [11,12], using the aggregate detection methodology developed by Kaliviotis et al [14,15]. The paper is structured as follows: in the Methodology section the technique for flux calculation is described and information regarding sample preparation, the flow system, and flux calculation is provided; in the Results and discussion section the presentation and analysis of the RBC aggregate size flux is presented for 34 different flow splits (i.e.…”

“…Our previous work on red blood cell transport in straight and bifurcating microchannels (Sherwood et al [11][12][13] and Kaliviotis et al [14,15]) has investigated the cell depleted layer (CDL) formed near the walls, the spatial variation of RBC concentrations, the phenomenon of plasma skimming and the aggregate size distribution. A comprehensive literature review on these characteristics for in vivo and in vitro studies was also provided therein.…”