Effect of uneven red cell influx on formation of cell-free layer in small venules

• There was an asymmetric formation of CFL downstream of a venular bifurcation.
• Such an asymmetric CFL formation was due to uneven influx of RBCs.
• Flow resistance could significantly be increased by the asymmetric CFL formation.
• This CFL effect might become more pronounced in pathological flow conditions.

This study examined how the uneven influx of red blood cells (RBCs) from feeding vessels influences formation of cell-free layer (CFL) in the downstream vessel of a venular bifurcation. Spatio-temporal variations of the CFL width along the downstream vessel (19–41-μm inner diameter, D) were determined at 0.5D intervals from 0.5D to 3.0D away from the bifurcation. Upstream flow conditions were quantified by the ratio of volume flow rates (Q⁎ = QHigh / QLow) between high flow (QHigh) and low flow feeding (QLow) vessels. The RBC aggregation level in the rats was adjusted to be at healthy human levels by infusing Dextran 500. Our results suggested that the CFL formation process could be seen only from 2.0D away from the bifurcating point. The mean CFL width at the wall adjacent to the feeding vessel with a higher flow rate was consistently greater than that at the opposite wall, leading to an asymmetric CFL formation in the vessel. A positive relation (P < 0.05) between the asymmetry of the CFL width and the volume flow rate ratio (Q⁎) was found. Our numerical prediction showed that flow resistance in the venular network could be significantly increased by the asymmetric formation of CFL downstream and this effect might become more pronounced under pathological flow conditions such as hyper-aggregating and/or low shear conditions.