Synergy between shear-induced migration and secondary flows on red blood cells transport in arteries: considerations on oxygen transport

Shear-induced migration of red blood cells (RBCs) is a well-known\udphenomenon characterizing blood flow in the small vessels (micrometre to\udmillimetre size) of the cardiovascular system. In large vessels, like the\udabdominal aorta and the carotid artery (millimetre to centimetre size), the\udextent of this migration and its interaction with secondary flows has not\udbeen fully elucidated. RBC migration exerts its influence primarily on platelet\udconcentration, oxygen transport and oxygen availability at the luminal\udsurface, which could influence vessel wall disease processes in and adjacent\udto the intima. Phillips’ shear-induced particle migration model, coupled to\udthe Quemada viscosity model, was employed to simulate the macroscopic\udbehaviour of RBCs in four patient-specific geometries: a normal abdominal\udaorta, an abdominal aortic aneurysm (AAA), a normal carotid bifurcation\udand a stenotic carotid bifurcation. Simulations show a migration of RBCs\udfrom the near-wall region with a lowering of wall haematocrit (volume fraction\udof RBCs) on the posterior side of the normal aorta and on the lateralexternal\udside of the iliac arteries. A marked migration is observed on the\udouter wall of the carotid sinus, along the common carotid artery and in\udthe carotid stenosis. No significant migration is observed in the AAA. The\udspatial and temporal patterns of wall haematocrit are correlated with the\udnear-wall shear layer and with the secondary flows induced by the vessel\udcurvature. In particular, secondary flows accentuate the initial lowering in\udRBC near-wall concentration by convecting RBCs from the inner curvature\udside to the outer curvature side. The results reinforce data in literature showing\uda decrease in oxygen partial pressure on the inner curvature wall of the\udcarotid sinus induced by the presence of secondary flows. The lowering of\udwall haematocrit is postulated to induce a decrease in oxygen availability\udat the luminal surface through a diminished concentration of oxyhaemoglobin,\udhence contributing, with the reported lowered oxygen partial pressure,\udto local hypoxia