Radial dispersion of red blood cells in blood flowing through glass capillaries: The role of hematocrit and geometry

The flow properties of blood in the microcirculation depend strongly on the hematocrit (Hct). microvessel geometry. and cell properties. Previous ill vitro studies have measured the radial displacement of red blood cells (RBCs) at concentrated Suspensions using conventional microscopes. However, to measure the RBSs motion they used transparent suspensions of ghost red cells. which may have different physical properties than normal RBCs. The present Study introduces a new approach (confocal micro-PTV) to measure the motion of labeled RBCs flowing in concentrated Suspensions of normal RBCs. The ability of confocal systems to obtain thin in-focus planes allowed US to measure the radial position of individual RBCs accurately and to consequently measure the interaction between multiple labeled RBCs. All the measurements were performed in the center plane of both 50 and 100 mu m glass capillaries at Reynolds numbers (Re) front 0.003 to 0.005 using Hcts front 2% to 35%. To quantify the Motion and interaction of multiple RBCs, we used the RBC radial dispersion (D-yy). Our results clearly demonstrate that D-yy strongly depends on the Het. The RBCs exhibited higher D-yy at radial positions between 0.4 and 0.8 R and lower D-yy at locations adjacent to the wall (0.8-1 R) and around the middle of the capillary (0-0.2 R) The present work also demonstrates that D-yy tends to decrease with a decrease in the diameter. The information provided by this study not only complements previous investigations oil microhemorheology of both dilute and concentrated Suspensions of RBCs. but also shows the influence of both Hct and geometry on the radial dispersion of RBCs. This information is important for a better Understanding of blood mass transport mechanisms under both physiological and pathological conditions. (C) 2008 Elsevier Ltd. All rights reserved.