Affiliations: Institute for Normal and Pathological Physiology, University of Köln, Germany
Note: [1] Supported by the Deutsche Forschungsgemeinschaft.
Note: [] Invited by: Editor A. Silberberg
Abstract: Phase separation between red cells and plasma were studied using blood perfused model systems which consisted of glass capillaries (I.D. between 3.3 and 11.0 μm) branching from a large bore (I.D. 1.5 mm) feed channel. The orifice of the capillaries was either positioned in the centerline of the feed channel (model A) or flush with its wall (model B). Capillary discharge hematocrit (HD) was measured at different flow conditions and related to the hematocrit in the feed channel (HF). The ratio HD/HF was found to be correlated to the ratio between wall shear stress in the capillary and in the feed channel (τT/τF). While at low τT/τF almost no cells entered the capillary, HD increased with increasing τT/τF and approached HF in model A. In model B, HD did not reach HF within the experimental range of τT/τF’ The flow fractionation in model B can be explained by “plasma skimming”. In model A cell entry into the capillary is determined by the relationship between forces acting on the red cell either in the direction of the feed channel or of the capillary. For this mechanism the term “screening effect” is proposed. This effect decreases with increasing HF and increasing capillary diameter and vanishes when capillary diameter approaches 12 μm.
