Ratio of cells and plasma in blood flowing past branches in small plastic channels

Red cell concentrations related to flow were studied by measuring delivered cell fractions from branching channels. A branched channel in a plastic block was cast by pouring setting plastic into a mold containing two 0.18 mm steel wires; one was beveled and touching, at 60 degrees, the side of the other wire, which extended across the mold. The wires were later withdrawn. Two of these flow chambers were perfused (flow of 0.14 ml/min) with human blood or blood diluted with host plasma (anticoagulant ethylenediaminetetra-acetic acid), and the percent cell volume was measured in the collecting tubes. The difference in hematocrit from the two outflow channels was a linear function of the proportional flow in the side branch, and the average slope for 29 experiments was 32.0 +/- 9.7 (SD)% with a negative dependence on inflow hematocrit (correlation coefficient -0.63, P less than 1%). When analyzed as cell flux ratio vs. flow ratio the data show a significant deviation from the line of identity, which is most marked for the lowest values of hematocrit that we studied (approximately equal to 20%). We concluded that if the model branching channels are representative of arteriolar-sized blood vessels, then there is the potential for wide variations in hematocrit in the microcirculation, especially in blood with a low cellular fraction.