This abstract differs from that originally published in Biorheology 12, 81, 1975.
The resistance to flow of 30% Hct. human red cell suspensions through capillary slits of 25 and 100μm gap and through tubes of 400μm and 1 mm diameter was measured in a constant flow rate microcapillary viscometer which could be set at flow rates corresponding to apparent shear rates at the wall (ASAW) from 20 sec−1 to 1000sec−1. Suspending media were (1) 0.9% NaCl, (2) 3.5% Dextran 40 in 0.9% NaCl and (3) 2% Dextran 200 in 0.9% NaCl. Rouleau formation was marked in medium (3) and negligible in media (1) and (2). Media (2) and (3) were isoviscous. At ASAW 1000 sec−1ηr was the same in media (2) and (3); at ASAW 20 sec−1ηr, was significantly lower in medium (3) than in either (1) or (2) for all capillaries but the lowest value was in the 100 μm slit and the highest in the 1 mm tube. It is concluded that rouleau formation reduces resistance to flow in unbranched capillary channels with diameters from 25 to 400 μm; markedly in a 100μm channel and slightly in a 1 mm channel.
