Osmolality- and hematocrit-mediated flow behavior of RBC suspensions in 33 micrometer ID tubes

The effects of suspending medium osmolality (166 to 736 mosm/kg) on relative viscosity (eta r) and tube hematocrit (HT) measured in 33 microns diameter tubes were studied for 40, 47 and 57% feed hematocrit (HF) suspensions of human RBC in buffer. At all feed hematocrits, eta r increased sharply for the hypertonic media, but was essentially insensitive to hypotonicity. HT/HF was less affected by osmolality (13% change over the entire range of osmolality and feed hematocrit). Viscosities could not be calculated from the experimental HT values. However, eta r could be predicted from RBC number concentration and the tube diameter/RBC volume ratio via a semi-empirical model. RBC transport efficiency depended on both feed hematocrit and osmolality, and was maximal at or near isotonic conditions. Our results appear applicable to non-isotonic regions of the microcirculation, and to estimation of flow resistance for RBC with abnormal cellular mechanical properties.