Distribution of dog erythrocyte density and relationship to cell suspension viscosity

An experimental investigation was undertaken to determine the density of young and old dog erythrocytes and the viscosity of suspensions prepared from these erythrocyte fractions. The densities of young and old RBC from three dog donors were determined from direct measurements of post-centrifugation cell fraction weight and volume. The density distribution range of young erythrocytes was found to vary from 1.035 g/ml to 1.088 g/ml. Meanwhile, the density of distribution range of old erythrocytes varied from 1.073 g/ml to 1.105 g/ml. The average density of old RBC was found to be about 1.0-1.5 % higher than that of young RBC in agreement with earlier studies. The average density of RBC obtained from the three donor dogs was 1.074 g/ml. For young and old erythrocyte suspensions, viscosity was measured in a cone and plate viscometer at two shear rates (150 sec- 1 and 225 sec- 1) and for measured Ht values ranging from 20% to 50%. Dog erythrocyte suspension viscosity determinations with measured hematocrit (Ht) and shear rate parameters yielded a non-linear relationship for a hematocrit range of 20% to 50%. The viscosity values of suspensions of both young and old erythrocytes ranged from 2.30 cP to 5.53 cP at 25-27 °C. When these results were compared with available data for human blood, it was found that dog erythrocyte suspensions were slightly more viscous than those of human blood erythrocyte suspensions at the same Ht and shear rate values and temperature. The viscosity of old erythrocyte suspensions was found to be slightly higher than that of young erythrocyte suspensions at shear rates of 150 sec- 1 and of 225 sec- 1. This result suggests that old erythrocytes are less flexible than young erythrocytes. The average blood viscosity value for a shear rate of 150 sec-1 was 5-9% higher than for a shear rate of 225 sec- 1. The research performed using dog erythrocytes agrees with the earlier work with human blood and demonstrates that suspensions of older RBC have viscosities greater than those of younger RBC at the same hematocrit value. This result suggests that there may be significant effects on blood flow in normal and disease states when the average age of RBC is altered from a normal distribution. Additional research will be needed to improve the quantification of RBC age effects on blood flow properties and to establish the possible relevance of these effects on conditions of health and disease in humans and animals.