Size determination of red blood cell aggregates induced by dextran using ultrasound backscattering phenomenon

Different methods are commonly used to study the red blood cell aggregation phenomenon. The major interest of the ultrasonic method presently discussed is to assess the mean size of red blood cell (RBC) aggregates by measuring ultrasonic intensity backscattered by blood. Applying Rayleigh theory of sound to blood medium, one can show that the scattered ultrasonic intensity is proportional to the 6th power of the size of the RBC aggregates. The ultrasonic method is used to evaluate the mean size of RBC aggregates induced by dextrans. RBCs are suspended at various hematocrits H, in solution of dextrans of different molecular weights M and at different weight concentrations C_w. Results are presented by using the ultrasonic backscattering coefficient χ which is a relevant quantity in a scattering experiment. For suspensions of RBCs aggregated with dextran of molecular weight 70 000 dalton (dextran 70) at concentration C_w = 40 g/l, variations of χ as a function of H are similar to those obtained for normal blood. At a fixed hematocrit, variation of χ versus C_w for dextran 70 exhibits a maximum at 40 g/l. In the case of RBCs suspended at hematocrit 20 % and aggregated with dextrans of molecular weight M, 70 000 ⩽ M ⩽ 2 000 000, the variations of χ versus molar concentration Cm are similar to those of the microscopic aggregation index defined by Chien (1). Finally, a statistical model of the blood structure previously described (2) is applied to evaluate the mean size of the aggregates. According to this model, the mean size of aggregates is independent of hematocrit for H ⩽ 40 % and independent of the molecular weight of dextran for M ⩾ 150 000 dalton.