Comparison of new ultrasound index with laser reference and viscosity indexes for erythrocyte aggregation quantification

We have previously established new ultrasonic indexes for erythrocyte aggregation using a Couette device, and validated them toward the Rayleigh's theory and reproducibility. Two hydrodynamic protocols were applied on various suspensions and their aggregation degrees were characterized by: 1. for the decreasing shear rates protocol: the power P_US at the nominal frequency of the transducer used; 2. for the kinetic protocol: aggregation times (latency and half-rise times), variation between initial desaggregated state (Vo) and final aggregated state (V_inf) and AI_US, which is the integral of the kinetic curve over time. The objective of the present study was to demonstrate the ability of these indexes to characterize the aggregation dynamics of suspensions with various levels of aggregation induced by concentrations of dextran 70 kD (Dx) of 10, 20 and 40 g/L added to washed red cells resuspended in saline solution. The results showed a maximum of backscattered power (P_US) for Dx = 40 g/L with the decreasing shear rates protocol. We measured a final aggregation level (V_inf), a minimal aggregation time (T_m) and a maximal value of AI_US for Dx = 40 g/L with the aggregation kinetics protocol. On the other hand, viscosity is increased with dextran concentration. These evolutions of the ultrasound (US) indexes and viscosity with dextran concentrations are consistent with litterature reports. In addition, a particularly interesting phenomenon of US backscattering enhancement was observed for kinetics with no null final shear rate, which has never before been reported in such a precise manner. By another way, each of the dextran suspensions was tested on the laser erythroaggregometer that is presently considered as the "gold standard" method for eythrocyte characterization. The laser indexes (aggregation time T_a, aggregation indexes AI_10s and AI_60s), deduced from a kinetic protocol, have similar significance to the US ones. Statistical comparisons have been done between laser and ultrasonic indexes and significant correlations (0.001 < p < 0.01) were obtained. The set of results allowed us to conclude that ultrasonic indexes are suitable markers for the erythrocyte aggregation.