STUDY OF RED-CELL AGGREGATION IN PULSATILE FLOW FROM ULTRASONIC DOPPLER POWER MEASUREMENTS

Human red cell aggregability and disaggregability represent important hemorheological parameters of blood. Several techniques have been prop osed to evaluate the tendency of red cells to form aggregates and to d isrupt in the presence of shear stress. One of the most recent approac hes is based on the characterization of the intensity of ultrasonic sc attered signals. A pulsatile flow loop model is used in the present st udy to demonstrate the potential applicability of Doppler ultrasound t o detect and characterize the hemodynamic behavior of red cell aggrega tes. Porcine whole blood specimens collected from 20 different pigs we re circulated in the flow model (tube diameter of 0.476 cm) at differe nt mean velocities and pulsation rates. At a pulsation of 70 beats/min for mean velocities of 13 cm/sec and 63 cm/sec, no cyclic variation o f the Doppler power was observed, suggesting the absence of rouleaux b uild-up and rouleaux disruption. At a pulsation of 20 beats/min and me an velocities of 11 cm/sec and 38 cm/sec, statistically significant cy clic variations (p < 0.01) were measured. It is suggested that aggrega te size enlargement, rouleaux orientation with the flow field and the effect of shear stress on rouleaux disruption are possible causes for the observed cyclic variation of the Doppler power within the flow cyc le at a pulsation of 20 beats/min. A discussion of the potential appli cation of this technique for in vivo study in large vessels is given.