Cyclic variation of Doppler backscattering power from porcine blood in a pulsatile flow model

Measurements made on polystyrene microspheres, porcine red cells suspended in normal saline solution, and porcine whole blood of 4% and 40% hematocrits in a pulsatile mock flow loop model are discussed. Different mean flow velocities and two pulsation rates (20 and 70 beats/min) were investigated. Results on polystyrene microspheres (diameters of 20 to 130 μm) suspended in a mix of saline solution and glycerol show a progressive decrease of the root-mean-square (RMS) power in the accelerating phase of the systolic period, a minimum at peak systole, and an increase during deceleration of flow. Results obtained for red cell suspension exhibit a similar behavior independent of hematocrit. For porcine whole blood, no cyclic variation was observed at high flow velocity and pulsation of 70 beats/min for high hematocrit. However, reducing the pulsation of 20 beats/min gave rise to a significant drop of the RMS power near peak systole. These results suggest that Doppler power from blood is cyclic dependent