Radial distribution of the Doppler power from porcine blood over a pulsatile flow cycle

The Doppler power from porcine blood in a mock flow loop was observed to vary spatially and temporally during a pulsatile cycle. It was found to decrease with shear rate under steady flow, except near the center of the tube where other mechanisms such as radial distribution of the rouleaux across the tube might be involved. The Doppler power varied with stroke rate at the center of the tube in a way of such that the peak of the Doppler power was closer to the peak systole from 20 to 60 beats/min (BPM) and the power and velocity peaks coincided at 60 BPM. The coincidence of the Doppler power peak with the flow peak may be speculated to result from the aggregation enhanced by acceleration and the dynamic interactions of the rouleaux during a cycle. The 'black hole' phenomenon was observed over portions of the flow cycle. All these complex variations across the tube over a cycle are thought to be due to red cell aggregation, which can be affected by shear rate, acceleration, and radial position.