CYCLIC VARIATION OF DOPPLER POWER FROM WHOLE-BLOOD UNDER PULSATILE FLOW

The echogenicity and Doppler power from whole blood under pulsatile fl ow have been found to vary during the flow cycle in previous studies b oth in vitro and in vivo, The present study was undertaken to better u nderstand this phenomenon, Doppler power from whole blood under pulsat ile flow was measured with a pulsed Doppler flowmeter as a function of the flow cycle, radial position and compliance of the vessel in a moc k flow loop, It was found that the cyclic variation is more pronounced if the stroke rate is less than 56 beats/min and that the peak of the Doppler power from whole blood flowing near the center stream coincid ed with the peak of the flow velocity, However, it began to lead the v elocity peak as the measurement site was moved away from the center st ream, The lead increased as the radial distance was increased, The res ults also show that the compliance of the vessel can affect, to a cert ain extent, the magnitude of the cyclic variation, Results from intrav ascular Doppler measurements rule out the possibility that the cyclic variation is primarily due to the variation in attenuation caused by v essel wall during a flow cycle.