Ultrasonic backscattering from porcine whole blood of varying hematocrit and shear rate under pulsatile flow

It was shown previously that ultrasonic scattering from whole blood varies during a flow cycle under pulsatile flow both in vitro and in vivo. It has been postulated that this cyclic variation may be associated with the dynam ics of red cell aggregation because the shearing force acting on the red ce ll aggregates across the lumen is a function of time during a flow cycle. I n all studies, the local shear rate variation as a function of time Is unkn own, The effect of shear rate on the red cell aggregation and, thus, on ult rasonic scattering from blood can only be merely speculated. One solution t o this problem is to estimate the shear rate in a flow conduit by finite el ement analysis (FEA), An FEA computational fluid dynamics (CFD) tool was us ed to calculate local shear rate in a series of experiments in which ultras onic backscattering from porcine whole blood under pulsatile flow was measu red as a function of hematocrit and shear rate intravascularly with a 10-MH z catheter-mounted transducer in a mock flow loop. The results show that, a t 20 beats per min (BPM), the magnitudes of the cyclic variation for hemato crits at 30, 40, and 50% were approximately 4 dB, However, at 60 BPM, the m agnitude of cyclic variation was found to be minimal. The results also conf irm previous findings that the amplitude and the timing of the peak of ultr asonic backscattering from porcine whole blood under pulsatile flow during a flow cycle are dependent upon the shear rate and hematocrit in a complica ted way. (C) 1999 World Federation for Ultrasound in Medicine & Biology.