An in vitro study of the effects of Doppler angle, fibrinogen, and hematocrit on ultrasonic Doppler power

For a better understanding of the relationship between the Doppler power an d erythrocyte aggregation of whole blood under steady Row in a conduit, the effects of Doppler angle, fibrinogen concentration, and hematocrit were in vestigated in a mock Row loop. The results show that, at a mean shear rate of 102 s(-1), there was minimal angular dependence; but at a mean shear rat e of 52 s(-1), there was a weak angular dependence as the Doppler angle was varied from 40 degrees to 70 degrees. These results suggest that there was , perhaps, no or little alignment of the red cell aggregates at high shear rates. The Doppler power was found to increase nonlinearly as the fibrinoge n concentration was increased; and the effect of other plasma proteins on r ed cell aggregation may not be negligible, although fibrinogen is the domin ant factor. The results show that the variation of the Doppler power over t he lumen is hematocrit dependent for hematocrits below 26%.