The effect of hemodynamics, vessel wall elasticity and hematocrit on the ultrasonic Doppler power-an in-vitro study

Two important factors that may affect the Doppler power were investigated: a) the dependence on hematocrit and b) the effect of the vessel wall elasticity. It is shown here, that at low beat rates, the peak of the mean Doppler power within the flow cycle depends on the vessel wall elasticity. When the vessel becomes more compliant, the peak is shifted from the early to the late systole. Additionally, there is a correlation between the power peak and hematocrit, which is more evident in elastic vessels. At a higher pulsation rate of 37 beats/min, a different variation scheme is observed. A drop in the power occurs near peak systole, in elastic tube experiments. This result agrees with previously reported in vivo results. The power drop is amplified as the vessel constriction increases. This result suggests that proper interpretation of cyclic variations in Doppler power requires a knowledge of hemodynamic parameters, such as the modulus of elasticity, propagation velocity or possibly the phase angle of input impedance