The effect of hemodynamics, vessel wall compliance and hematocrit on ultrasonic Doppler power: an in vitro study.
Previous in vitro studies in rigid tubes under pulsatile flow conditions have reported a lack of a cyclic variation in blood echogenicity that contradicts in vivo results. To investigate whether or not these variations can be attributed to the compliance of the vessel wall, a series of in vitro experiments with compliant tubes, under pulsatile flow conditions, was performed. Two important factors that may affect the Doppler power were investigated: 1. the dependence on hematocrit and 2. the effect of the vessel wall elasticity. In the present study, it is shown that, at the low beat rates, the peak of the mean Doppler power within the flow cycle depends on the vessel wall compliance. 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 that is more evident in compliant vessels. At a higher pulsation rate of 37 beats/min, a different variation is observed. A drop in the power occurs near peak systole in compliant tube experiments and is more pronounced as the vessel becomes more constricted. The observed power drop agrees with previously reported in vivo results, but is not seen in rigid tube experiments. The results of this study suggest that proper interpretation of cyclic variations in Doppler power requires a knowledge of hemodynamic parameters, such as the modulus of elasticity of the vessel wall, propagation velocity or, possibly, the phase angle of input impedance.
Missaridis
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TX
Bioengineering Program, The Pennsylvania State University, University Park 16802, USA.
Shung
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KK
D000818:Animals; D003187:Compliance; D005583:Fourier Analysis; D006400:Hematocrit; D006439:Hemodynamics; D066298:In Vitro Techniques; D019047:Phantoms, Imaging; D011673:Pulsatile Flow; D013552:Swine; D013997:Time Factors; D018608:Ultrasonography, Doppler / Q000295:instrumentation / Q000379:methods* / Q000706:statistics & numerical data; D018924:Vascular Capacitance; D014655:Vascular Resistance