Effect of distal resistance on Doppler US flow patterns

Abstract

Purpose: To quantify the effect of distal resistance on arterial flow patterns.

Materials and methods: Spectral Doppler tracings were obtained from the suprarenal aorta, infrarenal aorta, and proximal renal arteries of 10 volunteers and from the common, internal, and external carotid arteries (CCA, ICA, and ECA, respectively) of 31 volunteers. Early systolic acceleration (ESA), peak systolic velocity (PSV), end diastolic velocity (EDV), and waveform morphology were evaluated. An in vitro flow model of a compliant vessel in a branched pattern was created to simulate the renal and carotid circulations.

Results: ESA and PSV were significantly lower in the renal artery than in the suprarenal aorta (P < .01). ESA decreased significantly from the CCA to the ICA (P < .001) but only minimally from the CCA to the ECA (P > .20). EDV increased slightly from the CCA to the ICA but decreased substantially in the ECA. As distal resistance was increased in the in vitro model, ESA was more rapid, systole was shortened, EDV was decreased, and PSV was increased.

Conclusion: As blood flows into the low-resistance renal artery or ICA, antegrade flow is shifted into the latter portion of the cardiac cycle, resulting in apparent prolongation of systole and forward flow throughout diastole. As blood flows into the higher-resistance ECA, diastolic flow is diminished. The in vitro model reproduces these Doppler flow patterns by means of manipulation of distal resistance.