Effect of downstream cross-sectional area of an arterial bed on the resistive index and the early systolic acceleration

PURPOSE: To evaluate the effect of the increase in total cross-sectional area of arteries as they branch beyond the main trunks on the resistive index (RI)and early systolic acceleration (ESA). MATERIALS AND METHODS: An essentially noncompliant in vitro model that used a pulsatile pump, blood-mimicking fluid, and a branching tubing network that could be configured to produce a downstream cross-sectional area one, two, four, or eight times that of the feeding vessel was used to investigate the relationship, if any, between arterial bed cross-sectional area and the RI and ESA. RESULTS: The mean ESA in the branching network was inversely proportional to cross-sectional area, decreasing by approximately a factor of two for every doubling of the cross-sectional area. The mean RI in the branching network decreased with increasing cross-sectional area, but not as greatly as the ESA did; the mean RI in the bed with eight times the upstream cross-sectional area had an RI that was,approximately three-fourths the upstream RI. These relationships are real, as the slopes of the plots (ESA vs cross-sectional area, P =.001; RI vs cross-sectional area, (P <.02) are significantly different from zero. CONCLUSION: RI and ESA decrease as a result of increasing downstream cross-sectional diameter of the arterial bed.