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 ar ea 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 th at could be configured to produce a downstream cross-sectional area one, tw o, 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 t o cross-sectional area, decreasing by approximately a factor of two for eve ry doubling of the cross-sectional area. The mean RI in the branching netwo rk decreased with increasing cross-sectional area, but not as greatly as th e ESA did; the mean RI in the bed with eight times the upstream cross-secti onal area had an RI that was,approximately three-fourths the upstream RI. T hese relationships are real, as the slopes of the plots (ESA vs cross-secti onal 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.