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.