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Fig. 5. —Diagram shows how ureteral pressure affects systolic and diastolic blood flow in larger renal arteries typically insonated during clinical renal Doppler studies. Each section of figure shows Doppler gate in conduit (segmental or arcuate) artery, which branches into smaller compliant vessels downstream. Length of arrow in Doppler gate represents velocity of blood flow. As shown in Figure 4, changes in ureteral pressure (0 mm Hg in A and B; 60 mm Hg in C and D) significantly affect arteriolar cross-sectional areas and thus total blood flow volume. In less compliant, larger conduit arteries, these changes in blood flow are manifested as cyclic changes in blood velocity. Thus, relative increase in velocity that occurs at systole (measured using resistive index) is greater when ureteral pressure is elevated (velocity in A > B, but C >> D). (Reprinted with permission from [94])