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Fig. 4. —Diagram shows how ureteral pressure affects mean, systolic,
and diastolic cross-sectional areas of renal arterioles. Area of compliant
vessels is determined by transmural pressure (intraarterial pressure –
interstitial pressure). Interstitial pressure is almost zero in absence of
ureteral pressure (left half of diagram). During diastole, cross-sectional
area of vessel is relatively large (B), and some additional distention occurs
during systole (A). High ureteral pressures increase interstitial pressure
(right half of diagram). In this setting, arteriole is almost occluded during
diastole because transmural pressure is so low (D), but significant distention
still occurs during systole (C). Although mean cross-sectional area is
markedly smaller with high ureteral pressures (mean conductance of C and D, A
and B), relative distention that occurs during systole is greater (conductance
of A > B, but C >>D). These cyclic changes in cross-sectional area
are underlying cause for parallel changes in total renal conductance (flow /
pressure). (Reprinted with permission from
[94])