Renal pressure-flow relationship and renin activation in a porcine model comparing unilateral and bilateral renal artery stenosis.

Because renal artery stenosis (RAS) often presents bilateral, we sought to investigate the renal pressure-flow relationship and its relation to renin release, in the presence of a contralateral significant stenosis. A porcine model of graded unilateral RAS in the presence of a significant contralateral stenosis was created. The severity of the stenosis was expressed as the ratio between distal renal pressure (P_d) and aortic pressure (P_a). P_d and renal flow velocity were continuously measured using a combined pressure-flow wire (Combowire®). Hemodynamic measurements and blood sampling for renin, angiotensin, and aldosterone were performed in baseline conditions and during progressive balloon inflation in the renal artery leading to stepwise 5% P_d decrements. Resistive index (RI) was computed as (1-(End Diastolic V/Maximum Peak Systolic V))*100. A decrease of average peak flow velocity (APV) was observed when distal renal perfusion pressure decreased by 25% and was associated with activation of renin secretion. The RI decreased already for minimal changes in P_d/P_a ratio. In an animal model of unilateral graded RAS in the presence of a significant contralateral stenosis, a 25% decrease in perfusion pressure results in a significant decrease in distal renal flow, causing a more pronounced upregulation of renin secretion when compared to a model of graded unilateral RAS without contralateral significant RAS.