Defining Hemodynamic Significance of Renal Artery Stenosis: Insights From a Porcine Model of Graded Renal Artery Stenosis

To investigate the renal pressure-flow relationship and its relation to renin release, because the renal perfusion pressure below which renal flow starts to decline and renin secretion is upregulated is unclear.A porcine model of graded unilateral renal artery stenosis was created. The severity of the stenosis was expressed as the ratio between distal renal pressure (Pd) and aortic pressure (Pa). Pd 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 Pd decrease per 5% increment. Resistive index (RI) was computed as (1 - (End Diastolic V/Peak Systolic V))*100.For a 5% decrease in renal perfusion pressure (95% of aortic pressure or 5% decrease compared to Pa), peak systolic velocity started to decrease. A significant decrease in average peak flow velocity was observed when distal renal perfusion pressure decreased by 25% and was associated with activation of ipsilateral renin secretion. The RI decreased already for minimal changes in Pd/Pa ratio.In an animal model of unilateral graded renal artery stenosis, a 25% decrease in perfusion pressure results in a significant decrease in distal renal flow, causing upregulation of renin secretion.