Usefulness and limits of distal echo-doppler velocimetric indices for assessing renal hemodynamics in stenotic and non-stenotic kidneys

Background: Distal echo-Doppler velocimetric indices are widely used for revealing the presence of a renal artery stenosis but there is scarce information as to whether they reflect the renal hemodynamics in stenotic and non-stenotic kidneys. Objectives and methods: We evaluated the pulsatility and resistive indices (PI and RI), acceleration (A) and acceleration time (At) and correlated their values with those of effective renal plasma flow (ERPF), glomerular filtration rate (GFR), renal vascular resistance (RVR) and filtration fraction (FF) estimated by single kidney scintigraphy in 24 kidneys with 70-95% renal artery stenosis (atherosclerotic n = 17, fibromuscular n = 7) and in 27 non-stenotic kidneys (11 contralateral to renal artery stenosis and 16 of patients with essential hypertension). In patients with stenotic kidneys, these measurements were repeated within 7 days after a successful percutaneous transluminal renal angioplasty (PTRA) (in 11 arteries performed in combination with stent implantation). Results: Prior to dilation we found that the stenotic kidneys had significantly lower values of ERPF, GFR and higher RVR than the non-stenotic kidneys and that these hemodynamic alterations were associated with those, also statistically significant, of the four velocimetric indices. In non-stenotic kidneys, there were highly significant relationships between PI and ERPF, and RVR (r= -0.68 and 0.81 respectively P <0.01); similar relationships were found for RI (r= -0.67 and 0.78 P <0.01) whereas no such correlations were found between these two velocimetric indices and GFR and FF; also no correlations were found between A and At and ERPF, GFR, RVR and FF. In stenotic kidneys no significant correlations were found between any of the velocimetric and the hemodynamic indices. Renal artery dilation induced clear cut increments in ERPF, GFR and reduction in RVR in post-stenotic kidneys, which were associated with normalization of all four velocimetric indices. No relationships were observed between the renal hemodynamic and the velocimetric changes induced by dilation; however in post-stenotic kidneys the relationships between PI and RI, ERPF and RVR were restored as in non-stenotic kidneys. Conclusions: These data indicate that PI and RI can be used to assess ERPF and RVR both in non-stenotic and post-stenotic kidneys; however, none of the velocimetric indices examined in this study can provide valid informations on the renal hemodynamics of stenotic kidneys and on their changes induced by PTRA.