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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 nonstenotic 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 Atand 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 nonstenotic 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.

Objective To compare the accuracy of four echo-Doppler-derived velocimetric indices (pulsatility and resistance indices, acceleration and acceleration time) in detecting renal artery stenosis in hypertensive patients. Patients and methods In 73 hospitalized patients with moderate-to-severe hypertension, 18 of whom had normal renal arteries and 55 renal artery stenosis (50-95%) either atherosclerotic (30 cases, five bilateral) or fibromuscular dysplasia (25 cases, two bilateral), we measured the four velocimetric indices using the lateral abdominal approach and sampling Doppler waveforms distally to the stenosis. The diagnostic accuracy of each index was calculated using as cut-off limit the ideal threshold determined with the receiver-operating characteristic curves. Results On average all of the indices were altered significantly in arteries with stenosis of both aetiologies with respect to normal arteries, the alterations of pulsatility and resistance indices being, however, less pronounced than those of acceleration and acceleration time, particularly in atherosclerotic stenosis. With the cut-off limits of 0.93, 0.59 and 7.4 m/s2 and 60 ms, respectively, for pulsatility and resistance indices, acceleration and acceleration time, their diagnostic accuracies were 80, 73, 93 and 92%. In stenotic arteries, only the acceleration time was correlated with the degree of arterial narrowing, whereas, in normal arteries, only pulsatility and resistance indices were directly correlated with the age of patients. Conclusions Acceleration and acceleration time are more accurate indices than pulsatility and resistance to screen for renal artery stenosis, probably because their alterations are less attenuated by the counterbalancing effects of age and of atherosclerosis.