The renal resistive index: is it a misnomer?

Abstract

Progress in digital ultrasound technology and diffusion of\ud Doppler ultrasound evaluation of the kidney enable a\ud widespread non-invasive evaluation of renal haemodynamics.\ud Initially most attention has been paid to the study\ud of extraparenchymal renal arteries, mainly to detect renovascular\ud disease. However, this approach has low reproducibility\ud and accuracy. Therefore, interest has gradually\ud moved towards the duplex evaluation of intrarenal anatomy,\ud where the best and most reliable signals are obtained\ud from the large segmental or interlobar arteries that run\ud directly towards the transducer.\ud Among the sonographic parameters used in the last\ud decade, great emphasis has been placed on the intrarenal\ud resistive index (RRI), which is defined as the dimensionless\ud ratio of the difference between maximum and minimum\ud (end-diastolic) flow velocity to maximum flow velocity.\ud It has been used for a long time for the diagnostic and\ud prognostic assessment of renovascular disease . One\ud of the earliest prospective uses of the RRI was in the\ud prediction of kidney function outcomes following intervention\ud for renal artery stenosis. In the pioneering study of\ud Radermacher et al., an RRI[0.80 is associated with poorer\ud outcomes, when surgery or angioplasty is used to correct\ud renal artery stenosis ..

Arterial Hypertension and the Hidden Disease of the Eye: Diagnostic Tools and Therapeutic Strategies

“…Notably, a close association was described between reduced ChT and increased intrarenal resistance index (RRI), which is a marker of impaired intrarenal hemodynamics as well as of extrarenal organ damage [ 73 , 74 , 75 ], being closely associated with carotid intima-media thickness [ 73 ] and with aortic stiffness [ 75 ]. It is well established that large arteries have elastic properties that ensure the dampening of pressure and flow fluctuations generated at every ventricular contraction, in order to protect the microvascular level from elevated PP and from damage due to hyperperfusion.…”

Relationship between kidney findings and systemic vascular damage in elderly hypertensive patients without overt cardiovascular disease

“…Several studies showed the close association between age and the decline of renal function . Similarly, intrarenal hemodynamic alterations, assessed by ultrasonographic intraparenchymal renal resistive index (RRI) and related to systemic vascular changes, were correlated with increasing age in previous studies . However, the prognostic contribution to risk stratification of an increased RRI remains to be demonstrated in elderly patients …”

Renal haemodynamics and coronary atherosclerotic burden are associated in patients with hypertension and mild coronary artery disease

“…Recently, intrarenal haemodynamics were identified as a potential marker of systemic vascular damage (8) and a useful tool to better stratify the short and long-term cardiovascular risk of patients in different clinical subsets. In particular, renal resistance index (RI) and renal pulsatility index (PI), non-invasively assessed by Duplex ultrasound, were closely associated with well-known markers of subclinical organ damage, including carotid intima-media thickness (cIMT) (9-11), arterial stiffness (9,12) and left ventricular mass (13,14). Furthermore, recent studies detected the direct role of intrarenal haemodynamic impairment as an independent predictor of adverse cardiovascular events and mortality in different populations, particularly in the elderly (15) and in patients with chronic kidney disease (CKD), hypertension or heart failure (16)(17)(18).…”