Understanding the Doppler RI: impact of renal arterial distensibility on the RI in a hydronephrotic ex vivo rabbit kidney model.

Abstract

The aim of this study was to evaluate the influence of elevated ureteral pressure on renal arterial distention, and thereby on the Doppler resistive index. Seven isolated rabbit kidneys were subjected to a pulsatile perfusion while the renal pelvis was pressurized via the ureter. Renal vascular pressure, flow, resistance (pressure/flow) and conductance (flow/pressure) were compared to simultaneous resistive index measurements using linear regression analysis. Changes in the Conductance Index (systolic conductance ‐ diastolic conductance/systolic conductance) were likewise compared to the resistive index. Elevations in ureteral pressure were significantly correlated with (1) increased resistive index values, (2) increased mean renal vascular resistance, (3) decreased mean conductance, and (4) increased conductance index values (for all correlations P < 0.05). The increases in the resistive index correlated significantly with increases in the conductance index. This study shows that elevated ureteral pressure, likely acting via interstitial pressure, diminishes the conductance of the renal vascular bed. Because this effect is more dramatic at diastole, the cyclic patterns of flow are altered, resulting in elevated resistive index values. The results indicate the importance of the interaction between vascular distensibility and pulsatile flow, rather than overall mean renal vascular resistance, in determining resistive index values.

Evidence for Abundant Presence of Chymase-Positive Mast Cells in the Kidneys of Patients with Immunoglobulin A Nephropathy: Effect of Combination Therapy with Prednisolone and Angiotensin II Receptor Blocker Valsartan

“…Renal circulation cannot be directly assessed in humans, but renal flow in interlobular arteries can be evaluated using RI and Doppler sonography (13,16). This method provides an indirect indication of blood flow and therefore may be somewhat variable, although we obtained good reproducibility for day-to-day measurements (see Methods).…”

Acute kidney injury in the perioperative period and in intensive care units (excluding renal replacement therapies)

“…The first is the significance of the resistive index values and variations, which remains unclear because the relationship between this parameter and renal vascular resistances seems to be poor, perhaps due to a large number of additional factors implicated in AKI [38,39,[53][54][55][56]. Indeed, experiments performed on models of ex vivo kidneys have confirmed a major role for vascular compliance (modification in vascular diameter following changes in pressure) or pulse pressure as a determinant of the resistive index [54][55][56]. These experimental data have been recently confirmed in kidney-transplanted patients [57].…”

Renal resistive index and low-grade inflammation in patients with essential hypertension

“…In fact, elevations in hsCRP have been associated with reduced arterial elasticity 27 and increased arterial stiffness measured by pulse wave velocity (PWV), 28,29 and the relationship between hsCRP and IMT as an early marker of atherosclerosis was shown. 30,31 Moreover, a strict dependence of RRI from arterial stiffness was demonstrated in experimental studies, 8,26 and an association was confirmed between RRI and PP, 21,[32][33][34][35] and between RRI and PWV. 33,36 A relationship between RRI and IMT was also reported.…”

“…In fact, tubules and interstitium, rather than glomerular capillaries, are considered to constitute the initial site of kidney injury, 25 and a common feature of experimental models of salt-sensitive hypertension is the existence of tubulo-interstitial inflammatory infiltration, in addition to intrarenal arteriolopathy. 13 In particular, the experiment by Murphy et al 26 showed 21 (33) 8 (38) 13 (31) 16 (37) Ca-channel blockers (n (%)) 6 (9) 3 (14) 4 (10) 5 (12) Diuretics (n (%))…”