Adjusted resistive index: a method to estimate rapidly renal blood flow: preliminary validation in hypertensives

Abstract

The Doppler Rl, measured in a blinded fashion, was correlated with RBF, RVR, and GFR calculated by simultaneous clearance measurements. Nine hyper• tensive patients were studied weekly while receiving increasing doses of the vasodilator minoxidil. In 36 studies, RI was significantly correlated with RBF (r = were adjusted for ERV, correlations strikingly improved and were further improved by adjustment for pulse pressure. The ARI allowed semiquantitative predictions of RBF and RVR more accurately than blood urea nitrogen or serum creatinine levels. Cor· relation with GFR was weak. KEY WORDS: Doppler Ultrasonography; Blood flow; Kidneys. over a period of 1.5 to 3 hours.t We postulated that the Doppler RI could be useful as a rapid noninvasive estimation of RBF and RVR.-The Doppler estimation of resistance is based on a relative decrease in diastolic velocity compared to systolic velocity seen with increasing vascular resistance. The RI is a mathematical model for resistance in which the difference between systolic and diastolic Doppler frequency shifts is divided by the systolic shift (lsystolic·diastolic]/systolic). As resistance increases, the diastolic proportion decreases and the index value increases, reaching 1.0 when diastolic flow ceases. In vitro and in vivo animal studies have demonstrated strong correlation between RBF, RVR, and Doppler Rl. 2 ·3 The quantitative relationship of Doppler RI to RBF, RVR, and GFR has not been previously studied in humans, however. To determine if RI type measurements could provide quantitative estimates of these hemodynamic pa· rameters, we studied the correlation of RI measurements with RBF, RVR, and GFR values calculated by simultaneous inulin and para-aminohippurate clearance.

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

“…Up to now, it has been largely accepted that elevated RI values, whether due to obstruction or intrinsic renal disease, are due to increased renal vascular resistance. 1,2,[6][7][8]11,[16][17][18] It has been this largely assumed relationship that has provided the theoretical framework supporting the use of Doppler technique in the evaluation of renal disease. However, previous work in our laboratory, using a nonobstructed isolated perfused rabbit kidney model, demonstrated only marginal increases in the RI with high grade (and nonphysiologic) pharmacologically induced vasoconstriction.…”

“…As suggested by its name, the RI is generally considered to reflect RVR. 1,2,[6][7][8]11,[16][17][18] In its classic sense, RVR refers to the mean renal resistance, averaging together any transient systolic-diastolic differences in resistance. However, using an isolated perfused rabbit kidney model, we recently showed that changes in mean RVR have relatively little influence on RI values.…”

A Randomized Unblinded Pilot Study Comparing Albumin Versus Hydroxyethyl Starch in Spontaneous Bacterial Peritonitis * #

“…It was defined as peak systolic frequency shift Ϫ minimum diastolic frequency shift/peak systolic frequency shift and determined from the Doppler waveform by hand measurement with a caliper obtained in the arcuate arteries of the right and left kidney. 24,25 The RI for each patient was calculated as an average value obtained from one measurement recorded in each kidney. Normal values are below 0.7.…”

Comparison of Systemic and Renal Hemodynamics Measured by Doppler Ultrasonography in Canine Experimental Hypovolemia.

“…The recovery of MAP, CO and RBF was caused in this experiment by the reinfusion of a certain volume of blood (30 ml/kg/60 min). In this recovery condition, the autoregulation mechanism for peripheral blood pressure in the kidney may have acted earlier, because MAP increased to approximately 90 mmHg immediately before the recovery of blood circulation [11,27,35]. The increase of the Vmax was recognized as the recovery of the renal blood flow.…”

“…The sample point size was 1 mm in length. The measurements included systolic maximal velocity (Vmax), diastolic minimal velocity (Vmin), pulsatility index (PI), resistance index (RI) and renal blood flow (RBF) in the main renal artery as well as PI and RI in the interlobar artery [5,9,17,18,35].…”