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.
In order to determine if dynamic positron emission tomography (PET) and N-13 ammonia can be used to quantitate regional RBF (rRBF) noninvasively, six anesthetized dogs were examined with PET imaging after an iv bolus administration of 5 mCi of N-13 ammonia. Renal time activity curves and the arterial input function were derived from regions of interest drawn over the renal cortex and abdominal aorta, respectively. For calculation of rRBF, less than 120 s of the initial data were used to minimize contamination by plasma metabolites of N-13 radioactivity. rRBF was quantitated with a two-compartment model, and the results were compared with simultaneously acquired microsphere blood flow measurement. Fourteen experiments were performed in six dogs, and four regions of interest on renal cortex were selected on each PET image. RBF derived from dynamic PET imaging with N-13 ammonia was linearly related to microsphere (MS) values (rRBF = 1.06 x MS - 0.17; r = 0.91). Mean rRBF in the canine experiments was 4.0 mL/min/g. The results indicate that dynamic N-13 ammonia renal PET can provide noninvasively quantitative rRBF.
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