The normal range of Doppler findings in native kidneys has not been studied extensively. This study correlates changes in Doppler resistive index (RI) Doppler arterial waveform analysis is based on the changes in flow velocity created by pulsatile arterial perfusion. The ratio of systolic to diastolic velocity is determined in large part by downstream resistance . 16 With increasing resistance, the diastolic velocity falls relative to the systolic value. The resistive index was designed as a mathematical index proportional to ar· terial resistance, and it equals the peak systolic frequency shift minus the peak end-diastolic shift divided by the peak systolic shift. MATERIALS AND METHODSThis study consisted of two series of patients. In a small preliminary investigation, measurements were made to determine the spatial and temporal variability of serial waveforms obtained on a given kidney. Information from this pilot study was used to develop an efficient examination technique for the second, larger clinical study designed to evaluate normal age variation.The preliminary study examined 24 kidneys in 12 patients with no known renal disease. In these patients, three individual waveform measurements were made

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.

Interruption of flow in the vasa vasorum may lead to medial necrosis and aneurysm formation. The purpose of this study was to determine whether angioplasty produces significant alterations in the morphology or blood flow of the vasa vasorum of the dilated artery. The morphology of the canine vasa vasorum was studied before and after angioplasty; in a separate experiment vessel wall blood flow (VWBF) in canine carotid arteries was measured after angioplasty to determine whether physiologic regulation of the blood flow was disrupted by arterial dilation. No morphologic changes could be demonstrated in the vasa vasorum of the dilated artery; however, VWBF was increased by 1194 +/- 215% (mean +/- standard error, p less than 0.01) between 90 and 120 minutes after angioplasty. VWBF in the adjacent nondilated arterial segment was also increased (720 +/- 177% between 10-30 minutes, p less than 0.01) but returned toward normal after 60 minutes. Adenosine caused a "paradoxical" decrease in VWBF (p less than 0.05) of the dilated arterial segment while causing increased VWBF (p less than 0.05) in the thoracic aorta. Angioplasty appears to produce persistent hyperemia in the dilated arterial wall. A paradoxical response to adenosine suggests that vasa vasorum in the dilated arterial segment are maximally vasodilated. This may be due to mechanical disruption of vasomotor tone or to release of vasoactive substances.

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