Biomedical subjects

S E Rittgers

Publications and source records attributed to S E Rittgers.

At least 19 recordsLinked to original sources

PubMed2001

The persistence of electrostatically seeded endothelial cells lining a small diameter expanded polytetrafluoroethylene vascular graft.

PURPOSE: The purpose of this study was to evaluate the persistence of electrostatically seeded endothelial cells (ECs) lining an expanded polytetrafluorethylene (e-PTFE) graft after one week exposure to in vivo circulation in a canine femoral artery bypass model. This was accomplished by visualizing the PKH 26 (red fluorescent) label placed in the EC membranes prior to the seeding procedure. Furthermore, this study was performed to confirm that the source of the ECs lining the graft were those from the initial inoculum. METHODS: This evaluation consisted of harvesting autologous, canine jugular vein ECs, PKH 26 labeling of the ECs, electrostatic EC seeding the e-PTFE grafts (4mm GORE-TEX, Length=6cm), implanting the grafts (femoral artery model) for one week, and explanting the grafts for light, fluorescent and scanning electron microscopy evaluations of the luminal surface. RESULTS: The unseeded grafts (controls) had a mean fluorescence surface coverage of 6.82 +/- 7.19%, while the EC seeded grafts had a mean of 90.3 +/- 14.3% which is significantly (p <0.001) different from the controls. Overall, the seeding time including the EC harvesting and PKH 26 labeling protocol was approximately 75 min. CONCLUSIONS: The electrostatically seeded ECs persisted after implantation of the graft as demonstrated by the PKH 26 labeling data. The fluorescent data also demonstrated that the neointima formed (EC luminal surface coverage) one week after implantation was in fact derived from the ECs initially seeded as determined by the abundance of the labeled ECs.

Animals↗

PubMed2001

Hemodynamic factors at the distal end-to-side anastomosis of a bypass graft with different POS:DOS flow ratios.

A pulsatile flow in vitro model of the distal end-to-side anastomosis of an arterial bypass graft was used to examine the effects that different flow ratios between the proximal outlet segment (POS) and the distal outlet segment (DOS) have on the flow patterns and the distributions of hemodynamic factors in the anastomosis. Amberlite particles were tracked by flow visualization to determine overall flow patterns and velocity measurements were made with Laser Doppler anemometry (LDA) to obtain detailed hemodynamic factors along the artery floor and the graft hood regions. These factors included wall shear stress (WSS), spatial wall shear stress gradient (WSSG), and oscillatory index (OSI). Statistical analysis was used to compare these hemodynamic factors between cases having different POS:DOS flow ratios (Case 1-0:100, Case 2-25:75, Case 3-50:50). The results showed that changes in POS:DOS flow ratios had a great influence on the flow patterns in the anastomosis. With an increase in proximal outlet flow, the range of location of the stagnation point along the artery floor decreased, while the extent of flow separation along the graft hood increased. The statistical results showed that there were significant differences (p<0.05) for the mean WSS between cases along the graft hood, but no significant differences were detected along the artery floor. There were no significant differences for the spatial WSSG along both the artery floor and the graft hood. However, there were significant differences (p<0.05) in the mean OSI between Cases 1 and 2 and between Cases 1 and 3 both along the artery floor and along the graft hood. Comparing these mechanical factors with histological findings of intimal hyperplasia formation obtained by previous canine studies, the results of the statistical analysis suggest that regions exposed to a combination of low mean WSS and high OSI may be most prone to the formation of intimal hyperplasia.

Anastomosis, Surgical↗

PubMed2001

Intimal hyperplasia and wall shear in arterial bypass graft distal anastomoses: an in vivo model study.

The observation of intimal hyperplasia at bypass graft anastomoses has suggested a potential interaction between local hemodynamics and vascular wall response. Wall shear has been particularly implicated because of its known effects upon the endothelium of normal vessels and, thus, was examined as to its possible role in the development of intimal hyperplasia in arterial bypass graft distal anastomoses. Tapered (4-7 mm I.D.) e-PTFE synthetic grafts 6 cm long were placed as bilateral carotid artery bypasses in six adult, mongrel dogs weighing between 25 and 30 kg with distal anastomotic graft-to-artery diameter ratios (DR) of either 1.0 or 1.5. Immediately following implantation, simultaneous axial velocity measurements were made in the toe and artery floor regions in the plane of the anastomosis at radial increments of 0.35 mm, 0.70 mm, and 1.05 mm using a specially designed 20 MHz triple crystal ultrasonic wall shear rate transducer Mean, peak, and pulse amplitude wall shear rates (WSRs), their absolute values, the spatial and temporal wall shear stress gradients (WSSG), and the oscillatory shear index (OSI) were computed from these velocity measurements. All grafts were harvested after 12 weeks implantation and measurements of the degree of intimal hyperplasia (IH) were made along the toe region and the artery floor of the host artery in 1 mm increments. While some IH occurred along the toe region (8.35+/-23.1 microm) and was significantly different between DR groups (p<0.003), the greatest amount occurred along the artery floor (81.6+/-106.5 microm, mean +/- S.D.) (p < 0.001) although no significant differences were found between DR groups. Linear regressions were performed on the paired IH and mean, peak, and pulse amplitude WSR data as well as the absolute mean, peak, and pulse amplitude WSR data from all grafts. The mean and absolute mean WSRs showed a modest correlation with IH (r = -0.406 and -0.370, respectively) with further improvements seen (r = -0.482 and -0.445, respectively) when using an exponential relationship. The overall best correlation was seen against an exponential function of the OSI (r = 0.600). Although these correlation coefficients were not high, they were found to be statistically significant as evidenced by the large F-statistic obtained. Finally, it was observed that over 75 percent of the IH occurred at or below a mean WSR value of 100 s(-1) while approximately 92 percent of the IH occurred at or below a mean WSR equal to one-half that of the native artery. Therefore, while not being the only factor involved, wall shear (and in particular, oscillators wall shear) appears to provide a stimulus for the development of anastomotic intimal hyperplasia.

Anastomosis, Surgical↗

PubMed1999

The effect of graft caliber upon wall shear within in vivo distal vascular anastomoses.

Wall shear has been widely implicated as a contributing factor in the development of intimal hyperplasia in the anastomoses of chronic arterial bypass grafts. Earlier studies have been restricted to either: (1) in vitro or computer simulation models detailing the complex hemodynamics within an anastomosis without corresponding biological responses, or (2) in vivo models that document biological effects with only approximate wall shear information. Recently, a specially designed pulse ultrasonic Doppler wall shear rate (PUDWSR) measuring device has made it possible to obtain three near-wall velocity measurements nonintrusively within 1.05 mm of the vessel luminal surface from which wall shear rates (WSRs) were derived. It was the purpose of this study to evaluate the effect of graft caliber, a surgically controllable variable, upon local hemodynamics, which, in turn, play an important role in the eventual development of anastomotic hyperplasia. Tapered (4-7 mm I.D.) 6-cm-long grafts were implanted bilaterally in an end-to-side fashion with 30 deg proximal and distal anastomoses to bypass occluded common carotid arteries of 16 canines. The bypass grafts were randomly paired in contralateral vessels and placed such that the graft-to-artery diameter ratio, DR, at the distal anastomosis was either 1.0 or 1.5. For all grafts, the average Re was 432 +/- 112 and the average Womersley parameter, alpha, was 3.59 +/- 0.39 based on artery diameter. There was a sharp skewing of flow toward the artery floor with the development of a stagnation point whose position varied with time (up to two artery diameters) and DR (generally more downstream for DR = 1.0). Mean WSRs along the artery floor for DR = 1.0 and 1.5 were found to range sharply from moderate to high retrograde values (589 s-1 and 1558 s-1, respectively) upstream to high antegrade values (2704 s-1 and 2302 s-1, respectively) immediately downstream of the stagnation point. Although there were no overall differences in mean and peak WSRs between groups, there were significant differences (p < 0.05) in oscillatory WSRs as well as in the absolute normalized mean and peak WSRs between groups. There were also significant differences (p < 0.05) in mean and peak WSRs with respect to axial position along the artery floor for both DR cases. In conclusion, WSR varies widely (1558 s-1 retrograde to 2704 s-1 antegrade) within end-to-side distal graft anastomoses, particularly along the artery floor, and may play a role in the development of intimal hyperplasia through local alteration of mass transport and mechano-signal transduction within the endothelium.

Analysis of Variance↗

PubMed1998

In vitro evaluation of electrostatic endothelial cell transplantation onto 4 mm interior diameter expanded polytetrafluoroethylene grafts.

PURPOSE: To perform an in vitro evaluation of electrostatic endothelial cell transplantation of human umbilical vein endothelial cells (HUVEC) onto segments of 4 mm internal diameter expanded polytetrafluoroethylene (ePTFE) vascular prostheses. METHODS: This evaluation consisted of exposing vascular graft segments that had been subjected to either electrostatic or gravitation transplantation with HUVEC to a physiologic shear stress (15 dynes/cm2) under steady flow conditions within a flow loop system. Biochemical assays were performed on freshly transplanted grafts by means of radioimmunoassay for prostacyclin and thromboxane A2. RESULTS: There was a 30% loss of HUVEC after 30 minutes of shear stress exposure from the grafts subjected to gravitational transplantation with no additional significant (alpha = 0.05) loss after 120 minutes. Grafts subjected to electrostatic transplantation had no significant (alpha = 0.05) loss of HUVEC during exposure to physiologic shear stress. Furthermore, after 120 minutes of shear-stress exposure, the grafts subjected to electrostatic transplantation (78,420 +/- 6274 HUVEC/cm2) retained 2.3 times more HUVEC than the counterparts subjected to gravitational transplantation (34,427 +/- 4637 HUVEC/cm2). The biochemical assay results indicated no significant (alpha = 0.05) production of prostacyclin or thromboxane A2 regardless of the method of cell transplantation. CONCLUSIONS: (1) The electrostatic transplantation technique was superior to the gravitational transplantation technique in terms of cellular retention when the ePTFE grafts were exposed to physiologic shear stress. (2) Production of prostacyclin and thromboxane A2 did not differ between transplanted HUVEC subjected to gravitational or electrostatic procedures.

Blood Vessel Prosthesis↗

PubMed1994

The effect of angle and flow rate upon hemodynamics in distal vascular graft anastomoses: a numerical model study.

Flow in distal end-to-side anastomoses of iliofemoral artery bypass grafts was simulated using a steady flow, three-dimensional numerical model. With the proximal artery occluded, anastomotic angles were varied over 20, 30, 40, 45, 50, 60 and 70 deg while the inlet Reynolds numbers were 100 and 205. Fully developed flow in the graft became somewhat skewed toward the inner wall with increasing angle for both Reynolds numbers. Separated flow regions were seen along the inner arterial wall (toe region) for angles > or = 60 deg at Re = 100 and for angles > or = 45 deg at Re = 205 while a stagnation point existed along the outer arterial wall (floor region) for all cases which moved downstream relative to the toe of the anastomosis with decreasing angles. Normalized shear rates (NSR) along the arterial wall varied widely throughout the anastomotic region with negative values seen in the separation zones and upstream of the stagnation points which increased in magnitude with angle. The NSR increased with distance downstream of the stagnation point and with magnitudes which increased with the angle. Compared with observations from chronic in vivo studies, these results appear to support the hypothesis of greater intimal hyperplasia occurring in regions of low fluid shear.

Anastomosis, Surgical↗

PubMed1994

Derivation of shear rates from near-wall LDA measurements under steady and pulsatile flow conditions.

Atherosclerosis, thrombosis, and intimal hyperplasia are major forms of cardiovascular diseases in the United States. Previous studies indicate a significant correlation between hemodynamics, in particular, wall shear rate, and pathology of the arterial walls. While results of these studies implicate morphologic and functional changes related to wall shear rate magnitude, a standard technique for wall shear rate measurement has not been established. In this study, theoretical and in-vitro experimental fully developed steady and physiologic pulsatile flow waveforms have been used to obtain velocity profiles in the near-wall region. The estimated wall shear rates from these results are compared to the theoretical value to assess the accuracy of the approximating technique. Experimentally obtained results from LDA suggest that in order to minimize the error in velocity data, and subsequently, the wall shear rate, the first measured velocity has to be 500 microns away from the wall. While a linear approximation did not produce errors larger than 16.4 percent at peak systole, these errors substantially increased as the velocity magnitudes decreased during late systole and diastole. Overall, a third degree polynomial curve fit using four points produced the most accurate estimation of wall shear rate through out the cardiac cycle. Results of higher degree curve-fitting functions can be unpredictable due to potential oscillations of the function near the wall. Hence, based on the results of this study, use of a linear approximation is not recommended; a third degree curve-fitting polynomial, using four points provided the most accurate approximation for these flow waveforms.

Bias↗

PubMed1994

Effect of controlled local acetylsalicylic acid release on in vitro platelet adhesion to vascular grafts.

Thrombosis is the most serious acute problem for small diameter arterial bypass grafts. In this research, small diameter expanded polytetrafluoroethylene (e-PTFE) vascular grafts were coated with acetylsalicylic acid (ASA) loaded poly (d,l-lactide) (PLA) by a solvent casting method. The feasibility and efficacy of this approach were evaluated by ASA release studies and platelet adhesion tests. First, the ASA release kinetics were evaluated from the ASA/PLA coated vascular grafts in an in vitro steady flow loop model. ASA release was measured by a spectrophotometric technique. Finally, the efficacy of local ASA release to reduce in vitro canine platelet adhesion to grafts was determined with epifluorescent video microscopy and quantitative image analysis. The steady state release rates from the 5%, 10%, and 15% ASA/PLA coated grafts were 13.2 x 10(-5), 32.0 x 10(-5), and 41.5 x 10(-5) micrograms/cm2.sec, respectively. Platelet adhesion to 10% and 15% ASA/PLA coated grafts was reduced with respect to the control and 5% grafts for 10 days. Platelet adhesion to 5% ASA/PLA coated grafts was reduced with respect to controls at 2 and 10 days, but not initially.

Animals↗

PubMed1993

Doppler color flow images of iliofemoral graft end-to-side distal anastomotic models.

Hemodynamics within the distal anastomoses of iliofemoral bypass grafts were simulated using Plexiglas models (2.5 cm ID) within a pulsatile flow loop system (Re(mean) = 92, Re(peak) = 459 and alpha = 3.56). End-to-side distal anastomoses were constructed with angles of 30 degrees, 45 degrees and 60 degrees to bypass proximal artery segments with stenoses of 60% and 100% diameter reduction. Velocities were obtained over a two-dimensional field within the artery using an ultrasonic Doppler color flow imager operating at 5 MHz at positions from 1.5 diameters upstream to 3 diameters downstream of the anastomosis. Flow patterns downstream of an occlusion demonstrated definite skewing effects toward the outer wall with resultant flow separation along the inner wall. Presence of a partial (60% diameter reduction) arterial stenosis upstream of the anastomosis produced flow separation along both artery walls and a more symmetric profile downstream. Measurement of a separation area index (SAI) along each arterial wall demonstrated a minimum area exposed to low velocities for the 30 degrees anastomotic angle compared to the 45 degrees and 60 degrees anastomotic angles and for the occluded proximal artery cases compared to corresponding stenotic artery cases. The SAI values were minimal at peak systole compared to successive quarter cycle intervals. The findings of this study provide further information regarding the relationship between local fluid mechanics and predominant sites for intimal hyperplasia formation.

Anastomosis, Surgical↗

PubMed1992

Quantification of Doppler color flow images from a stenosed carotid artery model.

Velocity fields at and downstream of graded, axisymmetric stenoses of 0%, 20%, 40%, 60% and 80% diameter reduction were obtained under pulsatile flow conditions simulating that in a carotid artery (Re(mean) = 379, Re(peak) = 1137 and alpha = 5.36) using an ultrasonic Doppler Color Flow Imager. Characteristic features of flow disturbances associated with degree of stenosis, such as jetting, flow separation and reversal and turbulence were quantified using nondimensional indices at peak systole, t0, and early diastole, t1. It was found that the Reverse Area Index (RAI), the Field Profile Index (FPI) and the Velocity Gradient Indices (VGIz and VGIr) were sensitive to these changes, especially at time t1. In particular, the mean values of RAI and VGIr were significantly different for all stenotic cases. These findings may provide a more quantitative and reproducible method of interpreting flow patterns in the region of stenosed carotid arteries.

Blood Flow Velocity↗

PubMed1991

The effect of angle and flow rate upon hemodynamics in distal vascular graft anastomoses: an in vitro model study.

A steady flow, in vitro model of distal arterial bypass graft junctions was used to examine the effects of junction angle and flow rate on the local velocity field. Three test sections were fabricated from Plexiglas tubing having anastomotic junction angles of either 30, 45, or 60 deg. Flow visualization revealed velocity profiles skewed toward the outer wall with a flow split around a clear stagnation point along the outer wall. Laser Doppler anemometry [LDA] measurements confirmed a distinct stagnation point at the outer wall and both reverse and forward shear were detected immediately upstream and downstream, respectively, of this site. Axial velocities and shear rates along the outer wall were higher than along the inner wall and occurred in the junction angle order: 45, 60, and 30 deg. This study clearly identified changes in wall shear which varied with the anastomotic angle and flow rate.

Anastomosis, Surgical↗

PubMed1990

Doppler color-flow images from a stenosed arterial model: interpretation of flow patterns.

The capability of the recently introduced Doppler color-flow mapping devices to accurately detect flow patterns in the region of an arterial stenosis was evaluated by use of an in vitro flow model. Pulsatile flow simulating that in a low-resistance vessel was induced through a straight acrylic tube, which alternatively contained axisymmetric stenoses of 0%, 20%, 40%, 60%, and 80% diameter reduction. Doppler color-flow mapper images were taken in realtime along the tube midplane from 0 to 8 diameters downstream of each stenosis. Comparison of the Doppler color-flow mapping results with similarly recorded flow visualization (hydrogen bubble) images showed a close correspondence of key features of the flow, including detection of a high-velocity, centerline jet and near-wall separated flow zones. Distinctive flow patterns exist with each stenotic case, and these should be of considerable value in diagnosing clinical disease conditions.

Arterial Occlusive Diseases↗

PubMed1990

Velocity profiles in stenosed models using magnetic resonance imaging.

A time-of-flight MRI velocity measurement technique is evaluated against corresponding LDV measurements in a constriction tube model over a range of physiologic flow conditions. Results from this study show that MR displacement images can: (1) be obtained within both laminar and turbulent jets (maximum stenotic Re approximately equal to 4,200); (2) measure mean jet velocities up to 172 cm/s, and (3) detect low forward and reverse velocity regions near the tube wall just downstream of the stenosis (0 less than or equal to L/D less than or equal to 2). Regions between the jet termination point and reestablishment of laminar flow (Re greater than 1,500, greater than 1,000 and greater than 110 downstream of 40, 60 and 80% stenosis, respectively) cannot presently be detected by this technique.

Blood Flow Velocity↗

PubMed1988

Flow dynamics in a stenosed carotid bifurcation model--Part I: Basic velocity measurements.

A model of the human carotid artery bifurcation has been constructed and tested under mean physiologic flow conditions (fluid viscosity = 0.035 poise; mean Re inlet = 400; unconstricted flow split = 70:30, internal carotid artery:external carotid artery). Smooth, axisymmetric constrictor plugs with 0, 20, 40, 60, and 80% diameter reduction are placed in the simulated proximal internal carotid artery to provide a range of flow conditions similar to those found clinically. Axial velocity measurements are made at sites +/- 0.625 radius within the lumen of the tube at distances of 0, 1, 3, 5 and 10 diameters downstream of the constrictor throat using H2 bubble markers and a 7.5 MHz ultrasound pulse Doppler. Measurement of mean, mode -3 dB down high and low and -9 dB down high and low velocities are made from selected fast-Fourier transform (FFT) spectra. The flow field downstream of the 0% diameter reduction is entirely laminar, exhibiting a peak skewed toward the flow divider along the entire 10 diameters downstream and having a consistently narrow bandwidth. Obstruction of the flow channel produces increased axial velocity at the constrictor (20%), an oscillatory jet extending approximately 5 diameters downstream (40%), a transitional jet extending approximately 5 diameters downstream (60%) and a turbulent jet extending approximately 3 diameters downstream (80%). Velocity bandwidth (both -3 dB and -9 dB) increases with degree of constriction and low velocity flow patterns exist between the center line and both tube walls. Presence of constriction produces characteristic downstream flow patterns which are distinctive for each degree of diameter reduction.

Blood Flow Velocity↗

PubMed1988

Flow dynamics in a stenosed carotid bifurcation model--Part II: Derived indices.

Basic velocity measurements from the previous study in this issue of modelled carotid artery bifurcation disease are post-processed to derive indices potentially useful for clinical diagnosis. Selected parameters are based upon ultrasound pulse Doppler velocity measurements made at sites +/- 0.625 radius at axial distances of 0, 1, 3, 5, and 10 diameters downstream of smooth, axially symmetric constrictions of 0, 20, 40, 60, and 80% diameter reduction. Indices based on single point velocity measurements include: (a) the center-line velocity index (CVI) at the throat of the constrictor which is sensitive to all degrees of constriction (p less than 0.05), and (b) various measures of velocity disturbance (VDI1-VD14) which show greatest sensitivity when measured at one-fourth diameter from the tube wall. Cross-sectional indices include: (a) the maximum slope index (MSI) which separates constrictions of less than 60% diameter reduction from those having greater than or equal to 60% diameter reduction (p less than 0.05), and (b) the cross-sectional profile index (CPI) which separates constrictions of less than or equal to 20% diameter reduction from those having greater than 20% diameter reduction (p less than 0.05). A field profile index (FPI) utilizes data from all available sites up to 5 diameters downstream and is able to separate all constrictor groups (p less than 0.05). Presence of constrictions produces characteristic flow patterns which can be quantified using indices based on the downstream velocity spectra. Specifically, locally increased velocity is very sensitive to degree of constriction and is best detected along the center line. Disturbance effects, while less pronounced, are complementary to changes in velocity magnitude and are first seen off-axis. Multiple point profile measures (cross sectional and full field) are also sensitive to degree of constriction and are best evaluated at 1 diameter and over 5 diameters, respectively, downstream of the constriction. All of the nondimensional indices offer the advantages of reduced probe and angle dependence and particular approaches may be implemented according to the data collection capability of the instrument used.

Blood Flow Velocity↗

PubMed1988

Velocity profiles in stenosed tube models using magnetic resonance imaging.

A time-of-flight MRI velocity measurement technique is evaluated against corresponding LDV measurements in a constriction tube model over a range of physiologic flow conditions. Results from this study show that MR displacement images can: 1) be obtained within both laminar and turbulent jets (maximum stenotic Re approximately equal to 4,200), 2) measure mean jet velocities up to 172 cm/s, and, 3) detect low forward and reverse stenosis (0 less than or equal to L/D less than or equal to 2). Regions between the jet termination point and re-establishment of laminar flow (Re greater than or equal to 1500, greater than or equal to 1000, and greater than or equal to 110 downstream of 40, 60, and 80 percent stenosis, respectively) cannot presently be detected by this technique.

Blood Flow Velocity↗

PubMed1986

Noninvasive blood flow measurement in expanded polytetrafluoroethylene grafts for hemodialysis access.

Volume flow rates were measured in 31 expanded polytetrafluoroethylene grafts (6 mm) of 26 patients undergoing hemodialysis. Flow was calculated from the known access graft diameter and by measurement of the mean Doppler shift frequency waveform. Overall flow rates were 750 +/- 383 ml/min (range, 0 to 1921 ml/min). There was no difference in flow between grafts anastomosed to either antecubital or upper arm veins but there was a significant difference in flow rate between straight and loop grafts (652 and 914 ml/min) and between grafts anastomosed to the radial, distal brachial, and proximal brachial arteries (648, 876, and 1169 ml/min, respectively). Flow rates measured during a preocclusive 14-day period in five grafts were significantly lower than flow rates in grafts that remained patent for at least 2 weeks following examination (307 +/- 172 vs. 849 +/- 346 ml/min). This is a safe, repeatable noninvasive measure of access graft hemodynamics, which may be useful as a functional monitor and a warning of impending failure.

Arteriovenous Shunt, Surgical↗

PubMed1984

Noninvasive evaluation of renal artery stenosis and renovascular resistance. Experimental and clinical studies.

Doppler ultrasound was used to detect experimental and clinical renal artery stenosis (RAS) and increased renovascular resistance (RVR). Parameters assessing RAS included elevated systolic frequency and spectral broadening, while diastolic/systolic frequency ratios predicted elevated RVR. In canine models these parameters detected graded RAS before reduction in renal blood flow. Index values were 88% sensitive and 100% specific in identifying RAS with gradients greater than or equal to 25 mm Hg. Diastolic/systolic frequency correlated well with increased RVR induced by microsphere injections (p less than 0.05). Duplex scanning noninvasively detected bilateral renal artery velocity in 113 of 120 patients. Index values were 83% sensitive and 97% specific in identifying greater than or equal to 60% RAS in 86 vessels visualized by angiography. Estimated RVR was significantly higher in age-matched hypertensive and atherosclerotic patients than in controls (p less than 0.01). Ultrasound may be useful to screen patients for RAS and increased RVR.

Adult↗