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At least 289 records · Page 16Linked to original sources

PubMed2001

Blood flow in abdominal aortic aneurysms: pulsatile flow hemodynamics.

Numerical predictions of blood flow patterns and hemodynamic stresses in Abdominal Aortic Aneurysms (AAAs) are performed in a two-aneurysm, axisymmetric, rigid wall model using the spectral element method. Physiologically realistic aortic blood flow is simulated under pulsatile conditions for the range of time-averaged Reynolds numbers 50< or =Re(m)< or =300, corresponding to a range of peak Reynolds numbers 262.5< or =Re(peak) < or = 1575. The vortex dynamics induced by pulsatile flow in AAAs is characterized by a sequence of five different flow phases in one period of the flow cycle. Hemodynamic disturbance is evaluated for a modified set of indicator functions, which include wall pressure (p(w)), wall shear stress (tau(w)), and Wall Shear Stress Gradient (WSSG). At peak flow, the highest shear stress and WSSG levels are obtained downstream of both aneurysms, in a pattern similar to that of steady flow. Maximum values of wall shear stresses and wall shear stress gradients obtained at peak flow are evaluated as a function of the time-average Reynolds number resulting in a fourth order polynomial correlation. A comparison between predictions for steady and pulsatile flow is presented, illustrating the importance of considering time-dependent flow for the evaluation of hemodynamic indicators.

Aortic Aneurysm, Abdominal↗

PubMed2005

PIV measurements of flow in a centrifugal blood pump: time-varying flow.

Measurements of the time-varying flow in a centrifugal blood pump operating as a left ventricular assist device (LVAD) are presented. This includes changes in both the pump flow rate as a function of the left ventricle contraction and the interaction of the rotating impeller and fixed exit volute. When operating with a pulsing ventricle, the flow rate through the LVAD varies from 0-11 L/min during each cycle of the heartbeat. Phase-averaged measurements of mean velocity and some turbulence statistics within several regions of the pump, including the inlet, blade passage, exit volute, and diffuser, are reported at 20 phases of the cardiac cycle. The transient flow fields are compared to the constant flow rate condition that was reported previously in order to investigate the transient effects within the pump. It is shown that the quasi-steady assumption is a fair treatment of the time varying flow field in all regions of this representative pump, which greatly simplifies the comprehension and modeling of this flow field. The measurements are further interpreted to identify the effects that the transient nature of the flow field will have on blood damage. Although regions of recirculation and stagnant flow exist at some phases of the cardiac cycle, there is no location where flow is stagnant during the entire heartbeat.

Algorithms↗

PubMed1994

Estimation of total coronary artery flow using measurements of flow in the ascending aorta.

This paper describes a technique for estimation of total (right+left) coronary artery flow using MRI flow measurements in the ascending aorta. The technique is based on the principle that the flow in a vessel branch is equal to the difference of the net flow measured above and below the branch ostia. Aortic net flow is measured at four or more axial oblique slices from below the aortic valve to above the highest location of the coronary vessel ostia in late diastole. A flow model properly interprets the flow measurements in slices that contain the coronary ostia. Results in five normal subjects show that total coronary artery flow can be measured with a standard error of about 90 cc/min, 30% of total coronary artery flow. Potential clinical uses include noninvasive measurement of coronary flow reserve. Pulse sequence improvements are necessary to reduce examination time and improve accuracy and precision.

Algorithms↗

PubMed1997

Coronary flow and coronary flow reserve measurements in humans with breath-held magnetic resonance phase contrast velocity mapping.

Objective evidence for coronary lesion significance can be obtained with ischemic stress testing. Since flow-limiting stenoses have already undergone compensatory vasodilatation to maintain flow, the response to vasoactive stimulation is dampened. The degree of response limitation is reflected by the coronary flow reserve (CFR). Absolute volume flow rates can be accurately and noninvasively measured with MRI techniques. The purpose was to assess the ability to measure coronary volume flow rate noninvasively, and characterize the effect of pharmacologic stress on coronary flow quantitatively by using ultrafast, breath-held segmented k-space phase-contrast-MR imaging (PC-MRI). Ten healthy volunteers were examined by using ultrafast breath-held PC-MRI. Coronary volume flow rates were measured in the anterior descending coronary artery (LAD) at rest and following intravenous administration of dipyridamole. CFR was determined based on these data. Mean LAD volume flow rates increased from 38 +/- 11 ml/min before application of dipyridamole to 169 +/- 42 ml/min. The mean CFR amounted to 5.0 +/- 2.6 (median = 4.15). This study demonstrates the feasibility of breath-held PC-MRI to noninvasively quantify coronary volume flow rates over the cardiac cycle. Pharmacologically induced changes in volume flow rate and thus CFR can be quantitated.

Adult↗

PubMed1995

The effect of partial portal decompression on portal blood flow and effective hepatic blood flow in man: a prospective study.

With the advent of transjugular intrahepatic porta-systemic stent shunt and the wider application of the surgically placed small diameter prosthetic H-graft portacaval shunt (HGPCS), partial portal decompression in the treatment of portal hypertension has received increased attention. The clinical results supporting the use of partial portal decompression are its low incidence of variceal rehemorrhage due to decreased portal pressures and its low rate of hepatic failure, possibly due to maintenance of blood flow to the liver. Surprisingly, nothing is known about changes in portal hemodynamics and effective hepatic blood flow following partial portal decompression. To prospectively evaluate changes in portal hemodynamics and effective hepatic blood flow brought about by partial portal decompression, the following were determined in seven patients undergoing HGPCS: intraoperative pre- and postshunt portal vein pressures and portal vein-inferior vena cava pressure gradients, intraoperative pre- and postshunt portal vein flow, and pre- and postoperative effective hepatic blood flow. With HGPCS, portal vein pressures and portal vein-inferior vena cava pressure gradients decreased significantly, although portal pressures remained above normal. In contrast to the significant decreases in portal pressures, portal vein blood flow and effective hepatic blood flow do not decrease significantly. Changes in portal vein pressures and portal vein-inferior vena cava pressure gradients are great when compared to changes in portal vein flow and effective hepatic blood flow. Reduction of portal hypertension with concomitant maintenance of hepatic blood flow may explain why hepatic dysfunction is avoided following partial portal decompression.

Blood Pressure↗

PubMed1988

Effects of vasospasm in the middle cerebral artery territory on flow velocity and volume flow. A computersimulation.

Recently blood flow velocity in large cerebral arteries became measurable non-invasively by transcranial Doppler sonography (TCD). The present study tries to quantify the relation between flow velocity and the more important volume flow in the middle cerebral artery (MCA) by means of computersimulation. A mathematical model of the MCA territory was developed. The model is able to take into account the non-Newtonian behaviour of blood viscosity and is also able to handle turbulant and laminar flow. Autoregulation is simulated by increasing or decreasing diameter of arteries as an answer to intraluminal pressure changes. Two processes are simulated: Vasospasm in the stem of the MCA, and vasospasm in the entire MCA territory. Results show that the relation between flow velocity and volume flow is rather complicated. Vasospasm in the MCA stem first leads to an increase of flow velocity at a constant level of volume flow. At higher grades of vessel constriction volume flow and flow velocity start to fall.

Animals↗

PubMed1986

Pulsatile flow simulator for comparison of cardiac output measurements by electromagnetic flow meter and thermodilution.

This study examined a pulsatile flow simulator for the purpose of evaluating two measurement devices, an extracorporeal flow probe with an electromagnetic flow meter and several thermodilution catheters. We measured the performance of these devices in a range of low to high flows. Using either saline or blood as a perfusate, we obtained different results with these fluids (p less than 0.001). Each catheter behaved in a linear manner, although variation occurred among the catheters with both saline (minimum slope 1.090, maximum slope 1.190) and blood (minimum slope 1.107, maximum slope 1.154). An increase in rate and stroke volumes of the simulator did not demonstrate an identifiable trend in error. The thermodilution catheters were most accurate at 5.0 L/min irrespective of rate, stroke volume, or perfusate used. In contrast, the electromagnetic flow meter accurately represented flows across the wide range of outputs examined (2.4 to 10.7 L/min). (Slope with saline 1.091, slope with blood 1.080) Throughout the range of flow, the flow meter gave a calibration line 5% higher with blood than with saline. The results indicate that accurate measurement of pulsatile blood flow can be achieved in vitro with an electromagnetic flow meter using saline as a perfusate, provided a correction factor is determined and applied to convert values for saline to accurate values for blood.

Blood Flow Velocity↗

PubMed1987

Basic flow structure in saccular aneurysms: a flow visualization study.

Basic flow patterns were investigated in a set of glass aneurysm models by means of flow visualization methods. Dye injection and streaming double refraction were used to visualize flow. The circulation inside lateral aneurysms arising at a 90 degree angle from a straight parent conduit could not be visualized by the dye-injection technique but could be demonstrated by streaming double refraction. The inflow was seen to arise from the downstream lip of the orifice and to project to the dome of the aneurysm. Backflow to the parent conduit took place along the walls of the aneurysm. In aneurysms located at bifurcations, flow characteristics depended on the geometry of the bifurcation and the flow ratio between the branches. Relatively little intra-aneurysmal flow was demonstrated in side branch-related aneurysms arising distal to an asymmetric 90 degrees bifurcation of the type encountered at the junction of the internal carotid and posterior communicating arteries. Stagnation of flow at the neck and little intra-aneurysmal circulation were found with terminal aneurysms of the basilar bifurcation type if the outflow through the branches was symmetric. With asymmetric outflow, however, or if the axis of the aneurysm did not coincide with that of the afferent vessel, an active rotation developed in these aneurysms. The size of the aneurysm had no influence on the basic pattern of intra-aneurysmal circulation. The use of pulsatile perfusion did not significantly alter the basic flow patterns observed with steady flow. Locally disturbed laminar flow was observed in certain models at physiological Reynold's numbers, but there were no signs of fully developed turbulence.

Coloring Agents↗

PubMed1997

The sensitivity of new color systems in blood-flow diagnosis. The maximum entropy method and angio-color-comparative in vitro flow measurements to determine sensitivity.

BACKGROUND: Two new blood-flow-diagnosis techniques have recently been developed as supplements to the established color techniques: the MEM (maximum entropy method) technique and color flow amplitude (power Doppler). These are capable of representing blood flow in distinctly more slowly flowing areas than is possible with the conventional Doppler technique. METHODS: Both methods make use of the Doppler technique in part, yet analyze the reflected signal in a different manner, in so doing optimizing the relation between the noise and the signal. Measurements were obtained on two anatomic flow models to test the sensitivity of both techniques under slow flow conditions. RESULTS: The slowest flow the MEM technique was capable of recording was 0.5 mm/s, albeit utilizing a 5-MHz transducer for the MEM technique and a 10-MHz transducer for the angio technique. One may thus assume that the MEM technique would be still more sensitive when utilizing a 10-MHz transducer. The advantage of the MEM technique is its real-time flow representation: The angio technique requires a few seconds of acquisition time. This could have serious consequences during clinical utilization. Doppler sonography was merely capable of detecting a minimum flow velocity of 15 mm/s. The angio technique is less dependent on the angle during flow representation than the MEM technique. CONCLUSIONS: The distinctly higher sensitivity of these two new color techniques offers new possibilities in the clinical sector as far as the perfusion diagnosis of organs and tumors is concerned.

Angiography↗

PubMed1994

Effects of heart rate on phasic coronary blood flow pattern and flow reserve in patients with normal coronary arteries: a study with an intravascular Doppler catheter and spectral analysis.

To assess the effects of pacing-induced tachycardia on phasic coronary blood flow pattern and flow reserve of left anterior descending artery, we examined 16 patients with chest pain and angiographically normal coronary arteries by using an intravascular Doppler catheter with spectral analysis of the velocity signal. The heart rate was increased from a mean of 68 +/- 11 beats/min during sinus rhythm to 100 beats/min and again to 120 beats/min. Cross-sectional area of the epicardial artery and resting systolic and diastolic coronary blood flows increased progressively, resulting in an elevation of total coronary flow from 142 +/- 54 ml/min during sinus rhythm to 190 +/- 66 ml/min at 100 beats/min (p < 0.05) and to 219 +/- 69 ml/min at 120 beats/min (p < 0.01). During maximal hyperemia with intracoronary injection of 10 to 12 mg of papaverine, there was an increase in the systolic coronary blood flow with a decrease in the diastolic flow, resulting in no significant change in the total flow. These alterations led to progressive reductions in coronary flow reserve from 3.9 +/- 0.7 during sinus rhythm to 2.9 +/- 0.9 at 100 beats/min (p < 0.01) and to 2.3 +/- 0.3 at 120 beats/min (p < 0.001). Thus careful consideration should be given to the effects of heart rate when phasic coronary blood flow pattern and flow reserve are assessed.

Adult↗

PubMed1993

Spectral analysis of flow velocity in the contralateral artery during coronary angioplasty: a new method for assessing collateral flow.

OBJECTIVES: The present study was designed to evaluate a new method for assessing coronary collateral flow and resistance in conscious humans. BACKGROUND: Earlier pathomorphologic and invasive studies have indicated that collateral vessels are important for salvage of myocardium at risk in acute myocardial infarction. Only a few clinical studies have attempted to express the development of the collateral vascular bed in terms of flow or resistance. METHODS: Angiography and flow velocity measurements of the contralateral coronary artery were performed in 38 patients undergoing coronary angioplasty for one-vessel disease. Coronary flow velocity was assessed by zero-crossing frequency analysis in 37 patients and, additionally, by fast Fourier transform spectral analysis in 23. Collateral flow was determined by the decrease of flow velocity after balloon deflation. Mean aortic pressure and coronary wedge pressure were assessed for calculation of collateral vascular resistance. RESULTS: Angiography of the contralateral artery during balloon inflation revealed the presence of collateral vessels in 26 patients (recruitable collateral vessels in 19). Fast Fourier transform spectral analysis demonstrated a significant transient increase of flow velocity during brief coronary occlusion in 15 patients with collateral vessels compared with 8 patients without collateral vessels (4.8 +/- 1.3% vs. 23.4 +/- 17.2%, p < 0.001). A transient increase in flow velocity (> 10%) was less evident by zero-crossing frequency analysis than by fast Fourier transform spectral analysis (sensitivity 8% vs. 87%). The relative resistance of the collateral vascular bed was significantly reduced when collateral vessels were present during coronary occlusion (4.4 +/- 3.8 vs. 16.9 +/- 4.6, p < 0.001). Furthermore, electrocardiographic signs of ischemia were less present in those 15 patients with collateral vessels (p < 0.05). CONCLUSIONS: The beneficial effect of collateral vessels during brief coronary occlusion is exerted by a significant increase of flow in the contralateral artery in combination with a reduced resistance in the collateral vascular bed. The method presented is capable of expressing the development of the collateral vascular bed in terms of flow and resistance.

Adult↗

PubMed2006

Flow index evaluation of 3-D volume flow images: an in vivo and in vitro study.

Three-dimensional (3-D) ultrasound imaging has improved evaluation of organ circulation and might contribute new information on maternal and fetal blood supply. Flow index (FI) of 3-D color images has been proposed as a measure of perfusion. The aim of this study was to evaluate whether the 3-D FI is a parameter of volume flow and flow velocity in a human vessel and in a flow phantom. A 1-cm-long strip of the uterine artery was recorded in 3-D power Doppler (3D-PD) mode in a cross-sectional study of 170 normal singleton pregnancies between 26 and 42 weeks' gestation. A fixed ultrasound system installation was used during the examination. The VOCAL software integrated in the ultrasound unit calculated vessel volume and FI. Reproducibility of the measurements was tested. The method was also tested on a commercially available flow phantom. Reproducibility measurements gave satisfactory results, both in terms of inter- and intraobserver variation. Unexpectedly, in normal pregnancy, the uterine artery FI decreased slightly with gestation. Uterine artery vessel volume increased, however, with gestational age. A poor correlation was found between the FI and both flow velocity and volume flow in the flow phantom. In conclusion, 3D-PD imaging can give impressive anatomical pictures of organ vascular tree. However, the new FI is poorly related to flow velocity or volume of flow.

Arteries↗

PubMed2002

On the design of a capillary flow phantom for the evaluation of ultrasound contrast agents at very low flow velocities.

Recently, a new imaging technology has become available that allows the evaluation of tissue perfusion using echo-contrast agents in real-time imaging: power pulse inversion imaging (PPI). Although numerous in vitro phantoms have been designed for different imaging modalities in ultrasound (US), there is a need for a phantom that mimics microcirculation and allows, in particular, the assessment of contrast replenishment kinetics following US-induced destruction of microbubbles using the new method. We, therefore, designed a new capillary flow phantom that takes the requirements of the new US imaging techniques and the physical properties of microbubbles into account and serves flow velocities in the range of microcirculation (1 to 10 mm/s). PPI studies were performed in the newly designed phantom. The contrast agent used was AF0150. We studied homogeneity of contrast distribution within the capillary phantom, constancy of contrast infusion, the dose-effect relationship and, finally, the feasibility of flow assessment using the method of contrast replenishment following US-induced microbubble destruction in a flow velocity range of 2.1 to 9.45 mm/s. Analysis of the replenishment kinetics was performed using the mathematical model f(t) = A(1 - e(-beta t)), with A representing the blood volume and beta the microbubble velocity. The new capillary phantom allowed homogeneous contrast opacification within the perfused capillaries independently of the flow. Constancy of signal intensity was achieved over a time period of almost 2 h, indicating constant contrast delivery. A strong linear correlation between the PPI signal and the contrast dose was found (r = 0.998). Analysis of the replenishment parameters revealed a strong linear relationship between parameter beta and flow (r = 0.994) as well as A * beta and flow (r = 0.984) in the observed flow range. The newly designed perfusion phantom for the evaluation of echo-contrast replenishment kinetics fulfills, at very low flow velocities, important prerequisites such as constancy of contrast delivery, homogeneity of contrast signals, linear dose-effect relation and minimal attenuation. Thus, the new phantom allows standardized analysis of contrast replenishment kinetics using real-time perfusion imaging techniques at flow velocities comparable to those of the microcirculation.

Blood Flow Velocity↗

PubMed1998

Evaluation of coronary flow velocity dynamics and flow reserve in patients with Kawasaki disease by means of a Doppler guide wire.

OBJECTIVES: To assess the pathophysiologic effects of the coronary sequelae of Kawasaki disease on coronary hemodynamic variables, we regionally evaluated the flow velocity dynamics and flow reserve in coronary vessels with lesions using an intracoronary Doppler flow guide wire. BACKGROUND: The pathophysiologic effects of the coronary sequelae of Kawasaki disease on coronary hemodynamic variables have not been completely clarified, and we previously reported some discrepancies between coronary angiographic findings and exercise stress tests in Kawasaki disease. METHODS: Doppler phasic coronary flow velocity was determined using an 0.018-in. (0.046-cm) intracoronary Doppler flow guide wire at rest and during the adenosine triphosphate-induced hyperemic response in 95 patients (75 male, 20 female, mean age 9.8+/-6.2 years) with Kawasaki disease. RESULTS: In 25 patients with coronary aneurysms in 29 vessels, the average peak velocity and diastolic to systolic velocity ratio were significantly (p < 0.05) decreased in the moderate-sized and large-sized aneurysms. Significantly lower values in coronary flow reserve (CFR) were noted in 3 of 10 vessels with moderate aneurysms and in 4 of 7 vessels with large aneurysms. A significant positive correlation (y = 0.53x + 14.6, r2 = 0.91) was observed between the percent diameter stenosis evaluated by angiography and that calculated from the flow velocity measurement. However, the percent diameter stenosis calculated from the flow velocity measurement was underestimated compared with that determined by angiography in the stenotic lesions of intermediate severity. A reduced CFR was noted in five of seven vessels with intermediate stenosis ranging from 50% to 75%, and also in three vessels with mild stenosis ranging from 30% to 40%. A reduced CFR was also observed in six of the eight angiographically normal vessels associated with the area of reduced perfusion on exercise thallium-201 myocardial scintigraphy. CONCLUSIONS: Abnormalities in flow dynamics and a reduction in flow reserve were revealed in coronary aneurysms of intermediate to large size and in stenotic lesions, even of mild to intermediate severity, in patients with Kawasaki disease. Abnormalities in the coronary microcirculation, as well as epicardial lesions, contribute to the pathophysiologic responses in Kawasaki disease.

Adolescent↗

PubMed2003

Effects of heart rate on phasic Y-graft blood flow and flow reserve in patients with complete arterial myocardial revascularizaton: an intravascular Doppler catheter study.

OBJECTIVE: It is not well established whether the blood flow of arterial composite Y-grafts can efficiently respond to the flow demand of the coronary system early postoperatively. The aim of this study was to evaluate if soon after the operation, arterial composite Y-grafts can increase blood flow in response to an increase in myocardial oxygen consumption (MVO2). METHODS: Twenty-seven patients who received complete arterial myocardial revascularization using the left internal thoracic artery (LITA) and the radial artery (RA) as composite Y-graft gave their consent to a pre-discharge coronary angiography and intravascular flow velocity measurements using a Doppler guide wire. Flow measurements were performed in the LITA main stem, the distal LITA and the RA, both at rest and during atrial pacing at the 85% of the patient age-predicted maximum. The heart rate-systolic blood pressure product was considered as an indirect index of MVO2. Hyperemic flow was determined after injection of adenosine. The flow reserve (FR) was defined as the ratio of blood flow during maximal hyperemia (Qmax) to baseline flow (Qbasal). RESULTS: Atrial pacing increased MVO2 significantly (P<0.000). None of the patients developed ischemic S-T segment modifications or complained of chest pain. Q(basal) increased significantly in the LITA main stem (P=0.001), distal LITA (P=0.041) and RA (P=0.004) while Qmax did not change significantly. As a consequence, the FR decreased in the LITA main stem (P=0.002), distal LITA (P<0.000) and RA (P<0.000) but was not completely exhausted. CONCLUSIONS: Soon after the operation, arterial composite Y-grafts can significantly increase blood flow in response to conditions of increased MVO2, keeping normal the myocardial O2 supply-to-demand ratio.

Aged↗

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↗

PubMed2003

AVM modelling by multi-branching tube flow: large flow rates and dual solutions.

Cerebral arteriovenous malformations (AVMs) present a common yet complex clinical challenge, through 'steal' phenomena, haemorrhage risks and epilepsy effects, aspects which are little understood even for individual lesions. The main difficulty lies in understanding the detailed haemodynamics of AVMs and especially the enhanced through-flow associated with steal. Mathematically, as a basic step, the paper investigates a nonlinear inviscid model for the planar incompressible flow of fluid through a branched geometry consisting of a single feeding mother tube which splits into two or more non-aligned daughter tubes. Recurrence relations between the unknown flow profiles in the daughter tubes and the incoming rotational flow profile in the mother tube are derived, analysed, and solved in detail in order to find the total flow rate. The results show greatly enhanced through-flow arising, for a fixed value of the total downstream flow area, either from non-unique solutions to the problem or more particularly from an increase in the number of daughter tubes, or from both, depending on the distribution of pressure differences applied across the branching region and the total downstream flow area. Extensions of the basic flow model are noted, along with comparisons with recent direct numerical simulations and discussion of possible repercussions in the context of treatment and clinical observations of enhanced through-flows in AVMs.

Blood Flow Velocity↗

PubMed1989

A comparison of two methods to measure coronary flow reserve in the setting of coronary angioplasty: intracoronary blood flow velocity measurements with a Doppler catheter, and digital subtraction cineangiography.

Intracoronary blood flow velocity measurements with a Doppler balloon catheter and the radiographic assessment of myocardial perfusion with contrast media, before and after the intracoronary administration of papaverine, have previously been used to investigate regional coronary flow reserve. In the present study we applied both techniques in 21 patients to measure coronary flow reserve in the setting of coronary angioplasty. Pre-angioplasty (N = 14) and post-angioplasty (N = 19) measurements of coronary flow reserve were obtained by digital subtraction cineangiography in the myocardial region supplied by the dilated coronary artery, and with the Doppler probe in the proximal part of the dilated vessel. The reactive hyperaemia following the final balloon inflation was recorded with the Doppler balloon catheter still positioned across the stenotic lesion. Coronary stenosis geometry was quantified with the Cardiovascular Angiography Analysis System. When the epicardial stenosis was the only factor causing a reduction in coronary flow reserve, flow reserve measured with both digital subtraction cineangiography and with the Doppler probe correlated well with the cross-sectional area at the site of obstruction, r = 0.88, SEE = 0.36 and r = 0.77, SEE = 0.45 respectively. In contrast, when other factors decreasing coronary flow reserve were present (intimal dissection, left ventricular hypertrophy, previous myocardial infarction, collaterals) measurements obtained with both techniques correlated poorly with cross-sectional area (r = 0.55, SEE = 0.57, and r = 0.59, SEE = 0.50). Flow reserve measurements obtained with digital subtraction cineangiography correlated well with the measurements obtained with the Doppler probe (r = 0.85, SEE = 0.38, and r = 0.87, SEE = 0.34), although the two approaches have methodologically nothing in common and their respective regions of interest (myocardium for the radiographic technique and intracoronary lumen for the Doppler technique) are basically different. Furthermore, the reactive hyperaemia following the final balloon inflation was related to the flow reserve measured with both the angiographic technique (r = 0.85, SEE = 0.34) and the Doppler technique (r = 0.83, SEE = 0.32) using pharmacologically induced coronary vasodilation with intracoronary papaverine. This suggests that the same quantity of coronary flow reserve that can be recruited pharmacologically can be recruited by ischaemia following a transluminal occlusion.

Adult↗