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At least 325 records · Page 18Linked to original sources

PubMed1989

[Cerebral blood flow rate during cardiopulmonary bypass and optimal cerebral perfusion flow rate during separated brain perfusion--a clinical study].

There is no established theory to determine the cerebral blood flow rate (CBF) during not only the standard cardiopulmonary bypass but during the cardiopulmonary bypass with separated brain perfusion. This study was carried out to answer the following questions. (1) what is the relationship during the cardiopulmonary bypass between CBF and systemic flow rate or blood pressure?. (2) what is the optimal flow rate to the innominate artery during the separated brain perfusion? Twenty-one patients were selected for this study, who were operated under the cardiopulmonary bypass with a standard roller pump and a membrane oxygenator under moderate hypothermia (nasopharyngeal temperature of 26-28 degrees C). Systemic flow rate was maintained between 40 and 70 ml/kg/min. CBF before the cardiopulmonary bypass was 30.6 +/- 5.5 ml/100 g brain/min, and increased to 33.8 +/- 8.9 ml/100 g brain/min during the cardiopulmonary bypass. CBF was proportional to systemic flow rate (r = 0.62, p less than 0.01) and showed poor association with blood pressure ranged from 35 to 94 mmHg. As for the relationship between innominate arterial and cerebral blood flow rate, CBF linearly followed the decrease of innominate arterial flow rate to below about 9 ml/kg/min, but showed almost no changes when innominate arterial flow rate was over 9 ml/kg/min. It was observed that cerebral oxygen consumption did not decrease significantly under moderate hypothermia (26-28 degrees C), as far as CBF of 25 ml/100 g brain/min was maintained. Based on the relationship between innominate arterial and cerebral blood flow rate, it was shown that the innominate arterial flow rate to provide CBF of 25 ml/100 g brain/min was 5.5 ml/kg/min.(ABSTRACT TRUNCATED AT 250 WORDS)

Adolescent↗

PubMed1986

Fetal volume blood flow and umbilical artery flow velocity waveform analysis: a comparison.

The estimation of fetal umbilical vein and aortic volume blood flow was compared with umbilical artery flow velocity-time waveform analysis in 42 pregnancies. The volume blood flow measurements were made with a combined linear array B-mode and pulsed Doppler ultrasound system. The umbilical artery flow velocity-time waveform analysis was made with either pulsed or continuous wave 2 MHz Doppler ultrasound and the systolic/diastolic (A/B) ratio was used as an index of flow resistance. There was no difference when continuous wave was compared to pulsed Doppler ultrasound as a method of recording flow velocity waveforms. Analysis of the umbilical artery flow velocity-time waveform was more sensitive (100%-50%) than the measurement of umbilical vein volume blood flow (ml/kg/min) in the detection of the small-for-gestational age (SGA) fetus. The predictive value of a positive test was higher (71%-45%) while specificity was similar (88%-81%). Descending aortic volume flow was reduced in only one SGA fetus. The increase in umbilical placental downstream resistance (high systolic/diastolic ratio) was associated with a reduction in the percentage of fetal aortic blood flow directed to the umbilical placental circulation.

Adult↗

PubMed1985

Quantification of pulsatile flow during cardiopulmonary bypass to permit direct comparison of the effectiveness of various types of "pulsatile" and "nonpulsatile" flow.

The relative merits of adding a "pulsatile" component to flow during cardiopulmonary bypass (CPB) has long generated controversy, the resolution of which has been hampered by lack of quantification of the "pulsatility" delivered by different devices. The present experimental series had two goals: to quantify the "pulsatility" of blood flow during CPB in terms of pulse rate and pulsatility index (PI) and to examine which aspects of a "pulsed flow" provide clinical benefits. A flow waveform can be expressed in terms of its baseline rate and its PI, the sum of the square of its harmonics components divided by the square of the mean flow. We used PI to quantify the pulsatility of blood flow in the descending thoracic aorta and used changes in the serum lactate level as an indication of end organ flow. In one experimental series seven adult mongrel dogs were placed on roller pump CPB at a constant flow of 100 ml/kg/min. After a 20-minute stabilization period a roller pump wave and three different pulse shapes (generated by a computer-controlled hydraulic pump) were evaluated for 15 minutes each. The pulse wave shapes were graded, with C being the sharpest and A the least sharp. In a second series six other dogs were placed on CPB and were subjected to roller pump perfusion and three pulse waves of identical shape but at different rates. The results indicated that a combination of a minimum PI of 1.88 and a minimum rate of 80 bpm were necessary to significantly reduce lactate production as compared with roller pump perfusion. Thus the same mean flow can have very different physiologic effects depending on how it is delivered. This quantification method permits direct comparison of different "pulsatile waveforms" and provides a means for identification of optimal pulsatile flow.

Animals↗

PubMed1983

Validity of Doppler measurements of anterior cerebral artery blood flow velocity: correlation with brain blood flow in piglets.

Continuous wave Doppler ultrasonography through the anterior fontanel has recently been used to assess changes in cerebral blood flow in human neonates. There has been controversy concerning whether measurements of Doppler blood flow velocity indeed correlate with brain blood flow. An in vivo correlation was performed between brain blood flow as measured by the microsphere method and Doppler flow velocity measurements of the cerebral arteries via an artificial fontanel in young piglets. The peak systolic velocity (r = .76, P less than .001), end diastolic velocity (r = .72, P less than .001) and area under the velocity curve (r = .86, P less than .001) all showed significant positive correlations with brain blood flow. The pulsatility index did not correlate with brain blood flow. Although continuous wave Doppler flow velocity measurements of the anterior cerebral artery cannot quantitatively assess cerebral blood flow, this methodology can be used to correlate changes in cerebral blood flow and provide a meaningful trend analysis following physiologic or pharmacologic perturbation of the cerebral circulation.

Animals↗

PubMed1994

Coronary blood flow autoregulation and flow heterogeneity in the stunned heart.

We used an anesthetized swine model of regionally "stunned" myocardium to determine the effect of stunning on coronary autoregulation and blood flow heterogeneity. In 18 domestic swine, stunning was accomplished by reducing blood flow to the left anterior descending coronary artery (LAD) by approximately 75% of baseline for 15 min and restoring it to normal for 1 hour. We quantified coronary autoregulation using both the slope of coronary pressure-flow curves and an autoregulation index. We quantified blood flow heterogeneity using radioactive microspheres to determine the variability in flow (dispersion index) among forty 200 mg segments of myocardium from the center of the stunned, LAD-perfused left ventricle. Before and after stunning, we measured autoregulation, myocardial blood flow and flow heterogeneity, as well as hemodynamic indices of myocardial oxygen demand. Fifteen min of ischemia and 1 hour of reperfusion produced both a 46% reduction in mechanical function, and a 7% drop in systemic arterial pressure, but not change in heart rate or rate pressure product. Myocardial oxygen consumption was 15% reduced and myocardial blood flow 16% reduced in the stunned myocardium when measured at one hour of reperfusion. Fifteen min after reperfusion, the slope of the coronary pressure flow plots and the coronary venous oxygenation were increased whereas the autoregulation index decreased. These findings all indicate reduced autoregulation during early reperfusion. However, after one hour of reperfusion, the slope of the coronary pressure-flow relation (0.41 +/- 0.19 vs. 0.48 +/- 0.26 ml.100 g-1.min-1.mmHg-1) and the autoregulation index (0.43 +/- 0.16 vs. 0.30 +/- 0.32) were unchanged from control measurements (p > 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed1995

Residence time in niches of stagnant flow determines fibrin clot formation in an arterial branching model--detailed flow analysis and experimental results.

Deposition of blood components in branching flow has been investigated primarily with regard to platelets. We instead examined thrombin-induced fibrin clot formation in separated laminar as well as turbulent branching flow. The most rapid clot growth and largest clot was obtained at the lowest inflow rate. Increased inflow reduced the clot size and turbulence completely prevented clot formation. Examination of corresponding flow conditions revealed the recirculation zone in laminar flow to be characterized by two stationary, counterrotating vortices. Niches of stagnant flow, exhibiting long residence times, low wall shear rates and characterized by convergent flow, were spared between the bulk flow and these vortices. Here, fibrin clot growth continued even when shear rates were increased more than 100-fold. Our results indicate that, in branching flow, the long residence times and convergent flow characteristic of flow niches rather than shear rate are critical for fibrin clot formation.

Arteries↗

PubMed1993

Cine magnetic resonance imaging and color Doppler flow mapping displays of flow velocity, spatial acceleration, and jet formation: a comparative in vitro study.

To study the effects of flow acceleration and high-velocity jets on the display characteristics of cine magnetic resonance imaging compared with color Doppler flow mapping, a custom-designed in vitro flow model was developed. This model consisted of a funnel segment tapering to an orifice (0.78 cm2) that leads into a confined receiving chamber with a second, discrete orifice (0.78 cm2) at its distal end. Cine magnetic resonance images obtained at varying flow rates (1.5 to 27.2 L/min) demonstrated loss of signal intensity throughout the tapering zone of spatial acceleration and a small zone of more marked signal loss immediately proximal to the second orifice (always < 50% of the signal intensity within the tapering funnel zone) associated with more rapid spatial acceleration. A formed jet was imaged distal to the first orifice, and the turbulence area surrounding the laminar central jet core correlated well with flow rate (r = 0.98), as did the distance from the orifice to the subsequent onset of flow relaminarization (r = 0.96). A turbulent spray area was always seen distal to the second, discrete orifice. Comparative observations with color Doppler flow mapping and continuous wave Doppler demonstrated that signal intensity on cine magnetic resonance imaging is reduced by both spatial acceleration, and the high-velocity and turbulent jets associated with obstructive and regurgitant lesions. In vitro evaluation of cine magnetic resonance imaging allows comparative observations to be made about the flow characteristics of cine magnetic resonance imaging and color Doppler flow mapping and provides a more rational basis for the interpretation of cine magnetic resonance imaging in the clinical setting.

Blood Flow Velocity↗

PubMed1997

Demonstration of fetal coronary blood flow by Doppler ultrasound in relation to arterial and venous flow velocity waveforms and perinatal outcome--the 'heart-sparing effect'.

This longitudinal observational study evaluates the stage at which coronary flow can be visualized by color-coded and pulsed wave Doppler sonography in fetuses with normal cardiac anatomy. Fetal biometry, echocardiography and Doppler examination of the umbilical and middle cerebral arteries, ductus venosus, inferior vena cava and umbilical vein were performed in 109 cases. Fetuses were divided into five groups based on the Doppler examination of the umbilical artery, birth weight and the ability to visualize coronary blood flow. Coronary blood flow was identified in six of 55 fetuses with normal growth who had normal Doppler studies and perinatal outcome. In these, visualization of coronary blood flow was possible after 31 weeks' gestation at a median gestational age of 37 weeks. Coronary blood flow was also visualized in ten of 54 fetuses with severe intrauterine growth retardation and highly pathological flow velocity waveforms in all vessels soon after a significant increase of venous indices in the inferior vena cava and ductus venosus. In these cases, coronary blood flow was identified at a significantly earlier gestational age (median 27 weeks). These fetuses had a poor perinatal outcome (average birth weight less than 3rd centile, mortality rate 50%, significantly lower umbilical artery blood pH and Apgar scores after 1 and 5 min). Intrauterine fetal death occurred in five fetuses after a median of 3.5 days following visualization of coronary blood flow. Median coronary peak blood flow velocities in the right coronary artery were higher in intrauterine growth-retarded than appropriate-for-gestational-age fetuses.

Blood Flow Velocity↗

PubMed2002

Modeling tree water flow as an unsaturated flow through a porous medium.

The electric circuit analogy has had a profound influence on how tree physiologists measure, model and think about tree water flow. For example, previous models that attempt to account for changes in saturation use the electric circuit analogy to define capacitance as the change in saturation per change in pressure. Given that capacitance is constant, this relationship implies that subjecting a block of wood to a pressure of -2.5 MPa for 2 min results in the same change in saturation as subjecting the same block to the same pressure for 2 days. Given the definition of capacitance, it is unclear how the electric circuit analogy could be used to predict changes in saturation separately from changes in pressure. The inadequacies in the electric circuit analogy discussed in this paper necessitate a new theory of tree water flow that recognizes the sapwood as being a porous medium and explicitly deals with the full implications of the unsaturated flow occurring in the sapwood. The theory proposed in this paper combines the Cohesion theory with a mathematical theory of multiphase flow through porous media. Based on this theory, both saturated and unsaturated tree water flow models are presented. Previous partial differential equation models of tree water flow based on the electric circuit analogy are shown to be mathematically equivalent to the model of saturated porous flow. The unsaturated model of tree water flow explicitly models the pressure profile and the rates of change in saturation and specific interfacial area (a measure of how the water in the unsaturated sapwood is partitioned between mobile and immobile components). The unsaturated model highlights the differences between saturated and unsaturated flow and the need to measure the variables governing tree water flow at higher spatial and temporal resolutions.

Models, Biological↗

PubMed1993

Difference in regional hepatic blood flow in liver segments--non-invasive measurement of regional hepatic arterial and portal blood flow in human by positron emission tomography with H2(15)O.

Organ blood flow can be quantitatively measured by positron emission tomography (PET). As the liver has dual blood supplies, arterial and portal, regional hepatic blood flow had not been measured quantitatively. However, we succeeded in simultaneously measuring both regional hepatic arterial and portal blood flow by PET in non-stressed patients. Mean regional portal hepatic blood flow in patients with normal liver and cirrhotic liver was 57.5 and 36.7 ml/minutes/100 g, respectively. Mean regional arterial blood flow was 42.5 and 30.7 ml/minutes/100 g, respectively. A significant difference between regional portal hepatic blood flows in normal and cirrhotic patients was noted. Mean regional portal hepatic blood flow in the lateral, medial, anterior, and posterior segments of the liver was 29.8, 43.4, 50.0, and 40.9 ml/minutes/100 g, respectively. Mean regional arterial blood flow in each liver segment was 37.6, 30.0, 28.2, and 31.6 ml/minutes/100 g, respectively. A significant difference between regional portal hepatic blood flows in lateral and anterior segment was noted. The p value was less than 0.025 and the 95% confidence interval of the difference between means was from -20.2 to -2.7 ml/minutes/100 g by ANOVA. These results showed that regional hepatic blood flow is not the same in all the liver segments.

Adult↗

PubMed1995

Comparison of pressure-derived fractional flow reserve with poststenotic coronary flow velocity reserve for prediction of stress myocardial perfusion imaging results.

The physiologic importance of coronary stenoses can be assessed indirectly by stress myocardial perfusion imaging or directly by translesional pressure and flow measurements. The aims of this study were to compare myocardial fractional flow reserve (FFRmyo), a recently proposed index of lesion significance derived from hyperemic translesional pressure gradients, with directly measured poststenotic flow velocity reserve for the prediction of myocardial perfusion stress imaging results in corresponding vascular beds. Poststenotic coronary flow velocity (0.018-inch guide wire) and translesional pressure gradients (2.7F fluid-filled catheter) were measured at baseline and after intracoronary adenosine (12 to 18 micrograms) in 70 arteries (diameter stenosis: mean 56% +/- 15%, range 14% to 94% by quantitative angiography). Coronary flow reserve was calculated as the ratio of hyperemic to basal mean flow velocity. FFRmyo was calculated during maximal hyperemia as equal to 1-(hyperemic gradient [mean aortic pressure-5]), where 5 is the assumed central venous pressure. Positive and negative predictive values and predictive accuracy for reversible stress myocardial perfusion abnormalities were computed. There was a significant correlation between pressure-derived FFRmyo and distal coronary flow reserve (r = 0.46; p < 0.0001). The strongest predictor of stress myocardial perfusion imaging results was the poststenotic coronary flow reserve (chi square = 33.2; p < 0.0001). The correlation between stress myocardial perfusion imaging and FFRmyo was also significant (chi square = 8.3; p < 0.005). There was no correlation between stress myocardial perfusion imaging and percentage diameter stenosis (chi square = 2.9; p = 0.10) or minimal lumen diameter (chi square = 0.47; p = 0.73). A poststenotic coronary flow reserve of < or = 2 had a positive predictive value of 89% for regionally abnormal myocardial perfusion imaging abnormalities, whereas the positive predictive values of FFRmyo and angiographic percentage diameter stenosis were only 71% and 67% respectively. In conclusion, the predictive value of poststenotic coronary flow velocity reserve for stress-induced myocardial perfusion abnormalities exceeds that of the translesional FFRmyo. These findings should be considered when applying these techniques for clinical decision making in the assessment of coronary stenosis severity.

Adult↗

PubMed1982

Comparative effects of nitroglycerin and nifedipine on myocardial blood flow and contraction during flow-limiting coronary stenosis in the dog.

Both nifedipine and nitroglycerin are used to treat angina pectoris. The comparative effects of these agents on myocardial blood flow and contraction in the setting of flow-limiting coronary stenosis are poorly understood. Thus 24 open chest dogs underwent carotid to left anterior descending coronary arterial perfusion with coronary flow probe and perfusion pressure monitoring. Segment length was measured with ultrasonic crystals in the subendocardial ischemic and nonischemic zones. Myocardial blood flow was measured with radioactive microspheres. Partial coronary occlusion was performed to attain a diastolic perfusion pressure of 40 mm Hg. Twelve dogs received intravenous nifedipine, 3 micrograms/kg per min, and 12 received intravenous nitroglycerin to reduce aortic pressure by 20 mm Hg. Partial occlusion resulted in a slight but significant decrease in segment shortening in the ischemic zone. Neither nitroglycerin nor nifedipine affected shortening in the ischemic zone. After occlusion, blood flow decreased in the subendocardial ischemic zone but was unchanged in the subepicardium. Nifedipine increased subendocardial blood flow in the nonischemic zone and decreased it in the ischemic zone but caused no change in subepicardial flow in the ischemic zone. In contrast, nitroglycerin decreased subendocardial and subepicardial blood flow in both the ischemic and nonischemic zones. In the setting of coronary stenosis, different classes of vasodilators may have varying effects on myocardial blood flow, suggesting different sites and mechanisms of action. In addition, segment function may not always reflect changes in myocardial blood flow.

Animals↗

PubMed1996

Chronic nonpulsatile blood flow. III. Effects of pump flow rate on oxygen transport and utilization in chronic nonpulsatile biventricular bypass.

The relationship between blood flow and oxygen transport was studied in five calves with chronic nonpulsatile biventricular bypass. Seven days was allowed for recovery from the effects of anesthesia and operation; the natural heart was then fibrillated. Pump flows were maintained at nominal rates of 90, 100, or 120 ml.kg-1.min for 1 week each, with the sequence varied from experiment to experiment. Venous and arterial blood samples were taken at rest for blood gas analysis. Serum lactate analysis was done twice a week, on the third and seventh days after each pump flow change. Serum catecholamine levels were assayed on the seventh day of each flow rate. Progressive exercise tests were also conducted during each test segment. Basal oxygen consumption of a 4-month-old calf was 6.3 +/- 0.3 ml.kg-1.min-1. The mixed venous oxygen tension decreased when pump flow rate was reduced (29.6 +/- 1.0, 28.3 +/- 1.2, and 23.8 +/- 0.9 mm Hg at 120, 100, and 90 ml.kg-1.min-1 of pump flow, respectively), and oxygen extraction increased linearly when pump flow rate was reduced. Hemoglobin concentration significantly affected oxygen extraction rate. Serum lactate concentration increased significantly at a 90 ml.kg-1.min-1 perfusion compared with concentrations at other pump flow rates (7.81 +/- 2.42 mEq/L at 90 ml.kg-1.min-1 vs 0.71 +/- 0.19 and 0.73 +/- 0.81 mEq/L at 100 and 120 ml.kg-1.min-1, respectively; p < 0.01, analysis of variance, Scheffe F test). Maximum oxygen extraction during exercise was 78%. These results suggest that a critical flow level between 90 and 100 ml.kg-1.min-1 maintains oxidative metabolism in the calf with chronic nonpulsatile flow. The resulting oxygen delivery was slightly higher than that indicated in the literature. Maximal oxygen extraction was normal.

Animals↗

PubMed2003

Effect of geometric structure of flow promoting agents on the flow properties of pharmaceutical powder mixture.

PURPOSE: The object of this work was to investigate the mechanism of how the surface geometric structure of flow agents affects on the flowability of pharmaceutical powder mixtures. METHODS: Nonporous and porous silicas were mixed with directly compressible fillers as flow promoting agents. The geometric structure of flow agents was investigated by gas adsorption and laser diffraction analysis. Flowability was evaluated with Carr's index measurement. Adhesion force between fillers and flow agents was determined using atomic force microscopy. RESULTS: Flowability was improved with the addition of both nonporous and porous flow agents. In the case of nonporous flow agents, effect to promote flowability decreased with the increase of particle diameter, whereas porous flow agents highly improved flowability independent of particle diameter. Atomic force microscopy measurement found that the adhesion force between a porous agent and filler was smaller than that between a nonporous agent and filler. CONCLUSIONS: Enhancement of flowability varies depending on the geometric structure of flow agents. Porous flow agents improve flow properties more than nonporous agents, because porosity is highly contributed to reduction of adhesion force between particles.

Pharmaceutical Preparations↗

PubMed2005

Dynamic protein adsorption in microchannels by "stop-flow" and continuous flow.

This work addresses two ways of loading proteins on microchannel surfaces for immunoassay applications: the "stop-flow" and the continuous flow processes. The "stop-flow" method consists of successive static incubation periods where the bulk solution depletes upon the adsorption process. In the present paper, a multi-step "stop-flow" protein coating is studied and compared to a coating under continuous flow conditions. For the "stop-flow", a non-dimensional parameter is here introduced, indicating the adsorbing capacity of the system, by which it is possible to calculate the number of loads necessary to reach the optimum coverage. For the continuous flow, the effects on the adsorption of the kinetic rates, flow velocity and wall capacity have been considered. This study shows the importance of a careful choice of the fluid velocity to minimise the sample waste. For diffusion controlled and kinetics controlled processes, two flow velocity criteria are provided in order to obtain the best possible coverage, with the same amount of sample as with the "stop-flow".

Adsorption↗

PubMed1994

Abnormalities of left ventricular flow following mitral valve replacement: a colour flow Doppler study.

Left ventricular flow patterns were studied at rest by colour flow Doppler echocardiography in 33 patients with mitral tilting-disc prostheses (group 1), in 38 patients with mitral tissue prostheses (group 2) and in 18 healthy volunteers (controls). A 'crossed' flow pattern was seen in 14 patients with mechanical (42%) and in 15 patients with tissue prostheses (39%). The remaining patients and all controls had either 'parallel' or 'intermediate' flow patterns which were classified as 'normal'. There was a significant correlation between the type of flow pattern and the position of the mitral prosthesis in both study groups. The presence of a crossed flow pattern, however, was not related to functional status (assessed clinically by NYHA class) or to abnormalities on the electrocardiogram. Left atrial size was greater in patients with crossed flow than in those without, but all other echocardiographic parameters were similar. Eight patients with crossed and eight with normal flow patterns underwent treadmill exercise testing; there was no difference between the two groups with regard to exercise performance as determined by exercise duration, maximum oxygen consumption and the ventilatory response to exercise. The results of this study indicate that the pattern of blood flow within the left ventricle may be fundamentally altered by the orientation of both mechanical and tissue prostheses. The presence of a crossed flow pattern is not, however, accompanied by significant deleterious haemodynamic or functional consequences.

Adult↗

PubMed1991

Differences in cerebral blood flow between alpha-stat and pH-stat management are eliminated during periods of decreased systemic flow and pressure. A study during cardiopulmonary bypass in rabbits.

Prior reports suggest cerebral blood flow (CBF) responses to changing bypass (systemic) flow rates may differ between alpha-stat and pH-stat management. To compare the effect of blood gas management upon CBF responses to changing systemic flow and pressure, 15 New Zealand White rabbits, anesthetized with fentanyl and diazepam, underwent nonpulsatile cardiopulmonary bypass at 25 degrees C. One group of animals (n = 8) was randomized to alpha-stat blood gas management that maintained arterial carbon dioxide tension (PaCO2) approximately 40 mmHg when measured at 37 degrees C. A second group (n = 7) was managed with pH-stat technique, maintaining PaCO2 approximately 40 mmHg when corrected to the animal's actual temperature. Bypass was initiated at a flow rate of 100 ml.kg-1.min-1 and, after approximately 20 min, control hemodynamic and CBF measurements (radioactive microspheres) were made. Thereafter, bypass flow rate was changed in random order at 15-min intervals to 50, 70, and 100 ml.kg-1.min-1. CBF and hemodynamic measurements were repeated at the end of each period of altered bypass flow. Groups differed significantly with respect to both pHa and PaCO2. There were no significant differences between groups with respect to bypass flow rate, mean arterial pressure (MAP), central venous pressure, temperature, hematocrit, arterial oxygen tension (PaCO2), or bypass duration at any measurement point. MAP decreased significantly, from approximately 80 to approximately 65 mmHg with decreasing bypass flow (P = 0.0001). Over the entire range of bypass flows, CBF decreased with decreasing bypass flow (P = 0.001), and the degree of change was equivalent among regions and between groups.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed2000

Restoration of flow-dependent coronary dilation by ACE inhibition improves papaverine-induced maximal coronary blood flow in hypertensive patients: demonstration that large epicardial coronary arteries are more than conductance vessels.

Restoration of flow-dependent coronary artery dilation by angiotensin-converting enzyme inhibition (ACEI) has been demonstrated in patients with hypertension. The aim of the present study was to evaluate whether dilation of conductance coronary arteries may alter maximal coronary blood flow (CBFmax) and minimal coronary resistance (CRmin) in hypertensive patients with reversible impairment of flow-dependent coronary artery dilation. Thirteen hypertensive patients with angiographically normal coronary arteries and no other risk factors were studied. Cross-sectional areas (CSAs) of proximal and distal left anterior descending (LAD) coronary arteries were determined by quantitative angiography. Coronary flow velocity was recorded in the distal LAD with an intracoronary Doppler catheter. Estimates of coronary blood flow and resistance were calculated at rest and during maximal increase in blood flow induced by papaverine injected in the midportion of the LAD, both before and after ACEI. Flow-dependent dilation of the proximal LAD, abolished before ACEI, was restored after (26.7 +/- 11.2%; p < 0.001). The increase in CSA of the distal LAD exposed to papaverine was significantly higher after ACEI than before (from 33.4 +/- 20.5% to 51.5 +/- 23.4%; p < 0.001). After restoration of proximal LAD flow-dependent dilation, CBFmax was increased by +21.0 +/- 10.3% (p < 0.001), and CRmin was reduced by 19.3 +/- 9.5% (p < 0.001). Thus, dilation of epicardial coronary arteries participates substantially in the coronary resistance in hypertensive patients. Restoration of flow-dependent coronary artery dilation by ACEI may improve the ability of coronary circulation to deliver its maximal myocardial blood flow in hypertensive patients.

Angiotensin-Converting Enzyme Inhibitors↗