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PubMed1995

Functional hepatic flow and Doppler-assessed total hepatic flow in control subjects and in patients with cirrhosis.

Functional hepatic flow and total hepatic flow were determined by non-invasive techniques in 32 patients with cirrhosis and in 32 paired control subjects. Functional hepatic flow was measured by the hepatic clearance of D-sorbitol, while total hepatic flow was determined by pulsed echo-Doppler, as the sum of portal and hepatic arterial blood flow. Functional hepatic flow was significantly reduced in patients with cirrhosis (927 +/- 314 vs. 1287 +/- 315; p < 0.0001), while total hepatic flow was slightly increased (1511 +/- 540 vs. 1261 +/- 321 in controls; p = 0.028). In control subjects functional hepatic flow significantly correlated with total hepatic flow (r = 0.823; p < 0.001), while no correlation was observed in cirrhosis. Functional hepatic flow and the difference between total hepatic flow and functional hepatic flow significantly correlated with the Child-Pugh score in patients with cirrhosis. The data obtained in control subjects support the measurement of functional hepatic flow and total hepatic flow by non-invasive techniques. The finding that in cirrhosis functional hepatic flow is significantly decreased, while Doppler-assessed total hepatic flow is preserved or even increased, confirms that a relevant part of blood flowing through the liver is diverted by intrahepatic shunts. The simultaneous assessment of these two parameters by non-invasive techniques may be proposed as a reliable tool for the study of functional shunting of cirrhosis.

Adult↗

PubMed2001

The effects of flow rate, length and external pressure upon the pressure required for fluid to flow through a ureter.

OBJECTIVE: To determine in vitro the effects of increments of external pressure on the pressure required to conduct fluid through ureters of various lengths at different flow rates, as the flow of a fluid through a collapsible tube is influenced by various factors (e.g. external pressure, the pressure gradient between the ends, the length and diameter of the tube, and the viscosity of fluid). MATERIALS AND METHODS: Two in vitro systems were designed, composed of three parts, i.e. a perfusion line, an exit line and a container of two different widths in which short or long ureteric segments, obtained from cattle, could be placed; the ureter was connected to the perfusion and exit lines. Physiological saline was added to the container until the desired external pressure was applied to the ureter. The flow pressure (height of the perfusion line) was recorded when producing flows through ureters of varying length at 1.5 and 6 mL/min, and determined under various external pressures. The intra-ureteric pressure during flow was also monitored by a pressure transducer. The four combinations of long and short ureters with high and low flow rates were compared using analysis of variance, with the Pearson correlation coefficient used to evaluate the relationships between the various pressures. RESULTS: There were close relationships between flow pressure and external pressure (r = 0.727), intra-ureteric and external pressure (r = 0.766), and the flow pressure and intra-ureteric pressure (r = 0.940, all P < 0.001). Increments in external pressure resulted in greater flow and intra-ureteric pressure (P < 0.05). Increases in flow pressure were more pronounced than increases in intra-ureteric pressure at the same external pressure (P < 0.05) at high flow rates. A longer ureter and higher flow rates caused greater intra-ureteric pressure (P < 0.05). CONCLUSION: External pressure increases the pressure required to conduct fluid through a ureter and the effect is more pronounced at high flow rates. The length of the ureter also affects the flow pressure at high flow rates. Therefore, flow through the ureter follows the Poiseuille equation only at high flow rates. Thus, increases in intra-abdominal pressure may cause greater intrapelvic pressure and induce ureteric obstruction, contributing to the pathogenesis of hydronephrosis.

Animals↗

PubMed1975

Venous flow velocity, venous volume and arterial blood flow.

The relationship of arterial blood flow and venous volume to venous flow velocity was studied in normal subjects. The effects of current modes of treatment in venous thrombosis and of a vasodilator drug on venous flow velocity were also investigated. Total calf flow and venous volume were measured by venous occlusion plethysmography while venous flow axial velocity was determined by the transit time of 131-I albumin from calf to inguinal region. Local intravenous epinephrine administration induced venoconstriction and increased venous flow velocity. Intra-arterial isoproterenol and angiotensin increased and decreased arterial flow, respectively, with no change in venous flow velocity of volume, but local heat increased arterial flow and venous flow velocity with no change in venous volume. Local cold, despite venoconstriction, decreased venous flow velocity accompanied by a decreased arterial flow. Intravenous heparin did not affect venous flow velocity. Intravenous but not oral nylidrin increased venous flow velocity. Therefore venous flow velocity can be significantly increased by venocontriction, by large increases in arterial flow (local heat), and by a parenteral vasodilator drug. These experiements indicate that there is a basis for applying heat but not cold in the prevention and treatment of venous thrombosis.

Adult↗

PubMed2003

Evaluation of blood flow in carotid artery stenosis using B-flow sonography.

B-flow ultrasonography can directly visualize blood streams by reflecting the intravascular red blood cells, and so can detect turbulent flow in vessels. B-flow sonography was used to evaluate flow abnormalities in patients with cervical carotid artery stenosis, and to investigate the mechanism of large embolus formation that may cause distal arterial occlusion. Twenty-two patients with > or = 60% stenosis of the cervical carotid artery excluding cardiovascular embolism were examined by B-flow and color Doppler sonography. Two patients had distal embolism as revealed by digital subtraction angiography, 16 patients had lacunar infarction, and four patients had transient ischemic attacks. B-flow sonography demonstrated reverse flow at the poststenotic site in patients with > or = 70% stenosis. Increased echogenicity at the site of the stenosis was seen in patients with at least 80% stenosis. Prestenotic reverse flow was seen in nine patients with > or = 85% stenosis. The two patients with distal embolism had decreased echogenicity and flow velocity, and diastolic flow was absent. B-flow sonography could detect various turbulent flow patterns and changes in echogenicity associated with cervical carotid artery stenosis. Prestenotic reverse flow and decreased flow velocity may be potential causes of distal embolism. B-flow sonography is a useful method for the evaluation of flow abnormality in patients with carotid artery stenosis.

Aged↗

PubMed2003

Comparison of intraoperative transit-time flow measurement with early postoperative magnetic resonance flow mapping in off-pump coronary artery surgery.

The purpose of this prospective study was to evaluate graft patency of off-pump coronary artery surgery intraoperatively by transit-time flow measurement and to compare this technique with postoperative magnetic resonance flow mapping. Twenty patients (13 men and 7 women; mean age, 679 +/- 76 yr) underwent off-pump coronary artery surgery. Intraoperative transit-time flow measurement of grafts was performed measuring maximum, minimum, and mean flows. For each graft, the pulsatile index was calculated by dividing the difference between the maximum and the minimum flow by the mean flow In the early postoperative period (1st week), magnetic resonance flow mapping was performed using phase contrast flow quantification. Mean intraoperative flow values and mean magnetic resonance flow mapping values were compared. At the same postoperative session, contrast-enhanced magnetic resonance angiography was performed to evaluate graft patency. In 20 patients, a total of 49 coronary graft flows were assessed with intraoperative transit-time flow measurement and postoperative magnetic resonance flow mapping. Upon comparison, there was a strong correlation between techniques, with stable and statistically significant differences between the intraoperative and postoperative flow mapping values. One saphenous vein graft was revised intraoperatively, due to graft failure. Our data suggest that the combined use of intraoperative transit-time flow measurement and postoperative magnetic resonance flow analysis has a potential role in the assessment of graft patency in off-pump coronary artery surgery although more study is required.

Aged↗

PubMed1996

Flow patterns in dog aortic arch under a steady flow condition simulating mid-systole.

To elucidate the possible connection between blood flow and localized pathogenesis and the development of atherosclerosis in humans, we studied the flow patterns and the distribution of fluid axial velocity and wall shear stress in the aortic arch in detail. This was done by means of flow visualization and high-speed cinemicrographic techniques, using transparent aortic trees prepared from the dog. Under a steady flow condition at inflow Reynolds numbers of 700-1600, which simulated physiologic conditions at early- to mid-systole, slow, spiral secondary, and recirculation flows formed along the left anterior wall of the aortic arch and at the entrance of each side branch adjacent to the vessel wall opposite the flow divider, respectively. The flow in the aortic arch consisted of three major components, namely, an undisturbed parallel flow located close to the common median plane of the arched aorta and its side branches, a clockwise rotational flow formed along the left ventral wall, and the main flow to the side branches, located along the right dorsal wall of the ascending aorta. Thus, looking down the aorta from its origin, the flow in the aortic arch appeared as a single helical flow revolving in a clockwise direction. Regions of low wall shear stress were located along the leading edge of each side branch opposite the flow divider where slow recirculation flows formed, and along the left ventral wall where slow spiral secondary flows formed. If we assume that the flow patterns in the human aortic arch well resemble those observed in the dog, then it is likely that atherosclerotic lesions develop preferentially at these sites of low wall shear stress in the same manner as in human coronary and cerebral arteries.

Animals↗

PubMed2006

Dynamic particle image velocimetry flow analysis of the flow field immediately downstream of bileaflet mechanical mitral prostheses.

New dynamic particle image velocimetry (PIV) technology was applied to the study of the flow field associated with prosthetic heart valves. Four bileaflet prostheses, the St. Jude Medical (SJM) valve, the On-X valve with straight leaflets, the Jyros (JR) valve, and the Edwards MIRA (MIRA) valve with curved leaflets, were tested in the mitral position under pulsatile flow conditions to find the effect of the leaflet shape and overall valve design on the flow field, particularly in terms of the turbulent stress distribution, which may influence hemolysis, platelet activation, and thrombus formation. Comparison of the time-resolved flow fields associated with the opening, accelerating, peak, and closing phases of the diastolic flow revealed the effects of the leaflet shape and overall valve design on the flow field. Anatomically and antianatomically oriented bileaflet valves were also compared in the mitral position to study the effects of the orientation on the downstream flow field. The experimental program used a dynamic PIV system utilizing a high-speed, high-resolution video camera to map the true time-resolved velocity field inside the simulated ventricle. Based on the experimental data, the following general conclusions can be made. High-resolution dynamic PIV can capture true chronological changes in the velocity and turbulence fields. In the vertical measuring plane that passes the centers of both the aortic and mitral valves (A-A section), bileaflet valves show clear and simple circulatory flow patterns when the valve is installed in the antianatomical orientation. The SJM, the On-X, and the MIRA valves maintain a relatively high velocity through the central orifice. The curved leaflets of the JR valve generate higher velocities with a divergent flow during the accelerating and peak flow phases when the valve is installed in the anatomical orientation. In the velocity field directly below the mitral valve and normal to the previous measuring plane (B-B section), where characteristic differences in valve design on the three-dimensional flow should be visible, the symmetrical divergent nature of the flow generated by the two inclined half-disks installed in the antianatomical orientation was evident. The SJM valve, with a central downward flow near the valve, is contrasted with the JR valve, which has a peripherally strong downward circulation with higher turbulent stresses. The On-X valve has a strong central downward flow attributable to its large opening angle and flared inlet shape. The MIRA valve also has a relatively strong downward central flow. The MIRA valve, however, diverts the flow three-dimensionally due to its peripherally curved leaflets.

Heart Valve Prosthesis↗

PubMed1978

alpha- and beta-receptor blockade of isoproterenol- and norepinephrine-induced effects on regional blood flow and blood flow acceleration.

The effects of the beta-receptor blocking agent propranolol (100 microgram/kg i.v.) and of the alpha-receptor blocking agent dihydroergotamine (50 microgram/kg i.v.) on hemodynamic responses to isoproterenol and norepinephrine (both 1--1024 ng/kg) were investigated in anesthetized dogs. The effects studied were: (1) flow in the ascending aorta and the coronary, common hepatic, gastroduodenal, splenic, cranial mesenteric, renal and femoral arteries: (2) maximal flow acceleration in the splenic, cranial mesenteric and femoral arteries; (3) maximal rate of change of left ventricular pressure (LV dP/dt max). Propranolol shifted the dose-response curves for the isoproterenol-induced flow increases in the common hepatic, gastro-duodenal, and cranial mesenteric arteries to the right. It did not influence the flow responses to isoproterenol in the ascending aorta or the coronary, splenic, renal and femoral arteries. Propranolol prevented the decrease of arterial pressure evoked by isoproterenol. Propranolol shifted the isoproterenol-induced increase of LV dP/dt max and maximal blood flow to the same extent. Propranolol blocked the flow to the liver and gastrointestinal tract to a greater extent than the LV dP/dt max and maximal flow acceleration. Propranolol had no effect on the norepinephrine-induced increases in flow in the splenic, femoral and coronary arteries, but blocked the norepinephrine-evoked increases of flow accelerations and LV dP/dt max to the same extent. Dihydroergotamine inhibited the norepinephrine-induced increase in flow in the femoral artery and the decreases in flow in the hepatic, splenic, cranial mesenteric and renal arteries, and reversed the reduction of flow in the gastroduodenal artery. It is argued that dihydroergotamine may inhibit the increase in femoral flow through two mechanisms: (1) blocking the flow reduction to norepinephrine in the abdomen, and thereby passively shunting blood from the abdomen in preference to the femoral bed; (2) attenuating the norepinephrine-evoked reflexogenic femoral vasodilatation. It is concluded that: (1) propranolol is a beta-receptor blocking agent with a preference for blockade of isoproterenol-induced vascular effects; (2) norepinephrine-induced flow increases are not direct actions on vascular beta-receptors; (3) the increase of maximal blood flow accelerations after isoproterenol and norepinephrine is mediated by stimulation of cardiac beta-receptors; (4) dihydroergotamine is an alpha-receptor blocking agent particularly in the splanchnic vascular region.

Adrenergic alpha-Antagonists↗

PubMed1993

Automated flow rate calculations based on digital analysis of flow convergence proximal to regurgitant orifices.

OBJECTIVES: The purpose of the study was to develop and validate an automated method for calculating regurgitant flow rate using color Doppler echocardiography. BACKGROUND: The proximal flow convergence method is a promising approach to quantitate valvular regurgitation noninvasively because it allows one to calculate regurgitant flow rate and regurgitant orifice area; however, defining the location of the regurgitant orifice is often difficult and can lead to significant error in the calculated flow rates. To overcome this problem we developed an automated algorithm to locate the orifice and calculate flow rate based on the digital Doppler velocity map. METHODS: This algorithm compares the observed velocities with the anticipated relative velocities, cos psi/2 pi r2. The orifice is localized as the point with maximal correlation between predicted and observed velocity, whereas flow rate is specified as the slope of the regression line. We validated this algorithm in an in vitro model for flow through circular orifices with planar surroundings and a porcine bioprosthesis. RESULTS: For flow through circular orifices, flow rates calculated on individual Doppler maps and on an average of eight velocity maps showed excellent agreement with true flow, with r = 0.977 and delta Q = -3.7 +/- 15.8 cm3/s and r = 0.991 and delta Q = -4.3 +/- 8.5 cm3/s, respectively. Calculated flow rates through the bioprosthesis correlated well but underestimated true flow, with r = 0.97, delta Q = -10.9 +/- 12.5 cm3/s, suggesting flow convergence over an angle > 2 pi. This systematic underestimation was corrected by assuming an effective convergence angle of 212 degrees. CONCLUSIONS: This algorithm accurately locates the regurgitant orifice and calculates regurgitant flow rate for circular orifices with planar surroundings. Automated analysis of the proximal flow field is also applicable to more physiologic surfaces surrounding the regurgitant orifice; however, the convergence angle should be adjusted. This automated algorithm should make quantification of regurgitant flow rate and regurgitant orifice area more reproducible and readily available in clinical cardiology practice.

Algorithms↗

PubMed1997

Simultaneous determination of aortic valve area by the Gorlin formula and by transesophageal echocardiography under different transvalvular flow conditions. Evidence that anatomic aortic valve area does not change with variations in flow in aortic stenosis.

OBJECTIVES: The purpose of this study was to determine the impact of changes in flow on aortic valve area (AVA) as measured by the Gorlin formula and transesophageal echocardiographic (TEE) planimetry. BACKGROUND: The meaning of flow-related changes in AVA calculations using the Gorlin formula in patients with aortic stenosis remains controversial. It has been suggested that flow dependence of the calculated area could be due to a true widening of the orifice as flow increases or to a disproportionate flow dependence of the formula itself. Alternatively, anatomic AVA can be measured by direct planimetry of the valve orifice with TEE. METHODS: Simultaneous measurement of the planimetered and Gorlin valve area was performed intraoperatively under different hemodynamic conditions in 11 patients. Left ventricular and ascending aortic pressures were measured simultaneously after transventricular and aortic punctures. Changes in flow were induced by dobutamine infusion. Using multiplane TEE, AVA was planimetered at the level of the leaflet tips in the short-axis view. RESULTS: Overall, cardiac output, stroke volume and transvalvular volume flow rate ranged from 2.5 to 7.3 liters/min, from 43 to 86 ml and from 102 to 306 ml/min, respectively. During dobutamine infusion, cardiac-output increased by 42% and mean aortic valve gradient by 54%. When minimal flow was compared with maximal flow, the Gorlin area varied from (mean +/- SD) 0.44 +/- 0.12 to 0.60 +/- 0.14 cm2 (p < 0.005). The mean change in Gorlin area under different flow rates was 36 +/- 32%. Despite these changes, there was no significant change in the planimetered area when minimal flow was compared with maximal flow. The mean difference in planimetered area under different flow rates was 0.002 +/- 0.01 cm2 (p = 0.86). CONCLUSIONS: By simultaneous determination of Gorlin formula and TEE planimetry valve areas, we showed that acute changes in transvalvular volume flow substantially altered valve area calculated by the Gorlin formula but did not result in significant alterations of the anatomic valve area in aortic stenosis. These results suggest that the flow-related variation in the Gorlin AVA is due to a disproportionate flow dependence of the formula itself and not a true change in valve area.

Adrenergic beta-Agonists↗

PubMed1998

Assessment of coronary blood flow in humans using phase difference MR imaging. Comparison with intracoronary Doppler flow measurement.

Coronary blood flow quantification provides essential information on the hemodynamic significance of coronary artery stenoses. Recently, magnetic resonance (MR) flow mapping has emerged as a new promising method to noninvasively determine flow velocity and flow volume within the coronary arteries. The aim of this study was to compare phase difference (PD) MR flow quantification with intracoronary Doppler flow measurements in 15 patients with suspected or known coronary artery disease. Flow quantification was attempted before and after systemic application of 5mg Isosorbiddinitrate (ISDN) in order to determine possible alterations in coronary flow volume. PD MR flow mapping was performed successfully in 13 of the 15 patients. For flow velocities and flow volume values, a close correlation between PD MR and Doppler flow measurements was found (r = 0.79 and r = 0.90, respectively). However, average flow measured by PD MR was significantly lower than the invasively obtained values (9.0 +/- 4.4 cm/sec vs. 11.7 +/- 4.9 cm/sec; p < 0.001 and 46.3 +/- 28.7 ml/min vs. 53.4 +/- 32.8 ml/min; p < 0.05). Although the mean flow volume remained constant in the entire patient group after ISDN application, individual changes (increase in 6, decrease in 4 cases) could be documented with PD MR imaging and showed a good correlation to the Doppler method (r = 0.82). In conclusion, PD MR flow mapping is a promising method for the noninvasive quantification of coronary blood flow and therefore offers the potential of assessing coronary artery stenoses. However, technical improvements are mandatory in order to increase accuracy of the method.

Blood Flow Velocity↗

PubMed1995

Accuracy of breath-by-breath analysis of flow-volume loop in identifying sleep-induced flow-limited breathing cycles in sleep apnoea-hypopnoea syndrome.

1. Inspiratory flow limitation is involved in the pathophysiology of sleep-related breathing disorders. Since the definition of flow-limited cycle is based on a dissociation between flow and respiratory efforts, identification of inspiratory flow limitation requires upper airway or intrathoracic pressure measurements. We examined the accuracy of the analysis of the flow-volume loop of a tidal breath in identifying inspiratory flow limitation during sleep in ten patients with a sleep apnoea-hypopnoea syndrome. 2. Measurements were taken during continuous positive airway pressure trials. After data acquisition, the presence of inspiratory flow limitation was identified by the presence of an inspiratory plateau or decrease in inspiratory flow independently of the increase in inspiratory efforts. The flow-volume loop was reconstructed for each breathing cycle by plotting the instantaneous flow and the tidal volume. The instantaneous inspiratory and expiratory flows were measured at 50% of the respective portion of the tidal volume, and a breath-by-breath analysis of the mid-tidal volume-flow ratio (inspiratory/expiratory ratio) was obtained. The analysis of the flow-volume loop was compared with standard inspiratory flow limitation criteria using different values of the inspiratory/expiratory ratio threshold, below which breathing cycles were classified as flow-limited. With a lower limit of the normal inspiratory/expiratory ratio threshold of 0.97, the sensitivity and specificity of the method were both 76%. In each subject, the proportion of breathing cycles identified as flow-progressively decreased with an increasing positive pressure level.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗

PubMed2001

Do changes in blood flow in the subclavian artery affect flow volume in IMA grafts after complete arterial revascularization with the T-graft technique?

BACKGROUND: The T-graft procedure achieves complete arterial coronary revascularization with only two conduits. In this technique, all the bypass anastomoses are supplied by the left internal mammary artery (IMA). Changes in flow conditions or flow redistribution in the subclavian artery may thus sigificantly influence coronary perfusion. The objective of this study was to determine whether changes in blood flow in the subclavian artery affect the flow in IMA grafts in patients who have undergone complete arterial revascularization with T-grafts. METHODS: Quantitative flow volume and flow profiles in the IMA graft and the proximal subclavian artery were measured with a flow-wire in 20 patients one week postoperatively. Following baseline measurements, brachial artery constriction was achieved by applying a blood pressure measurement cuff to the patient's left upper arm. After 5 minutes, quantitative flow in the IMA and in the proximal subclavian artery was assessed. The cuff was then released and the measurements repeated. RESULTS: Flow in the subclavian artery changed significantly (p < 0.01) from baseline (355.4 +/- 95.2 ml/ min) to constriction (171.2 +/- 61.3 ml/min) and hyperemia (679.3 +/- 195.1 ml/min). Flow in the IMA graft remained constant irrespective of subclavian artery flow (75.4 +/- 26.2 ml/min vs. 78.0 +/- 28.9 ml/min vs. 75.5 +/- 29.3 ml/min, respectively). The flow profile in the IMA was similarily unchanged. CONCLUSION: In patients in whom the coronary bypass blood flow is dependent on the left IMA, neither the quantitative flow volume nor the flow profile are altered by changes in blood flow of the subclavian artery.

Aged↗

PubMed2004

Coronary flow and flow reserve in children.

Aortic blood pressure affects coronary blood flow, but within the normal physiological blood pressure range coronary blood flow is constant. The coronary flow is pulsatile, being maximal in the early diastole. There is a smaller systolic flow component. The low systolic pressure in the right ventricle favours systolic flow. The proportion of systolic flow is greater in the right than in the left coronary artery. Heart diseases in children cause several haemodynamic and functional changes that are likely to affect myocardial perfusion. Newborns with severe valvular aortic stenosis may have a retrograde systolic flow in the left coronary artery. Children with dilated cardiomyopathy have a reduced coronary flow related to myocardial mass. Coronary flow reserve (CFR) is defined as the ratio of maximal coronary blood flow, as induced by reactive hyperaemia or administration of vasodilators, divided by resting flow. Coronary flow can normally increase 2.5-4-fold. CFR is reduced if basal flow is increased due to myocardial hypertrophy, strain or hypoxaemia. Very low CFR values measured with positron emission tomography are reported in neonates with surgically treated congenital heart disease. Measurement of coronary flow velocity with the intracoronary Doppler guide wire may be regarded as a reference or "gold standard" in the evaluation of coronary flow velocity and CFR. Coronary flow and CFR in children is a largely unexploited field, and has vast potential for future research.

Age Factors↗

PubMed1994

Cerebral blood flow during low-flow hypothermic cardiopulmonary bypass in baboons.

BACKGROUND: Neurologic injury after cardiopulmonary bypass (CPB) is a frequent and devastating complication of cardiothoracic surgery. Disordered cerebral hemodynamics during CPB has been implicated as an important factor in the etiology of these injuries. Evidence of disordered cerebral hemodynamics includes reports of a progressive time-dependent decrease in cerebral blood flow (CBF) during stable full-flow CPB. Low-flow hypothermic CPB has become a preferred technique for the management of pediatric patients undergoing surgical repair of complex cardiac lesions. Because CBF is already substantially reduced with the onset of low-flow CPB, we determined if a similar progressive decline in CBF occurs during the low-flow state. METHODS: After induction of general anesthesia in seven baboons, CPB was instituted. alpha-Stat management of arterial blood gases was used. Animals were cooled at a pump flow rate of 2.5 l.min-1.m-2 until tympanic membrane temperature decreased to 18 degrees C. CPB flow was then reduced to 0.5 l.min-1.m-2 and maintained constant for at least 77 min. Thereafter, CPB flow was increased to 2.5 l.min-1.m-2 and baboons rewarmed to normal temperature. CPB was discontinued after return of cardiac function. CBF was measured before, during and after CPB by washout of intraarterial xenon 133. RESULTS: Low-flow CPB resulted in a decrease in CBF to about 50% of the prebypass rate and about 30% of the value measured during full-flow CPB. Sequential measurements of CBF at 30-min intervals during low-flow CPB showed no time-dependent change in cerebral perfusion. CONCLUSIONS: Although systemic flow is reduced to 20% of full-flow during low-flow CPB, CBF reduced by half is disproportionately preserved relative to systemic flow. Furthermore, there is no time-dependent change in CBF under these low-flow conditions.

Animals↗

PubMed1998

Visualization of flow patterns from stents and stent-grafts in an in vitro flow-model.

RATIONALE AND OBJECTIVES: The authors determine flow characteristics and pressure gradients of different stents and stent grafts in an in vitro flow-model. METHODS: Five vascular stents (Memotherm, Cragg, two Palmaz P308, Strecker, and Wall) and one stent graft (Cragg EndoPro System 1), equal in length (60 mm) and diameter (10 mm), were deployed in a closed flow-model. The inner diameter of the tube measured 9 mm. Flow at 1.5 L/min, 6 L/min, and 10 L/min was simulated. Flow patterns were visualized by anionic particles illuminated with two Helium-Neon lasers. Laminary flow characteristics and pre-/poststent pressure gradients were determined in either expanded stent, 25% stenosis, or 50% stenosis. RESULTS: Stent implantation induced a decrease of laminary flow compared with an unstented tube with and without concentric 25% stenosis (P < 0.01) at all flow rates and an increase of pressure gradients compared with an unstented tube for flow rates greater than 1.5 L/min (P < 0.01) (except for Cragg EndoPro System 1 stent, which revealed an increase of the pressure gradient at a flow rate of 1.5 L/min [P < 0.01]). Memotherm stent permitted maximum of laminary flow at all flow rates and stenoses (expanded: 79.50% at 1.5 L/min to 69.90% at 10 L/min; P < 0.01). Memotherm and Palmaz permitted lowest pressure gradients (P < 0.01). All of the endoprostheses demonstrated laminary flow at 50% stenosis. CONCLUSIONS: The investigated stents and stent grafts showed different severity of flow disturbances and pressure gradients at different graded stenoses. Inadequate stent depolyment bears the risk of creating less laminary flow and pathologic pressure gradients. Because flow disturbances and pressure gradients may influence neointimal hyperplasia, stent design and completeness of stent unfolding are important regarding the appearance of postinterventional restenoses.

Analysis of Variance↗

PubMed1999

Sodium nitroprusside increases human skeletal muscle blood flow, but does not change flow distribution or glucose uptake.

1. The role of blood flow as a determinant of skeletal muscle glucose uptake is at present controversial and results of previous studies are confounded by possible direct effects of vasoactive agents on glucose uptake. Since increase in muscle blood flow can be due to increased flow velocity or recruitment of new capillaries, or both, it would be ideal to determine whether the vasoactive agent affects flow distribution or only increases the mean flow. 2. In the present study blood flow, flow distribution and glucose uptake were measured simultaneously in both legs of 10 healthy men (aged 29 +/- 1 years, body mass index 24 +/- 1 kg m-2) using positron emission tomography (PET) combined with [15O]H2O and [18F]fluoro-2-deoxy-D-glucose (FDG). The role of blood flow in muscle glucose uptake was studied by increasing blood flow in one leg with sodium nitroprusside (SNP) and measuring glucose uptake simultaneously in both legs during euglycaemic hyperinsulinaemia (insulin infusion 6 pmol kg-1 min-1). 3. SNP infusion increased skeletal muscle blood flow by 86 % (P < 0.01), but skeletal muscle flow distribution and insulin-stimulated glucose uptake (61.4 +/- 7. 5 vs. 67.0 +/- 7.5 micromol kg-1 min-1, control vs. SNP infused leg, not significant), as well as flow distribution between different tissues of the femoral region, remained unchanged. The effect of SNP infusion on blood flow and distribution were unchanged during infusion of physiological levels of insulin (duration, 150 min). 4. Despite a significant increase in mean blood flow induced by an intra-arterial infusion of SNP, glucose uptake and flow distribution remained unchanged in resting muscles of healthy subjects. These findings suggest that SNP, an endothelium-independent vasodilator, increases non-nutritive, but not nutritive flow or capillary recruitment.

Adult↗

PubMed2000

Differences between blood flow as indicated by the hemodialysis blood roller pump and blood flow measured by an ultrasonic sensor.

BACKGROUND/AIM: The ultrasonic transit time is currently the best method for measuring the blood flow rate in the extracorporeal hemodialysis circuit. The purpose of this study was to analyze the differences between blood flow as indicated by the hemodialysis blood roller pump (prescribed blood flow) and by an ultrasonic flowmeter (delivered blood flow). METHODS: The ultrasonic blood flow was measured in 20 patients on chronic hemodialysis who were dialyzed through an arteriovenous fistula. During each dialysis session the ultrasonic blood flow was measured at three different blood roller pump flow rates (300, 350, and 400 ml/min). In order to analyze the influence of inflow and outflow pressures on blood flow, this study was conducted during nine consecutive dialysis sessions during which needles of different sizes were used. RESULTS: The ultrasonic flow was always lower than indicated by the blood roller pump: 265+/-12, 304+/-15, and 341+/- 19 ml/min for blood roller pump flow rates of 300, 350, and 400 ml/min, respectively (variability: -11.6, -13.1, and -14.8%, respectively). An univariate regression analysis showed that the reduction in flow recorded ultrasonically correlated with both venous blood line pressure (r = -0.2679, p<0.001) and negative arterial blood line pressure (r = 0. 6773, p<0.001). By multivariate analysis, only the arterial blood line pressure has a predictive value. When all measurements were grouped by arterial blood line pressure ranges, the variability between ultrasonic blood flow and blood roller pump flow was found to be similar in those groups with the same arterial blood line pressure, regardless of the blood roller pump flow rate. CONCLUSIONS: The blood flow indicated by the dialysis blood roller pump is always greater than the delivered blood flow, and this difference is in turn conditioned by the negative pressure induced by the blood roller pump in the arterial blood line.

Blood Flow Velocity↗