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PubMedDate not supplied

An electrical analogue for a pressure-controlled, fluid flow generator for arterial blood-flow simulation.

To study the human arterial system, we constructed a pressure-controlled, fluid flow generator [1] that allows simulation of pressure and flow waves in a hydraulic system in which the arteries are simulated by collapsible tubes. In this paper we elaborate an electrical analogue of this flow generator. The analogue circuit contains only five electrical components: a source resistance and inductance, and a downstream resistance, inductance and capacitance. The values of the components are obtained from a function fit to the pressure and flow waves generated during steady and pulsatile flow measurements. The pulsation and relaxation times calculated from the analogue model are compared with experimental values. This electrical analogue allows computer simulation of the arterial pressure and flow waves.

Arteries↗
PubMed1993

Comparison of various agents in contrast enhancement of color Doppler flow images: an in vitro study.

The commercially manufactured contrast agents, Echovist and Albunex, were compared with sonicated conventional agents, indocyanine green, 29% renografin-60, 0.9% normal saline and 25% mannitol in their ability to enhance color Doppler flow signals. In a pneumatically regulated pulsatile flow system, a glycerine, saline (0.9%) and sand (5 microns particle size) solution was imaged using a 2.5 MHz phased-array transducer. Four different flow velocities (0.40, 0.35, 0.30 and 0.25 m/s) as measured by color Doppler guided pulse Doppler were utilized. All color Doppler settings were kept constant throughout the study. Utilizing a power injector, four different volumes (1.0, 1.5, 2.0 and 2.5 mL) of each contrast agent were injected into the flow medium at various transducer angles (20, 30, 40 and 60 degrees) and various distances from the transducer (3.38, 5.5, 6.76 cm). For Echovist and Albunex, several concentrations varying from 2% to 100% were used. Keeping instrument settings constant, color flow areas obtained before and after each contrast injection were planimeterized and the percent increase in the color flow area computed and compared. At full (100%) concentration, 20 degrees transducer angle and a flow velocity of 0.40 m/s, the maximum increase in the color flow area was 568%, 251%, 180%, 110%, 71%, and 38% for Echovist, Albunex, sonicated indocyanine green, renografin, normal saline and mannitol, respectively. However, a significant reduction in the degree of color flow enhancement was observed, with decreases in the concentration of these agents, and increases in the Doppler beam incident angle or distance from the transducer. Increasing the flow velocity of the medium into which contrast was injected did not produce significant changes in the contrast enhancement effect for all agents except Echovist. Increasing the injection volume significantly increased the color flow area for sonicated agents but not for Echovist or Albunex. This preliminary in vitro study shows that the commercially manufactured contrast agents, Echovist and Albunex, are much superior to sonicated conventional contrast agents in the enhancement of color Doppler flow signals. Of the sonicated agents, indocyanine green had the best enhancement capability.

Blood Flow Velocity↗
PubMed2002

Surface integration of velocity vectors from 3D digital colour Doppler: an angle independent method for laminar flow measurements.

BACKGROUND: The study was designed to test the angle independence of a dynamic three-dimensional digital colour Doppler method for laminar flow measurement. The technique acquired three-dimensional data by rotational acquisition and used surface integration of Doppler vector velocities and flow areas in time and space for flow computation. METHOD: A series of pulsatile flows (peak flow 55-180 ml/s) through a curved tube were studied with reference flow rates obtained using an ultrasonic flow meter. Colour Doppler imaging was performed at three angles to the direction of flow (20 degrees, 30 degrees, 40 degrees), using a multiplane transoesophageal probe controlled by an ATL HDI5000 system. Integration of digital velocity vectors over a curved three-dimensional surface across the tube for each of the 11 flow rates at each angle was performed off-line to compute peak flow. RESULTS: Peak flow rates correlated closely (r=0.99) with the flow meter with the mean difference from the reference being -0.8+/-2 x 4 ml/s, 0.9+/-2.6 ml/s, 1.0+/-2 x 3 ml/s for 20 degrees, 30 degrees and 40 degrees respectively. Comparison of the three angle groups showed no significant differences (P=0.15, ANOVA). When sampled obliquely, the flow area on the curved surface increased while the velocities measured decreased. CONCLUSION: Surface integration of velocity vectors to compute three-dimensional Doppler flow data is less angle dependent than conventional Doppler methods.

Blood Flow Velocity↗
PubMedDate not supplied

Determination of regurgitant flow and volume by integrating actual proximal velocities over hemispheres (IPROV) in two orthogonal planes.

The proximal acceleration technique is a promising technique for quantification of regurgitant valve flow. Although the shape of the regurgitant proximal isovelocity field has been shown to vary with orifice size, geometry, and driving pressure, normally the centerline velocity alone is used for estimation of flow. In this model study of pulsatile flow, two-dimensional and spectral Doppler data were transferred digitally to a computer in which proximal velocity fields were corrected for time and angle errors. With the purpose of improving accuracy, flow was estimated by integrating proximal velocities over nonisovelocity spheric control surfaces in the best zone of measurement (0.15 to 0.45 m/sec at an angle up to +/- 45 degrees from the center line) in two perpendicular planes. Three regurgitant volumes in the range of 5 to 21 ml were studied for circular (diameters of 4, 6, and 8 mm), crescent, and diagonal orifices. The quotient between effective orifice area, estimated by dividing peak flow with peak velocity in the vena contracta, and true orifice area (Aeff = Q(tm)/Vo(tm)) was 0.66 (range 0.60 to 0.79), 0.50 (0.48 to 0.52), and 0.67 (0.66 to 0.68) for the circular, crescent, and diagonal orifices, respectively. Regurgitant volume estimated by multiplying effective orifice area by the velocity-time integral in the vena contracta (V = Aeff.velocity-time integral) ranged from 92% to 115% of the true volume for the circular, 89% to 92% for the crescent, and 105% to 112% for the diagonal orifices, respectively. It is possible to calculate regurgitant volume correctly with data acquisition from multiple hemispheres and planes and postprocessing of data. This amendment of the proximal acceleration technique has great advantage over the center-line method, especially when the orifice is asymmetric.

Blood Flow Velocity↗
PubMed1993

Helical and retrograde secondary flow patterns in the aortic arch studied by three-directional magnetic resonance velocity mapping.

BACKGROUND: Helical and retrograde secondary flows have been recorded in the aorta, but their origins and movements in relation to the arch have not been clarified. We set out to do this using magnetic resonance velocity mapping. METHODS AND RESULTS: Three-directional phase contrast cine magnetic resonance velocity mapping was used to map multidirectional flow velocities in the aortas of 10 healthy volunteers. Computer processing was used to visualize flow vector patterns in selected planes. Right-handed helical flows predominated in the upper aortic arch in late systole, being clearly recognizable in 9 of the 10 subjects. Nonaxial components of velocity in this region reached 0.29 m/s (+/- 0.05 m/s) as axial velocities declined from a peak of 1.0 m/s (+/- 0.1 m/s). Helical flow patterns in the upper descending aorta varied between subjects, apparently depending on arch curvature. End-systolic retrograde flow originated from regions of blood with low momentum, usually along inner wall curvatures. Flow studies in a curved tubular phantom showed right-handed helical flow in the upper "arch" when the inflow section was positioned to simulate ascending aortic curvature, and retrograde flow occurred along the inner wall at end systole during pulsatile flow. CONCLUSIONS: Helical and retrograde streams are consistent features of intra-aortic flow in healthy subjects that result, at least in part, from the curvature of the arch and the pulsatility of flow in it. They may have significance in relation to circulatory dynamics and the pathogenesis of atheroma in the arch.

Adult↗
PubMed1992

Flow measurements in a highly curved atherosclerotic coronary artery cast of man.

Flow visualization and wall pressure measurements were made in a polyurethane cast of a cadaver coronary artery with a significant "s" shaped reverse curvature. A sucrose solution was used to simulate the kinematic viscosity of blood, with flow rates in the physiologic range. Flow visualization demonstrated significant secondary flow patterns in the wall vicinity, which increased with increasing Reynolds number. Random dye dispersion was observed at a Reynolds number of about 400, but not at 200. Dye filament patterns in the transition between the first and second curved region were predominantly influenced by the second curved region at lower Reynolds numbers, and by the first curved region at higher Re. Local wall pressure measurements demonstrated a significant centrifugal effect with large radial pressure differences across the casting. Flow resistances for the casting were considerably greater than reference Poiseuille flow values, and increased further with pulsatile flow.

Blood Pressure↗
PubMedDate not supplied

Development of a flow simulator to study haemodynamic behaviour of natural and artificial blood vessels under physiologic flow conditions.

A new computer-controlled flow simulator has been designed to study the haemodynamic behaviour of natural and artificial blood vessels under physiologic flow conditions. The simulator can generate well characterized and fully developed laminar flow properties. It includes a unique perfusion case that imposes an axial tension on the vessel segment, and a commercial programmable pump to reproduce pulsatile flow rates. Response to high frequency commands was greatly attenuated and displayed a frequency dependent phase angle. Thus, for complex pulsating flow rates containing different frequency components, the system response was significantly distinct from the command. To reproduce physiologic waveforms, the transfer function of the whole system was determined for different amplitudes and frequencies of flow rate excitations. Each input command was compared to the measured flow rate, and the values of the gain and phase angle were evaluated. If the desired flow rate was composed of a sum of n sine wave components, each has a frequency fj and an amplitude Aj, a corrected command signal was then reconstructed by amplifying the attenuated components and advancing those lagged in time. The corrected signal was finally applied as the new command to the pump. The results showed an excellent agreement with physiologic waveforms. Examples of different pulsatile flow experiments to investigate the effects of frequency, pressure, and wall elasticity are presented.

Blood Flow Velocity↗
PubMed1997

Requirement for accurate measurement of regurgitant stroke volume by the combined continuous-wave Doppler and color Doppler flow convergence method.

The examination conditions necessary for accurate measurement of regurgitant volume by the proximal flow convergence method applying a simple hemispheric equation remain uncertain. This study investigated the requirement for measuring regurgitant stroke volume from the combined continuous-wave and color Doppler proximal flow convergence approach. Twenty-five pulsatile flow rates were produced by driving five regurgitant stroke volumes ranging from 30 to 70 ml/beat through planar orifices with cross-sectional areas ranging from 0.10 to 1.0 cm2. Four different shaped orifices (circular, rectangular with a major/minor axis ratio 2:1, slitlike with a major/minor axis ratio of 8:1, and square) having identical orifice areas (0.5 cm2) were examined. Regurgitant volume (RV) was estimated from the combined continuous-wave and color Doppler approach according to the previously described equation RV = 2 pi x (r max)2 x AV x (TVI/Vmax), where r max is maximal radial distance, AV is aliasing velocity, TVI is time velocity integral of regurgitant jet, and Vmax is peak velocity of regurgitant jet. Plotting the difference between actual and calculated RV versus radial distance of the proximal convergence shell for each flow rate from circular to rectangular orifices yielded curves conforming to a curvilinear function that crossed the point of zero difference at 1.0 cm. However, in the slitilke orifice, a more remote distance (1.6 cm) is required for the best agreement. Actual regurgitant stroke volume can be estimated well by the combined continuous-wave Doppler and proximal flow convergence method applying a simple hemispheric equation if an aliasing velocity is used that results in a radial distance of at least 1.0 cm.

Confounding Factors, Epidemiologic↗
PubMed1985

The accuracy of Doppler ultrasound measurement of pressure gradients across irregular, dual, and tunnellike obstructions to blood flow.

The accuracy of Doppler-estimated pressure gradients in the setting of irregular, multiple, and tunnellike stenoses was investigated. An in vitro model of the left ventricular outflow tract was designed to allow pulsatile flow of red cells in saline across valve orifices from 0.01 to 2.5 cm2. Simultaneous pressure gradients were estimated by both Doppler and direct-pressure manometer techniques. Gradients obtained by the two methods correlated well for valve areas in the range of clinical stenoses at pressure gradients of 10 to 150 mm Hg (r = .97 to .99). Model valves were constructed with a large orifice (0.75 to 1.25 cm2) placed beside a small orifice (0.02 to 0.25 cm2) in the same outflow tract. A distinct jet was recorded when the Doppler transducer was aligned with each orifice. Doppler-estimated gradients for each pair of large and small orifices were identical and correlated well with those measured by manometer (r = .97 to .99). Irregularly shaped orifices also provided good correlation between the two methods (r = .98 to .99). Pulsatile flow was generated through long tunnellike obstructions with cross-sectional areas varying from 0.06 to 1.25 cm2. Tunnel length varied from 0.1 to 4 cm. Tunnel areas above 0.25 cm2 gave good Doppler-to-manometer correspondence at all tunnel lengths. Doppler underestimated manometer-determined values in the 0.25 cm2 tunnel by 8% at 3 cm and by 15% at 4 cm. In the 0.06 cm2 tunnel, Doppler underestimated manometer gradients by 12%, 15%, 32%, and 42% at lengths of 1, 2, 3, and 4 cm, respectively.(ABSTRACT TRUNCATED AT 250 WORDS)

Centrifugation, Density Gradient↗
PubMed1987

Phasic flow patterns at a hemodialysis venous anastomosis.

A phase-by-phase analysis of local flow patterns at the venous anastomosis of an arteriovenous hemodialysis angioaccess loop graft (AVLG) was made. The study was carried out in an elastic, transparent Silastic in vitro flow model, which duplicates the detail geometry of the AVLG obtained from an animal model (30+ kg dogs with 12 weeks bilateral femoral AVLG implantation). The flow model was installed in a mock pulsatile flow loop system designed to simulate physiological conditions. Flow visualization was made in laser-illuminated flow fields using a high-speed cine camera. Analysis of the high-speed cine indicates there is a distinct separation region downstream of the anastomotic toe in the median plane and a stagnation region that oscillates along the opposite wall. During inward motion of the vessel wall, accumulation of particles in the separation region and the nearby stagnation region is observed. A large swirl appears in the distal vein during end-systolic period. A double-helical flow pattern occurs further down in the distal vein. Retrograde flow in the distal vein occurs in an "oscillating" manner following each cardiac cycle.

Animals↗
PubMed1985

Localized real time blood flow measurements.

A novel method for real time, localized, flow measurements is applied to blood flow in human fingers. Results for arterial and venous flow in normal subjects and patients with abnormal blood circulation are presented. Effects of blood flow regulation by the autonomic nervous system have been observed. Stricture of the digital arteries could be clearly demonstrated in a patient with Raynaud's phenomenon. Experimental signals due to pulsatile flow in a model system can be simulated in a quantitative way. The calibration, however, depends on the actual spin-spin relaxation time and the shape of the pulsatile flow vs. time curve. Due to these limitations, the volume flow rate can be measured with a relative error of approximately +/- 25%.

Blood Flow Velocity↗
PubMed2000

Strategy for reduction of stroke incidence in coronary bypass patients with cerebral lesions. Early results and mid-term morbidity using pulsatile perfusion.

OBJECTIVES: Cerebral complication is an important factor affecting the outcome after coronary artery bypass surgery under cardiopulmonary bypass. One of the causes for cerebral complication is preoperative cerebrovascular stenotic lesion. Here, we have studied the effect of pulsatile perfusion on the rate of cerebral complication due to a cerebrovascular lesion in patients undergoing coronary arterial bypass graft under cardiopulmonary bypass. METHODS: 261 consecutive elective patients underwent operation using cardiopulmonary bypass for management of the atherosclerotic ascending aorta. Group 1 consisted of 62 patients with a cerebrovascular stenotic lesion (> or = 75%) identified on a magnetic resonance angiogram or multiple cerebral infarction diagnosed using a computer tomogram. Group 2 consisted of 199 patients diagnosed with no significant cerebral lesion. In Group 1, the systolic blood pressure during cardiopulmonary bypass was maintained at a level of 80 mmHg by means of pulsatile flow. In Group 2, non-pulsatile perfusion was used as usual. RESULTS: The overall hospital mortality was 1.5%, and no mortality was caused by a cerebral event. Only one patient in Group 1 suffered from temporary hemiparalysis. A cerebral complication occurred in only 1.6% in Group 1, and 0.4% overall. The actuarial freedom from cerebrovascular accident after 54 months was 84.4% in Group 1, and 96.2% in Group 2 (p = 0.0011). CONCLUSIONS: Management of the atherosclerotic ascending aorta and the use of pulsatile perfusion were helpful in preventing cerebral injury during CABG.

Aged↗
PubMed1982

Pulsatile reperfusion does not modify global myocardial ischemic injury.

In an attempt to arbitrate the reputed clinical efficacy of pulsatile flow during reperfusion in minimizing ischemic injury, 32 mongrel dogs supported by normothermic cardiopulmonary bypass were subjected to 30 minutes (Groups IC and IP) or 60 minutes (Groups IIC and IIP) of global myocardial ischemia. The effect of pulsatile flow (P) initiated during 30 minutes of reperfusion on the recovery of myocardial adenosine triphosphate (ATP) and creatine phosphate (CP) stores, coronary blood flow, and myocardial water content (MWC) was compared to the effect of linear reperfusion (C) in another group of animals. ATP stores, which significantly decreased to 43% and 53% of preischemic levels (Groups IC and IP, respectively, p less than 0.01) and 36% and 31% of control values (Groups IIC and IIP, respectively. p less than 0.001), did not increase with either pulsatile or linear reperfusion. CP stores, depleted 97% during ischemia in all groups, returned to preischemic levels regardless of the mode of reperfusion flow. Coronary blood flow measured 30 minutes after aortic unclamping was not significantly different from control flow in any group. MWC significantly decreased during ischemia from 80.5% +/- 0.8% to 76.5% +/- 1.1% in Group IC and from 81.8% +/- 1.2% to 76.8% +/- 0.8% in Groups IP (p less than 0.05) and returned to preischemic levels with reperfusion. However, following 60 minutes of ischemia, pulsatile reperfusion prevented the significant increase in MWC that accrued after linear reperfusion (80.7% +/- 1.5% to 84.0% +/- 0.7%, p less than 0.05). These data indicate that pulsatile reperfusion initiated after an ischemic injury that results in a 50% or greater depletion of myocardial ATP stores does not restore myocardial nucleotide levels or enhance coronary blood flow, although the pathological increase in MWC may be avoided.

Adenosine Triphosphatases↗
PubMed1994

[Normal findings with duplex sonography of liver blood vessels--experience in the examination of 100 patients with healthy livers].

100 patients of our kidney transplantation program and uneventful as regards their liver history were indexed by the pulsatile flow (PFI) of the hepatic artery and the damp curve (DI) of the hepatic veins. The average age of the patients was 36 years (20-50y). The pulsatile flow index (PFI) was calculated as 0.4 to 0.7. The damp index (DI) as 0.3 to 0.54. In 10 of these volunteers the measurement was performed 3 times per day for 5 days: there was no difference to be found in comparison to the values of the total group. The presented values of the PFI and DI give the normal range and will be the basis for further investigations in patients after liver transplantation or suffering from liver diseases.

Adult↗
PubMed2001

Validation of rapid velocity encoded cine imaging of a dynamically complex flow field using turbo block regional interpolation scheme for k space.

Block regional interpolation scheme for k space (BRISK) is a sparse sampling approach to allow rapid magnetic resonance imaging of dynamic events. Rapid velocity encoded cine (VEC) imaging with Turbo BRISK is potentially an important clinical diagnostic technique for cardiovascular diseases. Previously we applied BRISK and Turbo BRISK to imaging pulsatile flow in a straight tube. To evaluate the capabilities of Turbo BRISK imaging in more complex dynamic flow fields such as might exist in the human vasculature, an in vitro curved tube model, similar in geometry to the aortic arch, was fabricated and imaged under pulsatile flow conditions. Velocity maps were obtained using conventional VEC and Turbo BRISK (turbo factors 1 through 5). Comparison of the flow fields obtained with each higher order turbo factor showed excellent agreement with conventional VEC with minimal loss of information. Similarly, flow maps showed good agreement with the profiles from a laser Doppler velocimetry model. Turbo-5 BRISK, for example, allowed a 94% savings in imaging time, reducing the conventional imaging time from over 8 min to a near breath-hold imaging period of 31 s. Turbo BRISK shows excellent promise toward the development of a clinical tool to evaluate complex dynamic intravascular flow fields.

Biomedical Engineering↗
PubMed1988

A numerical study of flow in curved tubes simulating coronary arteries.

Numerical simulations of pulsatile flow in coronary arteries which take into account the curvature associated with the bending of arteries over the surface of the heart are presented for resting, excited and drug induced states. The study was motivated by reported observations of atherosclerotic plaque localization on the inner curvature of coronary arteries. The simulated flow field appears quasi-steady under resting conditions with wall shear stress always highest on the outside wall and only a single secondary flow vortex in the half tube. However, reversal of wall shear stress direction at the inside wall does occur under resting flow conditions and this is not a quasi-steady characteristic. The flow field is markedly unsteady under excited conditions with wall shear stress sometimes peaking on the inside wall and an increase in the magnitude of wall shear stress reversal on the inside wall. However, only a single secondary flow vortex in the half tube is observed. Implications of the simulations for the role of fluid mechanics in coronary artery atherosclerosis are also discussed.

Blood Flow Velocity↗
PubMed1989

The effects of pulsatile and non-pulsatile cardiopulmonary bypass on renal blood flow and function.

The physiologic effects of pulsatile and non-pulsatile flow in cardiopulmonary bypass were compared in terms of the relationship between different flow rates and what effects these had on pulsatile and non-pulsatile flow. Forty adult mongrel dogs were used in this study and divided into 5 groups, each comprised of 8 animals, according to the flow rate during cardiopulmonary bypass, namely; 40, 60, 80, 100, or 120 ml/kg/min. The animals were perfused with either pulsatile or non-pulsatile flow for 1 hour, given randomly at the same mean flow rate. At flow rates of 80 and 100 ml/kg/min, the mean arterial blood pressure and total peripheral vascular resistance were significantly lower in pulsatile flow than in non-pulsatile flow, and the renal blood flow was significantly greater in pulsatile flow than in non-pulsatile flow. The renal arterial-venous lactate difference was significantly less in pulsatile flow than in non-pulsatile flow at a flow rate of 80 ml/kg/min, and the renal lactate extraction was significantly higher in pulsatile flow than in non-pulsatile flow at the same flow rate. The renal excess lactate was significantly lower in pulsatile flow than in non-pulsatile flow at a flow rate of 100 ml/kg/min. There were no significant differences in these parameters between the two types of perfusion at flow rates of 40, 60 or 120 ml/kg/min. Pulsatile flow was therefore apparently advantageous, when compared to non-pulsatile flow, in terms of hemodynamics, renal circulation, and metabolism of the kidney at flow rates of 80 and 100 ml/kg/min. However, when the flow rate was 120 ml/kg/min, pulsatile flow and non-pulsatile flow had the same effects.

Animals↗
PubMed1997

The relation between pump flow rate and pulsatility on cerebral hemodynamics during pediatric cardiopulmonary bypass.

OBJECTIVES: Neurologic impairment, at least partly ischemic in origin, has been reported in up to 25% of infants undergoing cardiopulmonary bypass, with or without circulatory arrest. Controversy continues about the effect of pump flow, pulsatile or nonpulsatile, on the brain and in particular on cerebral blood flow. This study examines the relationship between pump flow rate and cerebral hemodynamics during pulsatile and nonpulsatile cardiopulmonary bypass. METHOD: Near-infrared spectroscopy was used to determine cerebral blood flow and cerebral blood volume (measured as concentration change) in a randomized crossover study. Pulsatile and nonpulsatile flow were used for six 5-minute intervals at each of three different pump flow rates (0.6, 1.2, and 2.4 L x m2 x min(-1)) in 40 patients, median age 2 months (range 2 weeks to 20 years 5 months). The relations between pulsatile flow, pump flow rate, cerebral blood flow, hemoglobin concentration change (cerebral blood volume), mean arterial pressure, arterial carbon dioxide tension, and hematocrit value were prospectively examined by means of multivariate analysis. RESULTS: Cerebral blood flow decreased 36% per L x m(-2) x min(-1) decrease in pump flow rate and was associated with changes in mean arterial pressure but did not differ according to pulsatility. Change in hemoglobin concentration was unrelated to changes in pulsatility of pump flow. CONCLUSION: Cerebral blood flow is related to pump flow rate. Pulsatile flow delivered with a Stöckert pump does not increase cerebral blood flow or alter hemoglobin concentration during cardiopulmonary bypass in children.

Blood Volume↗