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PubMed1988

Flow measurements in a human femoral artery model with reverse lumen curvature.

Flow visualization and wall pressure measurements were made in a smooth reverse curvature model that conformed to the gentle "s" shape of a left femoral artery angiogram of a patient in a clinical trial. Observed lesion localization at the inner (lesser) curvatures appeared to be associated with secondary flows in the wall vicinity directed toward the inner curvatures that tended to reverse direction in the flow entering the reverse curvature region. Moderate flow resistance increases of about 20 percent above the Poiseuille flow relation were found at the higher physiological Reynolds numbers Re above about 600-700 and thus Dean numbers for steady flow. For pulsatile flow simulation, flow resistances did not increase up to the largest Re of 470 tested. Apparently, the large variations in velocity during the cardiac cycle disrupted the stronger secondary flow patterns observed at the higher Reynolds numbers for steady flow.

Arteriosclerosis↗
PubMed1991

Validation of a quantitative radiographic technique to estimate pulsatile blood flow waveforms using digital subtraction angiographic data.

We have validated a new radiographic technique for determining pulsatile volume flow in arteries following an intraarterial injection of contrast material. Instantaneous blood velocities were estimated by generating a parametric image from dynamic angiographic images in which the image grey level represents contrast material concentration as a function of time and distance along a vessel segment. Adjacent concentration--distance profiles in the parametric image were shifted with respect to distance until a match occurred. A match was defined as the point where the sum of squares of the differences in the two profiles was a minimum. The distance translated per frame interval gives the instantaneous contrast material bolus velocity. We have validated the technique using an experimental phantom of blood circulation, consisting of a pump, flexible plastic tubing, the tubular probe of an electromagnetic flowmeter (EMF) and a solenoid, to simulate a pulsatile flow waveform, which includes reverse flow. Small boluses of contrast material can be injected at various positions in the circuit. Measurements of pulsatile velocity flow were taken at 40 ms intervals, using a tube of 6.6 mm internal diameter and an imaged tube length of 200 mm. The shape of the flow velocity waveform was faithfully reproduced but there was an overestimation of peak velocity of 40% at low velocities (peak velocity of 540 mm s-1), reducing to 19% at peak velocities of 964 mm s-1 with an underestimation of 16% at the peak velocities of 1899 mm s-1. The validation was repeated for distances ranging from 130 to 230 mm between injection and measurement sites and for imaged tube lengths varying from 200 to 20 mm.(ABSTRACT TRUNCATED AT 250 WORDS)

Aged↗
PubMed1997

Alkaline phosphatase in osteoblasts is down-regulated by pulsatile fluid flow.

It is our hypothesis that interstitial fluid flow plays a role in the bone remodeling response to mechanical loading. The fluid flow-induced expression of three proteins (collagen, osteopontin, and alkaline phosphatase) involved in bone remodeling was investigated. Rat calvarial osteoblasts subjected to pulsatile fluid flow at an average shear stress of 5 dyne/cm2 showed decreased alkaline phosphatase (AP) mRNA expression after only 1 hour of flow. After 3 hours of flow, AP mRNA levels had decreased to 30% of stationary control levels and remained at this level for an additional 5 hours of flow. Steady flow (4 dyne/cm2 fluid shear stress), in contrast, resulted in a delayed and less dramatic decrease in AP mRNA expression to 63% of control levels after 8 hours of flow. The reduced AP mRNA expression under pulsatile flow conditions was followed by reduced AP enzyme activity after 24 hours. No changes in collagen or osteopontin mRNA expression were detected over 8 hours of pulsatile flow. This is the first time fluid flow has been shown to affect gene expression in osteoblasts.

Alkaline Phosphatase↗
PubMed1978

Non-invasive electromagnetic measurement of the peripheral pulsatile blood flow: experimental study and clinical applications.

The non-invasive electromagnetic blood flowmeter described in this paper allows us to measure pulsatile flow through a limb. The limb is placed in a magnetic field and the blood flow rate induces electromagnetic forces which are detected at the skin surface with ECG electrodes (Faraday's law). A special computer technique is necessary to isolate the signal from artefacts (local ECG, BCG, EMG). In vitro calibration is performed using a circulatory model and in vivo using mongrel dogs. Its validity is assessed by comparing the results with the responses obtained from the invasive electromagnetic flowmeter. Sources of error in the measurement such as blood composition (Na+, K+), haematocrit (45% to 29%), and venous flow are reported here. The results indicate that the method is reliable, easy to utilise and offers a unique non-invasive way of measuring true pulsatile blood flow rate in humans. Various clinical applications are discussed for possible use of the device.

Animals↗
PubMed2005

Pulsatile blood flow in the polypoidal choroidal vasculopathy.

OBJECTIVE: To describe patients with pulsatile polypoidal vessels in polypoidal choroidal vasculopathy (PCV). DESIGN: Retrospective, observational case series. PARTICIPANTS: Eighty-four eyes of 74 patients with PCV. METHODS: The medical records of patients diagnosed with PCV between 1998 and 2004 at Kagoshima University Hospital were reviewed. MAIN OUTCOME MEASURES: A pulsatile polypoidal vessel (PV) on indocyanine green angiography (ICGA). RESULTS: Seven of 74 patients (9.5%) had PVs in the macula. Four eyes revealed pulsatile PVs on the day the diagnosis of PCV was first made, and PVs in the other 3 eyes showed pulsatile movement during the follow-up period. Two patterns of pulsatile movement were observed on ICGA: (1) a rhythmic variation in the caliber of a choroidal vessel (caliber variation pattern) and (2) a pulsatile blood flow in a tortuous and relatively narrow choroidal vessel (pulsatile blood flow pattern). Both patterns of pulsatile PVs appeared in the early frames of the ICGA, and some of them were observable even during the first 15 minutes after the ICG dye injection. The pulsatile movement disappeared spontaneously without treatment in some patients, and the period in which pulsatile PVs was detectable on ICGA was limited in each patient. CONCLUSIONS: We report the features of pulsatile PV in PCV. It is a unique and important characteristic that has not been reported with any other chorioretinal diseases and may provide a clue to understanding the pathogenesis of PCV.

Aged↗
PubMed2006

Numerical simulations of pulsatile blood flow using a new constitutive model.

In the present paper we use a new constitutive equation for whole human blood [R.G. Owens, A new microstructure-based constitutive model for human blood, J. Non-Newtonian Fluid Mech. (2006), to appear] to investigate the steady, oscillatory and pulsatile flow of blood in a straight, rigid walled tube at modest Womersley numbers. Comparisons are made with the experimental results of Thurston [Elastic effects in pulsatile blood flow, Microvasc. Res. 9 (1975), 145-157] for the pressure drop per unit length against volume flow rate and oscillatory flow rate amplitude. Agreement in all cases is very good. In the presentation of the numerical and experimental results we discuss the microstructural changes in the blood that account for its rheological behaviour in this simple class of flows. In this context, the concept of an apparent complex viscosity proves to be useful.

Blood Flow Velocity↗
PubMed1991

[The rapid magnetic resonance tomography measurement of the contrast medium dilution kinetics (gadolinium-DTPA) in a circulatory phantom].

We studied first-pass MRI contrast dilution to compute flow and volume of distribution in a realistic flow phantom. Pulsatile flow was provided by a one-chamber artificial heart. Physiological stroke volume, rate, pressure, and flow were adjustable. An elastic tube with dimensions similar to that of the human aorta was imaged at a rate of 2.4 Hz. After contrast injection, an initial increase in signal intensity was followed by a decrease. Signal-intensity time plots demonstrated slightly skewed curves as expected from dispersion theory. After calibration at different gadolinium-DTPA concentrations, signal intensities were converted into true gadolinium concentrations, and flow was calculated from the concentration-time curves. Flow was varied between 2.5 and 10.0 l/min and a significant correlation was found between the MRI estimate and true flow. Volume of distribution between injection and detection site was reliably estimated. This study demonstrates rapid 2-D imaging of a paramagnetic contrast bolus in a realistic flow phantom. Reliable estimates of flow and volume are obtained.

Contrast Media↗
PubMed2004

A turbulence model for pulsatile arterial flows.

Difficulties in predicting the behavior of some high Reynolds number flows in the circulatory system stem in part from the severe requirements placed on the turbulence model chosen to close the time-averaged equations of fluid motion. In particular, the successful turbulence model is required to (a) correctly capture the "nonequilibrium" effects wrought by the interactions of the organized mean-flow unsteadiness with the random turbulence, (b) correctly reproduce the effects of the laminar-turbulent transitional behavior that occurs at various phases of the cardiac cycle, and (c) yield good predictions of the near-wall flow behavior in conditions where the universal logarithmic law of the wall is known to be not valid. These requirements are not immediately met by standard models of turbulence that have been developed largely with reference to data from steady, fully turbulent flows in approximate local equilibrium. The purpose of this paper is to report on the development of a turbulence model suited for use in arterial flows. The model is of the two-equation eddy-viscosity variety with dependent variables that are zero-valued at a solid wall and vary linearly with distance from it. The effects of transition are introduced by coupling this model to the local value of the intermittency and obtaining the latter from the solution of a modeled transport equation. Comparisons with measurements obtained in oscillatory transitional flows in circular tubes show that the model produces substantial improvements over existing closures. Further pulsatile-flow predictions, driven by a mean-flow wave form obtained in a diseased human carotid artery, indicate that the intermittency-modified model yields much reduced levels of wall shear stress compared to the original, unmodified model. This result, which is attributed to the rapid growth in the thickness of the viscous sublayer arising from the severe acceleration of systole, argues in favor of the use of the model for the prediction of arterial flows.

Animals↗
PubMed2005

Endothelial KLF2 links local arterial shear stress levels to the expression of vascular tone-regulating genes.

Lung Krüppel-like factor (LKLF/KLF2) is an endothelial transcription factor that is crucially involved in murine vasculogenesis and is specifically regulated by flow in vitro. We now show a relation to local flow variations in the adult human vasculature: decreased LKLF expression was noted at the aorta bifurcations to the iliac and carotid arteries, coinciding with neointima formation. The direct involvement of shear stress in the in vivo expression of LKLF was determined independently by in situ hybridization and laser microbeam microdissection/reverse transcriptase-polymerase chain reaction in a murine carotid artery collar model, in which a 4- to 30-fold induction of LKLF occurred at the high-shear sites. Dissection of the biomechanics of LKLF regulation in vitro demonstrated that steady flow and pulsatile flow induced basal LKLF expression 15- and 36-fold at shear stresses greater than approximately 5 dyne/cm2, whereas cyclic stretch had no effect. Prolonged LKLF induction in the absence of flow changed the expression of angiotensin-converting enzyme, endothelin-1, adrenomedullin, and endothelial nitric oxide synthase to levels similar to those observed under prolonged flow. LKLF repression by siRNA suppressed the flow response of endothelin-1, adrenomedullin, and endothelial nitric oxide synthase (P < 0.05). Thus, we demonstrate that endothelial LKLF is regulated by flow in vivo and is a transcriptional regulator of several endothelial genes that control vascular tone in response to flow.

Adrenomedullin↗
PubMed1997

An investigation of the relationship between ultrasound echo enhancement and Doppler frequency shift using a pulsatile arterial flow phantom.

RATIONALE AND OBJECTIVES: Based on the echo-enhancing effect of microbubbles, various agents have been developed to improve the diagnostic confidence in patients with inadequate Doppler signals. In the clinical trials of the echo enhancer Levovist, there were a few isolated cases in which the maximum flow velocities of the enhanced Doppler spectra appeared to higher than the velocities in the nonenhanced baseline spectra. This raised the concern that echo enhancement could give a false indication of maximum flow velocity. This study investigated whether a systematic association between echo enhancement and velocity shift exists. METHODS: A pulsatile flow phantom that simulated the elasticity of blood vessels and the acoustic attenuation of extravascular tissue was used to compare enhanced with unenhanced Doppler spectra under accurately reproducible flow conditions. The experiments were carried out with varied sound attenuation and evaluated with dedicated spectral analysis software that included a special averaging tool. RESULTS: Levovist enhanced the Doppler signal by 16 to 31 dB, and the enhanced and unenhanced power spectra presented identical distribution of spectral power density under all flow conditions. CONCLUSIONS: The measurements gave no evidence that echo enhancement with Levovist falsifies the Doppler measurement of flow velocity.

Blood Flow Velocity↗
PubMed2004

Radial distributions of temperature pressure and velocities for pulsatile blood flow in an axisymmetrical stiff tube.

Using perturbation theory with the assumption that the pulsatile blood flow in an axisymmetrical stiff tube is the first-order term to solve the linear equations of continuity, motion and heat conduction, the equations of the pulsatile flow, including temperature, are derived, and the instantaneous radial distribution of temperature, pressure and velocities for one frequency component are obtained. Using the published geometrical and physiological parameters of a large artery, a numerical analysis of the distribution relationship between the axial velocity and temperature is carried out. The primary studies show that the amplitude of temperature fluctuation in the tube is inversely proportional to the pulsatile frequency, the temperature and velocities gradients are mainly restricted in the near-wall layers with the increase of pulsatile frequency, and there is a close similarity of the radial pulsating distribution between temperature and axial velocity, which indicates that the blood flux in the artery as well as the motion function of heart can be indirectly described by the measurement of temperature fluctuation.

Animals↗
PubMed2006

Stress analysis in a layered aortic arch model under pulsatile blood flow.

BACKGROUND: Many cardiovascular diseases, such as aortic dissection, frequently occur on the aortic arch and fluid-structure interactions play an important role in the cardiovascular system. Mechanical stress is crucial in the functioning of the cardiovascular system; therefore, stress analysis is a useful tool for understanding vascular pathophysiology. The present study is concerned with the stress distribution in a layered aortic arch model with interaction between pulsatile flow and the wall of the blood vessel. METHODS: A three-dimensional (3D) layered aortic arch model was constructed based on the aortic wall structure and arch shape. The complex mechanical interaction between pulsatile blood flow and wall dynamics in the aortic arch model was simulated by means of computational loose coupling fluid-structure interaction analyses. RESULTS: The results showed the variations of mechanical stress along the outer wall of the arch during the cardiac cycle. Variations of circumferential stress are very similar to variations of pressure. Composite stress in the aortic wall plane is high at the ascending portion of the arch and along the top of the arch, and is higher in the media than in the intima and adventitia across the wall thickness. CONCLUSION: Our analysis indicates that circumferential stress in the aortic wall is directly associated with blood pressure, supporting the clinical importance of blood pressure control. High stress in the aortic wall could be a risk factor in aortic dissections. Our numerical layered aortic model may prove useful for biomechanical analyses and for studying the pathogeneses of aortic dissection.

Aorta, Thoracic↗
PubMed1987

Effects of droperidol on peripheral vasculature: use of cardiopulmonary bypass as a study model.

The effects of droperidol on the systemic vascular resistance (SVR) and the venous capacitance were studied during cardiopulmonary bypass (CPB) in 24 patients. CPB was performed with either pulsatile or non-pulsatile flow. During non-pulsatile flow, droperidol (0.15 mg X kg-1 and 0.30 mg X kg-1) decreased SVR and increased venous capacitance. These values were significantly different after the 2nd and the 7th min, respectively. During pulsatile flow, the initial SVR was lower. The decremental effect of 0.30 mg X kg-1 droperidol on SVR was proportional to the preinjection level of SVR (r = 0.64). The increase in venous capacitance related to droperidol was independent of the dose and of the type of flow in all patients. It can be concluded that the vasodilating action of droperidol during CPB on the arterial bed is transient, independent of dose, and related to the preinjection level of SVR. The effect of droperidol on venous capacitance is not as rapid but has a longer duration.

Blood Vessels↗
PubMed1998

Mass transfer efficiency of a commercial hollow fibre oxygenator during six-hour in vitro perfusion with steady and with pulsatile blood flow.

Detailed data about the behaviour of commercial membrane oxygenators with pulsatile blood flow are rarely available. This work deals with an experimental evaluation of the effects induced on gas transfer efficiency by pulsatile perfusion of a hollow fibre oxygenator (Monolyth Sorin Biomedica). The oxygenator was subjected to two in vitro trials both carried out with identical experimental protocols except for the flow type, steady and pulsatile. A roller pump with pulsatile module (Stöckert Instrument) was used to generate both flow types. Three different mean blood flow rates (3.2, 4.0 and 4.8 L/min) were tested. The experiments lasting six hours were carried out using bovine blood with inlet conditions according to AAMI standard requirements. Blood samples were withdrawn every hour and the calculated gas transfer obtained in the two sessions were compared. The device proved to be well-designed for steady flow and to be liable to similar gas transfer performance when used in pulsatile conditions. Furthermore, the use of pulsatile flow rather than steady flow provided more consistent conditions and resulted in a higher eventual oxygen transfer efficiency (final mean difference = 6.2%, p < 0.05), proving to be able to avoid any performance decays.

Animals↗
PubMedDate not supplied

A numerical investigation of the dependence of NMR signal from pulsatile blood flow in CINE pulse sequences.

The Bloch equations have been solved using numerical techniques for a uniform fluid undergoing periodic pulsatile flow in an NMR imaging experiment. The magnetization and NMR signal have been calculated for experimental parameters appropriate for a CINE sequence (TR = 40 ms, (TE = 14 ms) applied to the study of pulsatile aortic or other arterial flows. The flow velocity profile is obtained by Fourier superposition of different harmonics and it is shown that the steady-state NMR signal has reduced high-frequency components. There is also a time delay between peak signal intensity and flow because the backflow effects that can be as much as 100 ms. The apparent pulsatility depends on the NMR sequence parameters. Some limitations of the phase contrast flow-imaging method are also discussed for nonuniform flow.

Blood Flow Velocity↗
PubMed1981

Pulsatile venous flow in extracorporeal circulation.

Effects of pulsatile venous flow upon the microcirculation were investigated in conditions with different venous pressures by using regional perfusion in dog's hind legs. In animals with venous pressure of -18 cmH2O (Collapsed stage), venous pulsation brought about a significant increase in mean oxygen consumption ratio and suppressed a rise of mean resistance ratio significantly. In animals with venous pressure of +2 cmH2O (normal venous pressure stage), the venous pulsation was effective in a rise of mean oxygen consumption ratio but was not effective in suppression of mean resistance ratio. In animals with venous pressure of +10 cmH2O (congestive stage), no effect of venous pulsation was recognized. We suppose that the intermittent elevation of venous pressure by venous pulsation is effective for opening some capillaries in animals with venous pressure below +2 cmH2O.

Animals↗
PubMed2001

[Pulsatile rotary pumps with low hemolysis].

As is well known, a pulsatile flow is important in assisted-circulation but it is difficult to produce a pulsatile flow with rotary pump, because excessive hemolysis will be generated. The authors have found that the turbulent shear is the main factor for red cell damage and therefore the key point of pulsatile rotary pumps is to reduce the turbulence by producing a pulsatile flow. In the authors' pulsatile axial pump, the pulsatile flow is obtained by axial reciprocation of constant rotating impeller; the rotation and reciprocation of the impeller are driven separately by a DC motor and a pneumatic device. Though a physiological pulsatile flow could be achieved and turbulence would not increase remarkably because the impeller rotates constantly, a second driver except a DC motor is nevertheless necessary, thus the system will become complicated. In the authors' pulsatile radial pump, a pulsatile flow is achieved by changing the rotating speed of the impeller periodically. Turbulence is minimized by a special design of twisted vanes which enable the blood flow to change its direction rather than its dimension during periodic change of rotating speed. Hemolysis tests demonstrated that the index of hemolysis(IH) of the author's pulsatile radial pump is 0.020, with is slightly more than that of the author's nonpulsatile radial pump(IH = 0.015). Animal experiments indicated that the pulsatile radial pump can assist the circulation of calves for several months without harm to blood elements and organ functions of the recipients.

Animals↗
PubMed2001

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

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

Anastomosis, Surgical↗