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PubMed1983

Stenosis severity effects for unbalanced simple-pulsatile bifurcation flow.

A numerical finite-difference analysis is made of a plane simple-pulsatile flow past a symmetrical bifurcation which contains an asymmetrical smooth-contoured stenosis in the trunk. In essence, such a situation could represent a stenosed common carotid artery immediately upstream from the carotid junction. The flow is unbalanced; two-thirds of it exits or enters through the lower branch. The effect on various flow parameters of the stenosis itself and on changes in its severity is investigated by comparing the results for a severe stenosis, a mild stenosis, and no stenosis. The simple-pulsatile forcing function is specified in terms of an oscillatory and a steady Karman number. To obtain a significant amount of backflow, the oscillatory trunk Karman number is taken as 1000 compared to the steady value of 250. The frequency of oscillation is stipulated by a trunk Stokes number of 10 pi. The numerical procedures utilize the vorticity-transport version of the Navier-Stokes governing equations. A non-orthogonal coordinate transform allows the calculations to be made in a rectangular grid where the central difference expressions are easily applied. The results are presented in terms of both kinematic and kinetic parameters. The variation in the basic kinematic variables of stream function and vorticity is shown by temporal sequences of contour plots at times of peak flow and during the flow reversal stages as well as by several velocity vector plots. Kinetic results are given in terms of the temporal variation in shear stresses along boundaries. The peak shears are found to occur at the zenith of the stenosis at times of peak flow: the value for the severe stenosis is twice as large as that for the mild stenosis. The midline pressure distribution in the trunk and the centerline pressure distributions in the branches are also included.

Carotid Arteries↗
PubMed1995

Mechanics of pulsatile transpyloric flow in the pig.

1. In eight conscious pigs equipped with gastric and duodenal cannulae, the relationship of transpyloric flow to gastro-duodenal motor events was evaluated during gastric emptying of 1000 ml of saline. Rates of liquid gastric emptying were correlated with pressures at the antrum, pylorus and duodenum, recorded by a sleeve sensor and multiple perfused side-holes. Transpyloric flow was recorded concurrently by continuous collection and weighing of the duodenal effluent. 2. In three pigs the above measurements were repeated during concurrent videofluoroscopy of gastric emptying after adding 100 ml of liquid barium to the gastric instillate. 3. The mean volume of saline emptied in 30 min was 627 +/- 51.2 ml. Pulsatile flow accounted for 71% of total emptying. Pulses had a mean flow rate of 3.9 +/- 0.44 ml s-1. Most flow pulses (59%) occurred during the first 5 min of emptying. 4. Distinctive, low-amplitude (4.8 +/- 0.33 mmHg), relatively long-lasting (15.8 +/- 0.46 s) antral pressure waves were associated with 58% of flow pulses. In all antral pressure recording points, the first and longest duration component of these pressure waves had an identical timing, amplitude and waveform consistent with pressurization of the entire antrum-gastric cavity. 5. Videofluoroscopy and concurrent manometry showed that these antral common cavity pressure waves were associated with non-lumen-occlusive contractions of the gastric wall, initially observed at the corpus which propagated down to the pylorus; 93% of these contractions became lumen occlusive in the terminal antrum and pylorus when pressure waves of a unique pattern for each recording point were recorded at this level. 6. The onset of 68% of the flow pulses which accounted for 62% of pulsatile emptying occurred in the interval (mean 7.9 +/- 0.65 s) between the onset of the common cavity wave and the onset of localized, lumen-occlusive distal antral-pyloric pressure waves. 7. These findings indicate that in the pig, pulsatile emptying of non-nutrient liquids into the duodenum occurs predominantly during the non-lumen-occlusive stage of a propagated gastric contraction, which is recognisable as a common cavity pressure wave. This is a previously inadequately recognized pattern of gastric pumping.

Animals↗
PubMed2001

In situ hemodynamics of perforating veins in chronic venous insufficiency.

PURPOSE: The prevalence of incompetent perforators increases linearly with the clinical severity of chronic venous insufficiency (CVI) and the presence of deep vein incompetence. Putative transmission of deep vein pressure to skin may cause dermal hypoxia and ulceration. Despite extensive prospective interest in the contribution of perforators toward CVI, their hemodynamic role remains controversial. The aim of this prospective study was to determine the in situ hemodynamic performance of incompetent perforating veins across the clinical spectrum of CVI, by means of duplex ultrasonography. METHODS: A total of 265 perforating veins of 90 legs that had clinical signs and symptoms consistent with CVI in 67 patients referred consecutively to the blood flow laboratory were studied. The clinical distribution of the examined limbs was CEAP(0), 10 limbs; CEAP(1-2), 39 limbs; CEAP(3-4), 21 limbs; and CEAP(5-6), 20 limbs. With the use of gated-Doppler ultrasonography on real-time B-mode imaging, the flow velocity waveforms were obtained from the lumen of perforators on release of manual distal leg compression in the sitting position and analyzed for peak and mean velocities, time to peak velocity, volume flow, venous volume displaced outward, and flow pulsatility. The diameter and duration of outward flow (abnormal reflux > 0.5 seconds) were also measured. RESULTS: Incompetent perforators had bigger diameters, higher peak and mean velocities and volume flow, longer time to peak velocity, and bigger venous volume displaced outward (VV(outward)) than competent perforators (all, P <.0001). The diameter of incompetent perforators did not change significantly with CEAP class (all, P >.1). Incompetent thigh and lower-third calf perforators had a significantly bigger diameter than perforators in the upper and middle calf combined (both, P <.05), in incompetent perforators: reflux duration was unaffected by CEAP class or site (P >.3); peak velocity was higher in those in CEAP(3-4) than those in CEAP(1-2) (P =.024); mean velocity in those in CEAP(3-6) during the first second of reflux was twice that of those in CEAP(1-2) (P <.0001); both higher volume flow and VV(outward) were found in the thigh perforators than those in the upper and middle calf thirds (P <.03); CEAP(3-6) volume flow and VV(outward), both in the first second, were twice that in those in CEAP(1-2) (P <.002); flow pulsatility in those in CEAP(5-6) was lower than in those in CEAP(1-2) (P =.014); in deep vein incompetence, higher peak velocity, volume flow, VV(outward), and diameter occurred than in its absence (P <.01). CEAP designation correlated significantly with mean velocity and flow pulsatility, both in the first second (r = 0.3, P <.01). The flow direction pattern in perforator incompetence was uniform across the CVI spectrum: inward on distal manual limb compression, and outward on its release; competent perforators had a smaller percentage of outward flow on limb compression (P <.01). CONCLUSION: In addition to an increase in diameter, perforator incompetence is characterized by significantly higher mean and peak flow velocities, volume flow, and venous volume displaced outward, and a lower flow pulsatility. Differences in early reflux enable a better hemodynamic stratification of incompetent perforators in CVI classes. In the presence of deep reflux, incompetent perforators sustain further hemodynamic impairment. In situ hemodynamics enable quantification of the function of perforators and can be used in the identification of the clinically relevant perforators and the impact of surgery.

Adolescent↗
PubMed1992

Simulation of Doppler ultrasound signals for a laminar, pulsatile, nonuniform flow.

A simulation for Doppler ultrasound quadrature signals from pulsatile, nonuniform flow is presented. It is an extension of an earlier simulation presented by Jones and Giddens (1990a) which was valid for laminar, uniform, steady flow and which included the stochastic characteristics introduced by scattering particles which enter and leave the sample volume at random times. Fourier transform and autoregressive spectral analysis techniques are used to compare the simulated signals to Doppler signals collected from an in vitro flow setup. Power spectra, Doppler frequency estimates and standard deviations of these estimates serve as standards of comparison. Results show that the simulation model generates realistic quadrature signals. The study improves the understanding of the physics of the Doppler process and shows that it can be modeled for complex flow conditions. The input parameters of the simulation are the Doppler instrument parameters and flow characteristics. This allows the simulation to be used for transducer design as well as in the study of the applicability of signal analysis techniques to Doppler ultrasound.

Blood Flow Velocity↗
PubMed1993

The effects of curvature on fluid flow fields in pulmonary artery models: flow visualization studies.

In vitro pulsatile flow visualization studies were conducted to assess the effects of varying radii of curvature of the right ventricular outflow tract (RVOT) and main pulmonary artery (MPA) on the flow fields in the main, right, and left pulmonary arteries of a one month lamb pulmonary artery model. Three glass flow-through models were studied; one with no curvature, one with the correct anatomic curvature, and one with an overaccentuated curvature on the RVOT and MPA. All other geometric parameters were held constant. Pulsatile flow visualization studies were conducted at nine flow conditions; heart rates of 70, 100, and 140 bpm, and cardiac outputs of 1.5, 2.5 and 3.5 l/min with corresponding mean pulmonary pressures of 10, 20, and 30 mmHg. Changes were observed in the pulmonary flow fields as the curvature of the outflow tract, heart rate and mean pulmonary pressure were varied. An increase in vessel curvature led to an increase in the overall radial nature of the flow field as well as flow separation regions which formed faster, originated further downstream, and occupied more of the vessel area. At higher heart rates, the maximum size of the separation regions decreased, while flow separation regions appeared earlier in the cardiac cycle and grew more quickly. Heart rate also affected the initiation of flow reversal; flow reversal occurred later in the cardiac cycle at lower heart rates. Both heart rate and mean pulmonary pressure influenced the stability of the pulmonary flow field and the appearance of coherent structures. In addition, an increase in mean pulmonary pressure increased the magnitude of reverse flow.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1995

Portal vein thrombosis in patients with cirrhosis: does sonographic detection of intrathrombus flow allow differentiation of benign and malignant thrombus?

OBJECTIVE: The objective of our study was to determine if the detection by Doppler sonography of blood flow in portal vein thrombi occurring in patients with cirrhosis could be used to distinguish benign from malignant portal vein thrombi. SUBJECTS AND METHODS: Color and duplex Doppler sonographic examinations were performed in 47 patients with proven cirrhosis and portal vein thrombi. The examinations were directed at the detection of continuous or pulsatile flow within the portal vein thrombi. The nature of the portal vein thrombi was proven histologically in 27 patients and by CT findings and clinical history in 20 patients. The frequency, type, and direction of portal vein thrombus flow was evaluated to determine if there was any correlation with the benign or malignant nature of the portal vein thrombi. RESULTS: Of the 47 patients, 26 had malignant portal vein thrombi and 21 had benign portal vein thrombi. Blood flow was detected in 22 of the malignant and in 15 of the benign portal vein thrombi. The blood flow was pulsatile in 16 malignant and three benign portal vein thrombi and continuous in six malignant and 12 benign portal vein thrombi. The direction of the pulsatile flow in the malignant portal vein thrombi was predominantly (13/16) hepatofugal. All continuous flow in both benign and malignant portal vein thrombi was hepatopetal. The detection of pulsatile flow in portal vein thrombi yielded a 62% sensitivity and 95% specificity for the diagnosis of malignant portal vein thrombus. CONCLUSION: The detection by Doppler sonography of pulsatile flow in portal vein thrombi occurring in patients with cirrhosis is a moderately sensitive but highly specific sign for the diagnosis of malignant portal vein thrombus. However, continuous flow can be detected in benign and malignant portal vein thrombus and is thus not useful in differentiating between the two.

Adult↗
PubMed2007

A hybrid one-dimensional/Womersley model of pulsatile blood flow in the entire coronary arterial tree.

Using a frequency-domain Womersley-type model, we previously simulated pulsatile blood flow throughout the coronary arterial tree. Although this model represents a good approximation for the smaller vessels, it does not take into account the nonlinear convective energy losses in larger vessels. Here, using Womersley's theory, we present a hybrid model that considers the nonlinear effects for the larger epicardial arteries while simulating the distal vessels (down to the 1st capillary segments) with the use of Womersley's Theory. The main trunk and primary branches were discretized and modeled with one-dimensional Navier-Stokes equations, while the smaller-diameter vessels were treated as Womersley-type vessels. Energy losses associated with vessel bifurcations were incorporated in the present analysis. The formulation enables prediction of impedance and pressure and pulsatile flow distribution throughout the entire coronary arterial tree down to the first capillary segments in the arrested, vasodilated state. We found that the nonlinear convective term is negligible and the loss of energy at a bifurcation is small in the larger epicardial vessels of an arrested heart. Furthermore, we found that the flow waves along the trunk or at the primary branches tend to scale (normalized with respect to their mean values) to a single curve, except for a small phase angle difference. Finally, the model predictions for the inlet pressure and flow waves are in excellent agreement with previously published experimental results. This hybrid one-dimensional/Womersley model is an efficient approach that captures the essence of the hemodynamics of a complex large-scale vascular network. The present model has numerous applications to understanding the dynamics of coronary circulation.

Animals↗
PubMedDate not supplied

Delineation of simulated vascular stenosis with Gd-DTPA-enhanced 3D gradient echo MR angiography: an experimental study.

PURPOSE: The purpose of this experimental study was to evaluate the influence of contrast material concentration and flow velocity on pulsatile flow in Gd-DTPA-enhanced 3D gradient echo MR angiographic sequence. METHOD: In vivo flow experiments were performed in Plexiglas phantoms with artificial stenosis (50% stenotic ratio and 20 mm stenotic length) attached to a cardiac pump that generated physiological pulsatile flow similar to that of the bloodstream in a closed circuit. We used a steady-state gradient echo sequence with different TEs (6, 3, and 1.4 ms). A TR of 15 ms was used for all parameters. The concentration of Gd-DTPA varied from 0 to 2.0 mmol/L and flow velocities from 25 to 80 cm/s. We measured the degree of stenosis and length of stenosis in comparison with the actual values. RESULTS: The degree and length of stenosis on 3D gradient echo MR angiographic images were markedly influenced by the velocity of the flow and concentration of Gd-DTPA. The degree of stenosis was overestimated when the flow was fast or when the concentration of Gd-DTPA was low. When the concentration of Gd-DTPA was low, stenosis was elongated. These effects were less prominent on short TE (1.4 ms) sequence. CONCLUSION: The stenotic lesions were markedly overestimated on MR angiographic images obtained with Gd-DTPA-enhanced fast 3D gradient echo sequence. Spin dephasing can be compensated for almost entirely by a high concentration of Gd-DTPA and/or a short TE sequence.

Arterial Occlusive Diseases↗
PubMed1988

Cerebral hemodynamics in infants undergoing extracorporeal membrane oxygenation: further observations.

Intracranial Doppler ultrasonographic examinations were performed on 64 infants treated with extracorporeal membrane oxygenation (ECMO). Serial studies were performed on the anterior cerebral artery in 55 infants before and during ECMO bypass, and on the middle cerebral arteries (MCAs) and internal carotid arteries (ICAs) on an additional nine infants. The onset of ECMO was associated with changes in character of pulsatile flow, direction of flow, and mean blood-flow velocity. Pulsatility decreased in all patients, and mean blood-flow velocity increased in 73% of patients (mean change from baseline, 87%). Despite retrograde flow in the right ICA in five of nine infants, antegrade flow to the right MCA was preserved in all cases. We found no correlation between alterations in mean blood-flow velocity and overall mortality, frequency of intracranial hemorrhage, and neuro-developmental outcome. These data suggest that wide variations in cerebral blood flow occur with ECMO therapy, and that these changes appear to be well tolerated.

Blood Flow Velocity↗
PubMed2004

In vitro assessment of a continuous cardiac output catheter system.

Continuous measurement of cardiac output (CCO) is useful in assessing the cardiovascular status of patients during cardiac surgery and in intensive care. Recently, a CCO system (truCCOMS, Aortech, UK), capable of detecting rapid changes in cardiac output (CO) was introduced. The method is based on the energy required to maintain an integral heat-transfer device at constant temperature above the ambient value. The aim of this study was to assess the performance of this CCO system in vitro under in steady as well as pulsatile flow conditions representative of those in the pulmonary artery. In order to determine the sensitivity of the system to changes in vessel cross-sectional area and therefore local flow velocity, the catheter was deployed in a linear-tapered tube. Steady and pulsatile flows were generated, and the electrical power at various locations along the tapered tube was recorded. The results show significant differences in the performance under the two different flow conditions. In steady flow, the CO was highly dependent on the local velocity whereas in pulsatile flow, CO varied much less with local velocity. The sensitivity expressed as a percentage increase in CO per 100% increase in velocity at a CO of 5 l min(-1) was 87% in steady flow and 24% in pulsatile flow. Experiments carried out with three fluids with different viscosity show that the errors in determining CO in the tapered tube were also dependent on the Reynolds number and flow regime. The mean errors ranged from about 50% at 2 l min(-1) to less than 10% at 8 l min(-1). The correlation between the predicted and actual CO was generally good. In conclusion, the pulmonary artery catheter is not recommended in situations where blood flow is expected to be steady or of low pulsatility. It may, however, be suitable under normal pulsatile flow conditions in the pulmonary artery.

Cardiac Catheterization↗
PubMed1997

Development of an in vitro model to study the response of saphenous vein endothelium to pulsatile arterial flow and circumferential deformation.

OBJECTIVES: To develop an in vitro model of human saphenous vein bypass to facilitate study of the early adaptive responses of venous endothelium to arterial flow conditions. DESIGN MATERIAL AND METHODS: Segments of human saphenous vein (with or without external polytetrafluoroethylene (PTFE) stents to limit circumferential and radial deformation) were mounted in a bypass circuit and subjected to pulsatile flow with oxygenated Krebs solution to simulate arterial or venous flow conditions for a period of 90 min. The viability of the vein was assessed by the tissue ATP concentration and vasomotor responses to phenylephrine, sodium nitroprusside and bradykinin (endothelium-dependent). Immunohistochemistry was used to assess both endothelial preservation (CD31) and the expression of proteins involved in leukocyte adhesion: E-selectin, P-selectin and ICAM-1. Freshly excised veins were used as controls. RESULTS: The concentration of ATP was 320 +/- 11 nmol/g in freshly excised vein (n = 8) and following exposure to the arterial flow circuit increased to 566 +/- 60 nmol/g (n = 8, paired t-test, p = 0.003) in unstented veins and to 421 +/- 49 nmol/g (n = 8, paired t-test, p = 0.002) in externally stented veins (with PTFE). Both endothelium-dependent and sodium nitroprusside-induced vasodilatation responses were preserved after veins were exposed to the arterial flow circuit, but the sensitivity to phenylephrine was increased: EC50 decreasing from 9 microM, p = 0.008. There was a 5-10% decrease in staining area for CD31 after veins, stented or unstented, were exposed to the arterial flow circuit. However, after exposure to the arterial flow circuit, the staining area ratio for ICAM-1/CD31, which remained unchanged in externally stented veins, increased two-fold in unstented veins, p > 0.01: there were no changes in the staining area ratio P-selectin/CD31 and no staining for E-selectin was observed. CONCLUSION: Vasomotor responses and tissue ATP concentration indicate that the viability of saphenous vein can be maintained for up to 90 min in an ex vivo flow circuit and the CD31 staining indicated endothelial preservation. This opens up the possibility of investigating the early changes in saphenous vein endothelium following exposure to arterial pressure, as at bypass surgery. First results suggest that there is rapid upregulation of the leukocyte adhesion molecule ICAM-1, which can be prevented by limiting the circumferential deformation of the vein with an external PTFE stent.

Adaptation, Physiological↗
PubMed2001

Analytical solution for pulsatile axial flow velocity waveforms in curved elastic tubes.

An analytical solution for pulsatile axial flow velocity waveforms in curved elastic tubes is presented. The result is obtained by exact solution of linearized Navier-Stokes and tube motion equations in a torroidal coordinate system. Fourier analysis is used to divide the flow into constant and oscillatory components which are separately considered. The solution is used to investigate the effects of curvature on volumetric axial velocity flow waveforms, as would be measured by Doppler ultrasound techniques. In typical human arteries, the greatest effects of curvature on the volumetric axial flow are exerted on the constant component and at low values of the frequency parameter for the oscillatory components. Here, the magnitude and phase angle of oscillatory flow in the curved tube, relative to that in the straight tube, differ by maximum values of 1.2% and 0.15 rad, respectively. However, constant flow may vary by as much as 60% at high Dean numbers. The solution is presented in a form similar to Womersley's solution for the straight elastic tube and may, thus, be incorporated into a transmission-line analog model. These models are frequently used to investigate axial flow velocity variations in mamillian circulatory systems and this work offers a tool which may extend these models to incorporate the effects of curvature.

Algorithms↗
PubMed1993

Effects of dopamine agonists and antagonists on pulsatile blood flow of ocular hypertensive rabbits.

It has been reported that some dopamine antagonists can suppress the intraocular pressure and can increase the blood flow in the retina and choroid. Therefore, several dopamine antagonists and agonists were studied to determine if they can increase the ocular pulsatile blood flow in ocular hypertensive rabbits with the intraocular pressure raised artificially to 40 mm Hg. It was found that numerous dopamine antagonists including loxapine, moperone, domperidone, haloperidol and metoclopramide increased pulsatile blood flow for 49-110%, 95-155%, 72-86%, 60-114%, and 39-139%, respectively. Floropipamide reduced the ocular pulsatile blood flow for 18% at 90 min and 10% at 120 min. Chlofluperol produced biphasic action on pulsatile blood flow by significantly reducing it initially at 60 min (-49%) and then markedly increasing it at 180 min (91%). In case of dopamine agonists, neither dopamine nor bromocriptine affected the pulsatile blood flow significantly. These results indicate that some of dopamine antagonists could be used to lower the intraocular pressure and to increase the ocular pulsatile blood flow as well.

Animals↗
PubMed2002

Detection of pulsatile blood flow cycle in frog microvessels by image velocimetry.

The detection of pulsatile blood flow velocity through one section of a curved branching frog mesenteric microvessel during a flow cycle, by analysis of a sequence of videomicroscopic images recorded at a frame rate 25 frames s-1, is presented. From these data, 64 sequential digitized frames of 128 x 128 pixels and 256 grey level were selected. By processing sequential pairs of frames by image velocimetry, the corresponding displacement vector was calculated. Dividing this by the frame rate gave the vector velocity. The same procedure was repeated for all frames, and the corresponding maximum (0.36-0.38 mm s-1), minimum (0.0-0.025 mm s-1) and other velocity values were obtained and plotted. The preliminary data analysis showed that the separation between two velocity maxima was about 20 video frames, which corresponded to one cardiac cycle of time interval 0.8 s.

Animals↗
PubMed1989

[The necessary advantage of measuring the pulsatile arterial flow of the limbs in patients with arterial disease].

Proper determination of vascular haemodynamics requires measurement of flow and pressure. The objective of this study is to provide methods of measurement of the arterial flow, which may currently be performed via an external approach. The techniques in question include non-invasive electromagnetic flowmetry (NMF) and flowmetry by NMR. NMF uses external magnets, the signal is collected by common cutaneous electrodes; the equipment is simple and may be used in a cardio-angeiology office. It main advantage lies in the screening of arterial diseases (very reproductable and sensitive), monitoring of the treatment (unrelated to the operator), study of hardened arteries (diabetes). Flowmetry by NMR requires a more sophisticated and costly equipment; it permits staged measurements, as well as a scan permitting measurements in one single artery; it is mostly used in specialized centres. Arterial lesions may be defined as not yet significant when only the blood pressure is considered, while the pulsatile flow is already altered; transluminal angioplasties performed in these circumstances, permit to restore the clinical picture as well as increasing twofold the initial flow.

Arterial Occlusive Diseases↗
PubMed1986

The hemodynamic and embolizing forces acting on thrombi--II. The effect of pulsatile blood flow.

A previous analysis (Basmadjian, J. Biomechanics 17, 287-298, 1984) of the embolizing forces acting on thrombi in steady Poiseuille flow has been extended to pulsatile blood flow conditions in the major blood vessels. We show that for incipient and small compact thrombi up to 0.1 mm height, the maximum embolizing stresses can be calculated from the corresponding 'quasi-steady' viscous drag forces and measured maximum wall shear. Their magnitude is from 5 to 30 times (tau w)Max, the maximum wall shear stress during the cardiac cycle in the absence of thrombi. For larger thrombi, inertial and 'history' effects have to be taken into account, leading to embolizing stresses in excess of 100 Pa (1000 dyn cm-2).

Blood Circulation↗