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PubMed2005

Systolodiastolic variations of blood flow during central retinal vein occlusion: exploration by dynamic angiography.

BACKGROUND/AIM: In patients with acute central retinal vein occlusion (CRVO), dynamic angiography may reveal the presence of pulsatile flow (termed here pulsatile venular outflow, PVO) within first order veins (that is, the large veins). The main goal of this study was to investigate the mechanism underlying PVO. METHODS: 10 patients with CRVO and PVO were included. Quantitative and qualitative analysis of venous flow on dynamic angiograms allowed the correlation, temporally, of second and first order vein flow on the one hand, and venous flow and systolic cycle on the other. RESULTS: Analysis of the time-velocity curve showed that (1) the onset of arterial systole preceded the onset of PVO by less than 0.08 seconds (n = 5); (2) PVO onset was simultaneous to the time of onset of minimal flow (Vmin) in first order veins (n = 10); (3) the time of onset of maximal flow (Vmax) in first order veins occurred 0.20-0.44 seconds after the onset of PVO (n = 6). CONCLUSIONS: During CRVO with severe reduction in blood flow, the presence of PVO is the result of the existence of a distinct haemodynamic regimen in first and second order veins. These data support the hypothesis that second order veins flow is synchronous with the arterial flow, while the delayed peak flow in first order veins may reflect the consequences of the delayed IOP curve and/or of intermittent venous compression.

Acute Disease↗
PubMed1997

In Vitro Validation of Rapid MR Measurement of Wave Velocity

A one-dimensional time-of-flight MR sequence, having a total acquisition time of approximately 60 ms, has been employed to determine flow-wave propagation velocities for pulsatile flow in compliant latex tubes. The results were compared with those of two independent methods and were found to be in good agreement. An extension of the same MR method was used to test the validity of the "water-hammer" relationship as a means to assess pulse pressure. Very good agreement was found with direct manometric determinations of pulse pressure.

Journal Article↗
PubMed2004

Arterial stiffness and function in end-stage renal disease.

Cardiovascular disease is a major cause of mortality in patients with end-stage renal disease, with damage to arteries as a major contributing factor. Arterial stiffness is a factor associated with high systolic and pulse pressure in these patients and is a strong independent factor associated with morbidity and mortality. Arterial stiffness is one of the principal factors opposing left ventricular ejection. The appropriate term to define the arterial factor(s) opposing left ventricular ejection is aortic input impedance. Aortic input impedance depends on TPR, arterial distensibility, and wave reflections. Distensibility defines the capacitive properties of arterial stiffness, whose role it is to dampen pressure and flow oscillations and to transform pulsatile flow and pressure in arteries into a steady flow and pressure in peripheral tissues. Stiffness is the reciprocal value of distensibility. These parameters are blood pressure dependent; arteries become stiffer at high pressure. While distensibility provides information about the elasticity of the artery as a hollow structure, the elastic incremental modulus characterizes the properties of the arterial wall biomaterials independent of vessel geometry. Alternatively, arterial distensibility can be evaluated by measuring pulse wave velocity, which increases with the stiffening of arteries. Arterial stiffening increases left ventricular afterload and alters the coronary perfusion. With increased pulse wave velocity, the wave reflections affects the aorta during systole, which increases systolic pressures and myocardial oxygen consumption and decreases diastolic blood pressure and coronary flow. The arterial stiffness is altered primarily in association with increased collagen content and alterations of extracellular matrix and calcification of the arterial wall. The arterial stiffening estimated by changes in aortic pulse wave velocity and intensity of wave reflections are independent predictors of survival in end-stage renal disease and in the general population. Improvement of arterial stiffening could be obtained by antihypertensive treatments as observed with calcium-channel blockers and angiotensin-converting enzyme inhibitors. Angiotensin-converting enzymes inhibitors increase AC and reduce wave reflections. It has been shown that reversibility of aortic stiffening and use of angiotensin-converting enzyme inhibitors had a favorable independent effect on survival in hypertensive patients with advanced renal disease.

Aorta↗
PubMed2005

Vessel wall damage caused by cerebral protection devices: ex vivo evaluation in porcine carotid arteries.

PURPOSE: To determine the extent of vessel wall damage caused by cerebral protection devices designed for carotid angioplasty by using ex vivo porcine carotid arteries. MATERIALS AND METHODS: The local animal experimentation committee did not require its approval for this study. With a benchtop vascular model (flow rate, 470 mL/min; dicrotic pulsatile flow, 76 pulses per minute; pressure, 115/67 mm Hg [mean pressure, 91 mm Hg]) into which 85 porcine internal carotid arteries (ICAs) were inserted, five different protection devices (Angioguard [Cordis/Johnson & Johnson, Miami, Fla], Filterwire EX [Boston Scientific, Natick, Mass], Trap [Microvena, White Bear Lake, Minn], Neuroshield [Abbott Laboratories, Redwood City, Calif], and Percusurge [Abbott Laboratories]) were evaluated. Adverse movement (1 cm up, 2 cm down, and 1 cm up again) of the activated devices (deployed filters or inflated balloons [Percusurge only]) was simulated, and the device was retrieved. For each of these steps (deployment, movement, retrieval) the amount of debris from the vessel wall in the effluent of the ICA was determined by using a 100-microm filter. The Mann-Whitney test was used to test for differences, and a correction for multiple comparisons was made. P < .05 was considered to indicate a significant difference. The authors attempted to determine whether there was a notable association between the total amount of debris captured and the classification of damage at microscopy. Carotid arteries were analyzed histologically with light and scanning electron microscopy. RESULTS: All examined protection devices caused dislodged debris, which was captured in the effluent filter. There were significant differences among the devices in terms of the total amount of debris captured in the filters (lowest amounts of debris, 4.75 mg [Angioguard] and 5.02 mg [Filterwire EX]; highest amount, 7.51 mg [Trap]; P < or = .001 for all). All devices caused histologically visible wall damage, with the degree of intimal denudation correlating with the mass of the debris. The Trap device caused the most severe intimal and subintimal wall damage. Adverse movement resulted in no increased debris dislodgment as compared with the debris dislodged during deployment and retrieval of the devices. CONCLUSION: On the basis of the data obtained, cerebral protection devices themselves have a potential influence on embolization rates by causing debris to be dislodged during carotid stent placement.

Angioplasty, Balloon↗
PubMed1978

Arterial flow in the lower leg correlated with plasma levels of two formulations of papaverine hydrochloride.

In patients with severe peripheral vascular disease (mean arterial flow of 40 ml/min), a suspension of papaverine in a soft gelatin capsule produced plasma levels almost three times higher than those following treatment with a sustained-release tablet formulation. The higher plasma levels resulted in significantly greater vasodilation with increased distal arterial flow. The onset of peak pulsatile flow with the soft gelatin form came sooner than with the sustained-release form. However the durations of vasodilation were similar with both papaverine preparations. The vasodilatory activity of papaverine appeared to be greater in the sympathectomized leg. The soft gelatin formulation of papter reconstruction of a large artery, and may be effective in sustaining a longer vasodilatory effect in patients with small vessel disease, when surgical procedures may not be applicable.

Aged↗
PubMed1993

[Newly-developed catheter for cardio-renal assist during intraaortic balloon counterpulsation].

A new catheter was developed for the cardio-renal assist during intra-aortic balloon counterpulsation. The catheter consists of both a large balloon of conventional IAB (TMP balloon) located at the distal end of the catheter and an additional small balloon 10 cm distant from the large balloon with common lumen and single shaft. Experimental study was carried out in the mock circulatory system simulating the descending aorta employing a conventional IAB catheter as a control. It was demonstrated that the flow in the mid portion between both balloons could be increased maximally by as much as 28% of that of the control under the continuous flow and 214% under the pulsatile flow. The double balloon catheter was considered to improve the renal perfusion as well as the coronary perfusion.

Assisted Circulation↗
PubMed1996

Pressure distribution near the occluders and impact forces on the outlet struts of Björk-Shiley convexo-concave valves during closing.

BACKGROUND AND AIMS OF THE STUDY: An in vitro study of the mechanics of closure of Björk-Shiley convexo-concave (BSCC) valves is presented in order to investigate the mechanics of outlet strut fracture reported in a small fraction of the implanted valves. MATERIALS AND METHODS: Four BSCC 29 mm valves instrumented with strain gages on the outlet strut legs were mounted in the mitral position of an axisymmetric flow chamber of a mock pulsatile flow loop. Measurements of the pressure field in the vicinity of the occluder, closing velocity of the occluder tip in the major orifice, and the impact force between the occluder and outlet strut at the instant of valve closure were obtained at a range of physiologic flow rates. RESULTS: The results indicated an uneven pressure distribution on the occluder associated with a tendency for the occluder to over-rotate and induce loads on the outlet struts. The impact loads on the outlet struts were asymmetric with load on one leg being larger than the other by up to 25%. These results are consistent with single leg separation preceding outlet strut fracture in most of the valve failures reported. Orientation of the valve with respect to the mitral orifice (major orifice towards the top or bottom) did not significantly affect the loads on the outlet strut. A significant variation in the impact loads of the four valves was measured for identical experimental conditions suggesting that valve specific factors influence outlet strut loads. CONCLUSIONS: This study provided an understanding of the cause-effect relationship between valve dynamics and outlet strut fracture.

Biomechanical Phenomena↗
PubMed1976

Ultrasonic detection of cardiovascular flow disturbances.

Blood flow that is disturbed or turbulent may have a significant effect on the development of cardiovascular disease. A method is presented here for detecting periods of disturbed flow using autocorrelograms of the audio signal from a pulsed ultrasound Doppler velocity meter (PUDVM). Autocorrelograms describe quantitatively how the form of a signal changes over time. We produced steady laminar and turbulent pipe flow in a hydraulic test tank, and computed autocorrelograms of the audio signal of the centerline velocity as detected by the PUDVM using fast Fourier transform techniques. We have shown that the autocorrelation coefficient averaged over a short length of time (64 ms) is significantly higher for laminar than for turbulent flow. We have also produced pulsatile flow in our hydraulic tank and computed the mean autocorrelation coefficient at different phases of the flow cycle. The regions of disturbed and undisturbed flow were predicted from the steady flow results. The disturbed flow first appears during the period of the highest forward velocities. These results indicate that the mean autocorrelation coefficient can serve as an indicator of the presence of flow disturbances.

Cardiovascular Diseases↗
PubMed1995

An MR compatible flow simulator for intravascular pressure simulation.

An MR compatible flow simulator is described which generates physiologically realistic pressure and flow waveforms. The simulator is based on a servomotor-driven gear pump which produces pulsatile flow by modulation of the servomotor rotation rate. Operation of the simulator is under the control of a personal computer, which executes an iterative feedback loop to minimize errors between measured and desired pressure waveforms. The simulator is totally automatic, requiring only a few minutes of iteration to generate the desired pressure waveform. Accurate sinusoidal waveforms with frequencies up to 10 Hz have been generated using the simulator, with high-frequency contamination of the measured waveform at least 80 dB below the fundamental frequency. Aortic waveforms have been produced with realistic flow rates and pressure variations. The pump assembly is mechanically straightforward and can operate at an 8-m distance from the flow phantom to allow the device to be isolated from the MR magnet room.

Biophysical Phenomena↗
PubMed2000

In vitro hydrodynamic characteristics among three bileaflet valves in the mitral position.

The non-fully open phenomenon of the advancing standard medical bileaflet heart valves (the ATS valve) are frequently observed in clinical cases, even though there is no problem with their hemodynamic function. The movement of the leaflets was affected easily by the transvalvular flow because of the unique open pivot design of the ATS valve. In this paper, a comparative in vitro hydrodynamic test was conducted among 3 different types of bileaflet valves, and the effect of different shapes of downstream conduits, which induce different transvalvular flow, on hydrodynamic performance was studied. Three bileaflet valves, the ATS valve, CarboMedics valve (CM), and St. Jude Medical valve (SJM), with an annulus diameter of 29 mm for the mitral position were chosen throughout our experiments. First, pressure drops across the valves under steady flow were measured. Then, the valves were tested at the mitral position with our pneumatically driven pulsatile pump. In this pulsatile flow study, 2 different conduits (straight shape and abrupt enlargement shape) were in turn incorporated at the downstream portion of the mitral valve. A high-speed video camera was employed to observe leaflet movements. In a steady-flow test, the ATS and the SJM produced the same pressure drop, but the CM recorded a higher value. In the pulsatile study, it was observed that the ATS leaflets did not open fully in the mitral position when the downstream conduit with an abrupt enlargement shape was incorporated. However, the CM and the SJM always indicated a fully open movement regardless of the shape of downstream conduits. When the straight downstream conduit was incorporated, the ATS produced a similar pressure drop to that of the SJM, which coincided with the steady test results. When the enlargement conduit was incorporated, however, the ATS presented the lowest pressure drop despite the non-fully open movement. The conduit shape at the valve downstream had a significant influence on the closing volume. These findings indicate that the conduit shape at the valve outlet can affect the hydrodynamic characteristics of bileaflet valves.

Blood Pressure↗
PubMed1999

A novel perfusion system for the endothelialisation of PTFE grafts under defined flow.

OBJECTIVES: to develop a perfusion system for culturing human endothelial cells on small-diameter PTFE grafts under defined pulsatile shear stress. METHODS: to benefit from a stronger adhesion of endothelial cells to the substrate, we developed a perfusion system which enables culture of endothelial cells on PTFE grafts to confluence under a wide range of shear stress. We also developed an in situ staining method for the determination of the endothelialisation stage by upper light microscopy. RESULTS: the application of pulsatile flow with high shear stress (6.6 dyn/cm2, 5 min) to a graft endothelialised under perfusion did not lead to a disruption of the confluent cell layer. In contrast, a shear stress of 3 dyn/cm2 applied for 5 min was sufficient to wash more than 50% of endothelial cells off the PTFE graft when cultured to confluence under static conditions. CONCLUSIONS: this technique induces a stronger cell adherence of endothelial cells to a PTFE graft in comparison with grafts endothelialised under static conditions. Endothelialised vascular grafts can be pre-conditioned to defined shear stress values.

Blood Vessel Prosthesis↗
PubMed1991

Measurement of blood flow velocity in retinal vessels utilizing laser speckle phenomenon.

The laser speckle phenomenon was applied to the measurement of the blood flow velocity in glass capillary tubes and human retinal vessels. The instrument consists of a fundus camera, a He-Ne laser, a photomultiplier, a photon-counting unit, a digital correlator, and a microcomputer system. The scattered laser beam from the retina was detected by the photomultiplier and these signals were processed by the photon-counting unit. The digital correlator and the microcomputer calculated the autocorrelation function of these processed signals. The power of the laser beam was 18 mW/cm2, which was sufficiently below the minimum level considered hazardous to the retina. This technique did not require fine optical alignment and the measurement could be done in 1.05 seconds. A linear relationship between the blood flow velocities in glass capillary tubes and the reciprocal of the correlation time was proved, and the pulsatile flow of a human retinal artery was demonstrated. The reproducibility of the method was 12.4 +/- 6.5% in arteries (Mean +/- SD, n = 4) and 12.4 +/- 5.1% in veins (Mean +/- SD, n = 16). The mean blood flow rate in retinal vessels obtained in this experiment agreed with the values of previous studies. This technique utilizing the laser speckle phenomenon is useful in clinical application to measure the retinal blood flow velocity.

Adult↗
PubMed1989

[Synchronous pulse changes in contrast density during carotid angiography].

The relationship between maximal contrast density in DSA and blood flow in doppler sonography was examined in tube model studies and in carotid angiography. During pulsatile flow, pulse-synchronous changes of contrast density can be registered. The maxima of opacification coincide with the doppler-sonographic phase of re-increasing blood flow after a preceding depression. This is caused by the accumulation of contrast medium at the tip of the catheter during diastole and the subsequent dilution of contrast medium by the increasing blood flow during systole. In model studies as well as in angiography, the time interval between the doppler-sonographic maximum of flow and the maximum of contrast density is very constant and is prolonged with increasing distance from the tip of the catheter. This latency between 2 maxima which are registered at the same region of interest, is caused by the higher speed of propagation of the flow wave compared to the actual movement of the blood corpuscles and contrast medium. The understanding of the relationship between cardiac action, blood flow, and contrast density may improve the functional interpretation of angiograms.

Adult↗
PubMed1998

Quantification of aortic regurgitant volume by a newly developed automated cardiac flow measurement method: an in vitro study.

BACKGROUND: Quantifying regurgitant volumes is important for treatment of patients with valvular aortic regurgitation. Simple, reliable methods to quantify aortic regurgitation have been sought both in the catheterization laboratory and the echocardiography laboratory. OBJECTIVES: The aim of our study was to investigate the applicability of a new automated cardiac flow measurement method with color Doppler velocity data for quantifying retrograde flow volumes of aortic regurgitation in an ascending aorta model. METHODS AND RESULTS: A 2-chamber pulsatile flow system with a modeled ascending aorta and a regurgitant aortic valve orifice was developed. The model could generate "aortic regurgitation-like" waveforms through the use of an electrically controlled valve. The regurgitant flows through the orifice (8.5 to 28.1 mL/beat) were measured by an ultrasound flowmeter; they were also calculated in the ascending aorta 1.0 cm above the orifice by the automated cardiac flow measurement method, which integrated spatially distributed digital flow velocity data through "diastole." Calculated regurgitant volumes measured with the low color Doppler filter (5.4 cm/s) agreed well with those measured with the flowmeter (r=.99, P < .001, mean difference=2.2+/-3.7 mL). However, the regurgitant volume was underestimated when 2 higher filter settings were used (9.6 and 10.9 cm/s). Although there was no significant difference in mean volume, higher frame rate (19 frames/s) provided more reproducible results with smaller standard deviation as compared with lower frame rate (7 frames/s). CONCLUSIONS: This new automated cardiac flow measurement method appears to be promising for semiautomatic quantification of aortic regurgitant volume. Appropriate choice of filter setting and high frame rate assists reliable data acquisition.

Aorta↗
PubMed2003

Flow changes in the aorta associated with the deployment of a AAA stent graft.

The purpose of this study was to investigate the hemodynamic implications of a proximal shift in the aortic bifurcation that results from abdominal aortic aneurysm (AAA) stent graft deployment. A flow model was constructed in which an anatomically accurate model of the aorta was subjected to physiologic pulsatile flow. The model included the celiac, superior mesenteric, left and right renal arteries. The aortic bifurcation, leading to the right and left iliac arteries was included, as well as the lumbar curvature. Flow simulations were performed under resting and mild exercise conditions with and without a Cordis AAA stent graft deployed. Flow patterns were visualized with dye injection and recorded onto video. The flow rates through the iliac and renal arteries were continuously monitored using ultrasonic flowmeters. Flow visualization revealed that flow disturbances at the level of the renal arteries were slightly increased with the deployment of the stent graft. The orientation of the endolegs within the aorta had no perceptible effect on these disturbances. Under mild exercise conditions, very little flow disturbance was observed. In conclusion, there are slight changes in flow disturbance near the renal arteries due to stent graft deployment, but these changes would not be expected to have significant clinical implications.

Aorta↗
PubMed1991

Color modulation of Doppler spectra with the use of a personal computer.

This paper describes a method for the use of a personal computer in developing color modulated spectral maps of blood flow echoes from a Doppler flowmeter. The acoustical signal from a Doppler flowmeter is digitized and transformed into the frequency domain with a fast Fourier technique with the use of an Apple IIe microcomputer in conjunction with a Motorola 68000 co-processor. The resultant transform is displayed as a pseudo three-dimensional, color modulated spectral map by way of a color monitor, or a television projector onto the meeting room screen. We have found this technique to be useful in appreciating differences in blood flow from different hydraulic conditions, as well as in helping the medical students appreciate these differences in pulsatile flow in various arteries.

Color↗
PubMed1995

Hemodynamics of an artery with mild stenosis.

In this study the hemodynamics in the early stages of the atherosclerotic process--when a neointimal hyperplasia or an intimal fibrocellular hypertrophy takes place--is theoretically investigated. A local, slight increase in the wall thickness of a canine femoral artery is simulated using an original two-dimensional mathematical model of arterial hemodynamics and the effects induced on the velocity field by the simulated mild stenosis--only 2% of area reduction--are analysed. The model incorporates: fluid non-linear inertial forces, viscoelastic wall motion, anatomical taper, unsteady flow, pressure propagation and reflections on both the proximal and distal vessel ends. Two different physiological pulsatile flows are considered: a basal flow condition and a light vasodilation state inducing in the vessel segment a limited increase in mean flow (50%). The distribution along the vessel during the cardiac cycle of both the velocity profile and wall shear stress, are shown. The shape of velocity distributions is strongly perturbed by the stenosis and disturbances are clearly evident whatever instant of the cardiac cycle is considered. After vasodilatation, during the phase of systolic deceleration, a vortex circulation appears in the post-stenotic region. The vortex persists for the whole diastolic phase, causing a very strong stress at the arterial wall: wall shear stress in the distal part of the simulated mild stenosis is at least five times the basal value. The reported results provide a coherent explanation of the critical role that hemodynamic factors may play in the early stages of atherogenic process.

Algorithms↗
PubMed1994

Validity of pulsatile ocular blood flow measurements.

The determination of average net pulsatile ocular blood flow form measurements of the intraocular pressure (IOP) pulse is based upon 1) an accurate measurement of IOP and its time variation; 2) a knowledge of the relation between the volume of the living eye and its IOP; 3) a physical model for the flow of blood through the eye: and 4) a concept of steady venous outflow from the eye. Each of these premises needs to be examined. The present analysis assesses the validity of the pneumatic tonometer for measuring the pressure in a flowing column of gas that is directed toward a thin membrane that is in contact with the surface of the cornea. The pressure of this stream of gas exerts a force against the cornea that depresses the corneal surface against the opposing force of the IOP. The balance of these forces and the resultant effect on the tonometer pressure sensor is described by the theories of elasticity, thermodynamics and fluid mechanics. In this treatment, differential equations are solved for the elastic deflections of the cornea subject to the opposing intraocular and tonometer pressures. This permits the pressure in the chamber of the pneumatic tonometer to be related through first principles to the IOP. The response of the tonometer pressure sensor to a range of IOPs (5-60 mmHg) is obtained, as well as the dynamical response of the tonometer to IOP oscillations. The conclusion is that the pneumatic tonometer provides a high fidelity, noninvasive measure of the IOP and its time variation.(ABSTRACT TRUNCATED AT 250 WORDS)

Blood Flow Velocity↗