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PubMed2002

The use of pulsatile flow to separate species.

Pulsatile motion greatly enhances the mass transfer of a dilute species compared to that due to pure molecular diffusion. If two dilute species are present in a carrier, the mass transfer of the faster diffusing species may be higher, lower, or the same as the slower diffusing species. This depends on the time constants associated with the system and the ability of a species to remain in the fast moving portion of the flow field. The difference in the mass transfer of each species can lead to a separation that can be used in a number of processes including the removal of carbon dioxide from the air. This phenomenon is modeled in an open tube geometry and in the annular space between two concentric cylinders. In annular pulsatile flow, the effect of the inner cylinder being off center from the outer cylinder on the mass transfer and separation is also analyzed. Finally, experimental results are presented to prove the validity of the models and the separation that can be achieved using this process.

Journal Article↗
PubMed1981

Plasma vasopressin levels and urinary sodium excretion during cardiopulmonary bypass with and without pulsatile flow.

The use of pulsatile perfusion during bypass should create a more physiological milieu and thus attenuate the vasopressin stress response. To determine this, 20 patients scheduled for elective coronary artery bypass operation were studied in two groups. Group 1 had a standard nonpulsatile perfusion, and in Group 2 a pulsatile pump was used. Measurements were made before and after anesthesia, after surgical incision, and at 15 and 30 minutes during and after cardiopulmonary bypass. In both groups, vasopressin levels were significantly elevated after sternotomy (4.5 +/- 1.5 to 37 +/- 10 pg/ml in Group 1 and 3.1 +/- 1.2 to 33 +/- 9 pg/ml in Group 2, p less than 0.05) and during bypass (198 +/- 19 pg/ml in Group 1 and 113 +/- 16 pg/ml in Group 2) but were higher in Group 1 (p less than 0.05). With comparable perfusion pressures in both groups, Group 2 required higher flow (4.2 +/- 0.2 versus 3.5 +/- 0.3 L/min, p less than 0.05) and had lower resistance (1,351 +/- 182 versus 1,841 +/- 229 dynes sec cm-5, p less than 0.05) and higher urine Na+ (123 +/- 5 versus 101 +/- 8 mEq/L, p less than 0.05). These data demonstrate that pulsatile flow can significantly attentuate the vasopressin stress response to bypass. Since vasopressin, at these concentrations, is a potent vasoconstrictor and is capable of producing a Na+ diuresis, this may partially explain the higher flow requirements and the decrease in Na+ excretion.

Blood Pressure↗
PubMed1988

Preliminary pulsatile flow bench validation of a thermodilution right ventricular ejection fraction system.

A preliminary Pulsatile Flow Bench validation of the REF-1 Right Ventricular Ejection Fraction (RVEF) computer and catheter system was performed to determine the accuracy of the current REF-1 system. These results reflect the accuracy of the current REF-1 system and not the final REF-1 system that will be released at a later date. The Pulsatile Flow Bench cardiac output and ejection fraction ranges included in this study are 1 to 6 Lpm and 15% to 60%, respectively. Currently, plans are being made to increase the flow bench cardiac output range to 10 Lpm with ejection fractions up to 70%. The results of this study show a correlation coefficient of 0.94 (adjusted R-square) between flow bench ejection fractions and REF-1 system ejection fractions. Also, the correlation coefficient between flow bench cardiac output and REF-1 system cardiac output was determined to be 0.99 (adjusted R-square).

Calibration↗
PubMed1988

Apparent stresses in disturbed pulsatile flows.

Traditional attempts at decomposing measured velocities into repeatable and random components are examined for a set of velocity data measured under pulsatile flow conditions distal to a 90% axisymmetric constriction. The Reynolds numbers, which are typical of those found in the human carotid artery, are such that transitional phenomena occur during portions of the pulsatile cycle at several axial stations. The implications of the method selected for velocity decomposition upon the computation of fluctuating or 'apparent' stresses is a point of major focus. It is shown that the usual estimation of Reynolds stresses in a pulsatile flow by subtracting the ensemble-averaged velocity from the instantaneous velocity leads to an underestimation of the apparent stress when coherent or repeatable disturbances exist in the flow. An alternative decomposition using a frequency domain approach is presented which combines both random and coherent stresses into a single apparent stress, and it is proposed that this approach is preferable to the traditional ensemble averaging method when estimating fluctuating stresses in arterial flows.

Blood Flow Velocity↗
PubMed2004

First-pass scintigraphy with (99m)Tc macroaggregated albumin: a method for evaluating pulmonary arterial flow pulsatility.

OBJECTIVES: The aim of this work was to develop and describe a non-invasive scintigraphic technique to detect flow pulsatility in peripheral pulmonary arteries. METHODS: Ten normal volunteers were submitted to a first-pass scintigraphy using Tc macroaggregated albumin (Tc-MAA). A time-activity curve was generated for the right lung lateral third. Activity was shown to be restricted to the arterial compartment of the lungs, since there was no detectable progression of the radiopharmaceutical to the systemic circulation. Consequently, the rise in lung activity was attributed to the arterial inflow and the first derivative of the time-activity curve was assumed to represent pulmonary arterial flow. RESULTS: Pulmonary flow curves showed two main positive peaks in six volunteers, followed by a third small peak in three others. Flow was predominant during systole, with an important reduction in magnitude before the diastolic peak, leading to a negative count variation in eight subjects. This pattern is comparable to that described in central pulmonary vessels by different methods. CONCLUSIONS: First-pass scintigraphy with Tc-MAA was able to detect flow pulsatility in pulmonary arteries. These results need to be confirmed in a larger number of individuals, and, if shown to be reproducible, may increase our understanding of lung flow physiology, and of its modifications in the presence of cardiopulmonary diseases.

Adult↗
PubMed2000

Physiological basis of flow dependence of Gorlin formula valve area in aortic stenosis: analysis using an hydraulic model of pulsatile flow.

BACKGROUND AND AIM OF THE STUDY: The study aim was to clarify the basis of the cardiac output dependence of aortic valve area calculated with the Gorlin formula which has been reported in patients with aortic stenosis. Clinical and experimental studies which have attempted to differentiate between a change in physical orifice area, versus a defect in the Gorlin formula as the cause of cardiac output related variations in Gorlin valve area in aortic stenosis have yielded conflicting results. METHODS: We employed a numerical model of pulsatile flow in which the total instantaneous transvalvular gradient was the sum of the convective and viscous pressure losses and pressure recovery beyond the stenosis. By analogy with other hydraulic devices, viscous losses due to stenosis were modeled by the term KfV(EXP), where V is flow velocity. Kf and EXP were determined for various orifices by adjusting these two parameters to obtain excellent fit between curves of the orifice discharge coefficient based upon the expression KfV(EXP), and empirically measured orifice discharge coefficient curves which have been published in the engineering literature. Mean systolic transvalvular gradient was calculated from the total instantaneous transvalvular gradient values for an assumed jet area, and an assumed systolic time-velocity flow profile. This mean gradient was substituted into the Gorlin equation to find the apparent Gorlin valve area at cardiac outputs varying from 0 to 10 l/min for a range of where V is assumed true areas between 0.5 and 2.0 cm2. RESULTS: For functional valve areas <1.5 cm2, viscous losses resulted in at most a 10-12% fall in apparent Gorlin valve area when cardiac output was decreased from 5 to 2.5 l/min. In addition, maximum viscous losses did not result in a pressure-flow relationship which was closer to linear than to quadratic. which the CONCLUSION: Clinically significant changes in valve area with flow are due to orifice area changes rather than Gorlin formula flow variability. Moreover beyond the Gorlin valve area is preferred over valve 'resistance' for assessing stenosis severity. In low cardiac output states, output should be increased to the normal range before Gorlin valve area is measured.

Aortic Valve↗
PubMed1998

Determination of prestenotic flow volume using an automated method based on colour Doppler imaging for evaluating orifice area by the continuity equation: validation in a pulsatile flow model.

OBJECTIVE: To evaluate, in a pulsatile flow model simulating flow conditions in valvar stenoses, whether accurate determination of orifice area can be achieved by the continuity equation using automated determination of flow volumes based on spatiotemporal integration of digital colour Doppler flow velocities. METHODS: A method for automated determination of flow volumes which takes into account the velocity distribution across a region of interest was examined using flow through a tube and various restrictive outlet orifices with areas ranging between 0.2 and 3.1 cm2. The sampling rectangle of the Doppler method was positioned proximal to the obstructions within the flow convergence zone for evaluating prestenotic flow volume. Stenotic jet velocities were recorded by continuous wave Doppler to obtain the integral under the velocity curve. Prestenotic flow volume was then divided by the velocity integral to calculate functional orifice area according to the continuity equation. RESULTS: The presence of parabolically shaped velocity profiles across the prestenotic region was demonstrated by the Doppler method. Excellent agreement was found between prestenotic flow volumes measured by the Doppler technique and actual values (r = 0.99, SEE = 1.35 ml, y = 0.99x-0.24). Use of the continuity equation led to a close correlation, with a systematic underestimation of geometric orifice sizes. Correction of Doppler data for flow contraction yielded an excellent agreement with actual orifice areas. CONCLUSIONS: The study validated the accuracy of a Doppler method for automated determination of flow volumes for quantifying orifice area by the continuity equation. Prestenotic flow volume and functional orifice area could be evaluated reliably in the presence of non-flat velocity profiles. Thus the method contributes to the non-invasive assessment of valvar stenoses.

Echocardiography, Doppler, Color↗
PubMed1983

Complement activation during cardiopulmonary bypass: quantitative study of effects of methylprednisolone and pulsatile flow.

Forty four patients undergoing open heart surgery were divided into three groups. Group 1 (17 patients) underwent routine anaesthesia and surgery; group 2 (17 patients) received two doses of methylprednisolone (30 mg/kg), one during induction of anaesthesia and the other immediately before induction of cardiopulmonary bypass; and group 3 (10 patients) received pulsatile flow while undergoing pulsatile perfusion by the heart-lung machine. A modification of the previously described technique was used to detect and measure complement activation in plasma before and during the bypass period using crossed immunoelectrophoresis. About 45% of all patients showed measurable complement activation (greater than 4.5%) during cardiopulmonary bypass and the mean activation in this group was 6.4%. There was no significant difference between the three groups in complement activation. In group 2, however, women showed significantly more complement activation than men (p less than 0.05). It is suggested that neither corticosteroids nor pulsatile flow affect complement activation, but caution should be exercised in women receiving methylprednisolone.

Animals↗
PubMed1976

A new method of producing pulsatile flow during cardiopulmonary bypass using a standard roller pump.

A new method for producing pulsatile flow during cardiopulmonary bypass is described. The method requires only the addition of a dilated segment in the tubing which passes beneath the arc of a standard roller pump. Preliminary studies demonstrate that pulsatile flow and pressure with physiologic contours can be produced by this "bubble tube" system. Furthermore, the new tubing causes less hemolysis than standard pump tubing.

Animals↗
PubMed2003

Applications of the pulsatile flow versatile ECLS: in vivo studies.

INTRODUCTION: T-PLS (Twin-Pulse Life Support) is the first commercial pulsatile ECLS (Extra Corporeal Life Support) device (1). The dual sac structure of T-PLS can effectively reduce high membrane oxygenator inlet pressure and hemolysis. To verify both the use of T-PLS for ECLS and the advantages of T-PLS, we tested various models. METHOD AND RESULTS: In the partial CPB (cardio pulmonary bypass) model (swine), T-PLS (N = 6), and Biopump (N = 2), a single pulsatile pump (N = 2), were compared. In the case of single pulsatile flow, during pump systole, pressure increased to 700 - 800 mmHg at the inlet port of the membrane oxygenator. fHb, a hemolysis measurement value, was about 80 mg/dL at 3 hours. On the contrary, because of T-PLS's dual sac system, the pressure of T-PLS had a maximum value of about 250 mmHg and fHb was similar to that of the commercial centrifugal pumps. In the total CPB model (bovine, N = 6), the heart was stopped via cardioplegia (Kcl). T-PLS flow was maintained at 3.0-4.5 L/min. T-PLS functioned like a natural heart, having a pulse pressure of 26-43 mmHg and a pulse rate of 40-60 bpm (beats per minute). In the emergency case model (canine, N = 6), T-PLS was started 10 minutes after cardiac arrest from electronic shock. In spite of cardiac arrest for a period of 40 minutes, the heart was recovered after defibrillation. In the ARDS (Acute Respiratory Distress Syndrome) model (canine, N = 6), minimal ventilator parameters were set: tidal volume 130 ml, respiration rate = bpm, FiO2 = 10%. Three hours after starting T-PLS, PO2 of the carotid artery blood (after 2 hours: 195 +/- 89.4; after 3 hours: 258 +/- 99.3 mmHg) was above half the value of the femoral artery but was within normal range. CONCLUSION: It is suggested that a portable pulsatile ECLS like T-PLS may be used as a CPB device and as an alternative CPR (cardiopulmonary resuscitation) device in the case of cardiac arrest. Due to the pulsatile flow, oxygenated blood is delivered to the patient without overloading the ARDS patients heart.

Animals↗
PubMed1987

Analysis of spin-echo rephasing with pulsatile flow in 2D FT magnetic resonance imaging.

The effects of pulsatile flow on spin phases in spin-echo magnetic resonance imaging are considered. General expressions for the spin phases of the first four echoes are derived in terms of the Fourier coefficients of flow. These expressions are valid for any time-dependent acceleration and, hence, are not restricted to constant acceleration. The derived expressions are then theoretically evaluated for aortic flow and examined at different points in the cardiac cycle. Our results show that rephasing may occur at certain points in the cardiac cycle for either even or odd echoes depending upon the particular Fourier coefficients of the velocity function and the spin-echo delay time. However, even-echo rephasing is not always necessarily valid. Furthermore, the possibility of determining the flow velocities in the body with an appropriate series of imaging studies is also discussed.

Aorta↗
PubMedDate not supplied

High-speed black blood imaging of vessel stenosis in the presence of pulsatile flow.

Stenosis phantoms were created to study the ability of "black blood" methods to image a vessel stenosis in the presence of pulsatile flow. Black blood images were acquired with a modified TurboFLASH (fast low-angle shot) method that eliminates flow signal by applying a set of prepulses before segmented data acquisition. With this high-speed approach, imaging can be completed within 16 seconds. This technique was compared with conventional spin-echo black blood, gradient-echo black blood, and gradient-echo bright blood methods. Loss of flow signal, which extended beyond the site of the stenosis, was seen on the gradient-echo bright blood images. The pattern of signal loss varied with the type of stenosis. Flow voids were achieved with spin-echo black blood imaging; however, substantial ghosting artifacts were seen. With gradient-echo black blood imaging, it was difficult to eliminate all flow signal, particularly for in-plane flow. The modified TurboFLASH method produced high-quality black blood images in a fraction of the time needed for spin-echo imaging. It showed no ghosting artifacts even in the presence of pulsatile flow.

Blood Flow Velocity↗
PubMed1985

Simple pulsatile flow in an artery with a constriction.

A smooth isolated, axisymmetric occlusion in a straight vascular tube is a tractable problem for pulsatile flow calculations via finite-difference approximations to the Navier-Stokes equation. Steady flow depends on the Reynolds number and two geometric parameters which describe the stenosis. The mere addition of a simple harmonic to the mean flow adds two more parameters. One is the reduced frequency, or Strokes number, and the other epsilon, the ratio of unsteady to steady flux. After describing steady stenosis flow examples, the dynamic patterns of pulsatile flow are illustrated indicating the inadequacy of basing hypotheses of atherosclerosis on mean (steady) flow.

Arterial Occlusive Diseases↗
PubMed1975

Improvement of myocardial and other vital organ functions and metabolism with a simple method of pulsatile flow (IABP) during clinical cardiopulmonary bypass.

A simple, safe, and effective method of producing pulsatile flow during cardiopulmonary bypass (CPB) with intra-aortic balloon pumping (IABP) was used in 56 patients. No complications were associated with IABP. Myocardial metabolic studies, including coronary sinus lactates, mycoardial venous-arterial lactate differences, myocardial lactate extraction, and "excess lactate" were determined serially during the first hour of CPB. Changes in myocardial metabolism were statistically less abnormal in pulsatile flow (PF) patients when contrasted with a comparable group of nonpulsatile flow (NPF) patients. The changes were probably myocardial in origin since alterations in arterial lactates and lactate/pyruvate ratios were similar in both groups. In a comparable group of coronary bypass NPF patients, the percentage of left ventricular ejection fractions fell during the immediate postoperative period, whereas it rose in the PF group. Over-all body tissue injury (lactic dehydrogenase) and probably hepatocellular injury (serum glutamic oxalacetic transaminase) were less apparent in the PF patients. Postoperative low-cardiac-output syndrome did not occur in the PF patients and supportive drugs and diuretics were not needed. PF does not produce excessive hemolysis. This procedure may improve mortality rates by improving myocardial and other vital organ perfusion and by sustaining their function during weaning from CPB. This technique may prove superior to other forms of PF and is indicated in patients with severe left ventricular or other vital organ dysfunction and/or prolonged CPB.

Aspartate Aminotransferases↗
PubMed1976

A simple device to obtain a pulsatile flow. Application to the vascular perfusion of dogs isolated intestinal segments.

A simple device allowing a pulsatile flow to be obtained in isolated organ perfusion has been developed and applied to the vascular perfusion of isolated canine jejunal segments. The principle of the device consists of superimposing on a constant pressure produced by a roller pump, a pulsatile pressure of which the amplitude, frequency, and shape of the pulses can be adjusted separately and independently of the mean pressure value. The role of the arterial pulse in intestinal vascular perfusion has been studied by comparing the hemodynamic and metabolic behavior during alternate periods of pulsatile and nonpulsatile pumping. While no striking change in vascular resistance was observed, the O2 consumption was significantly increased under pulsatile flow. These results testify to better metabolic conditions and enhanced organ functions under pulsatile pumping and also argue for improved intestinal microcirculation despite the constancy of the vascular resistance.

Animals↗
PubMed1977

[Hydredynamic bench for pulsatile flows. Application to hemodynamic studies (author's transl)].

Oscillatory or pulsatile flows are produced on a hydrodynamic bench by a volumetric gear pump. The moto-pump group is an original device which is very different from other systems. It is driven by a wave synthesizing generator which enables any flow rate to be produced especially oscillatory, pulsatile or physiological flow. The synthesizing generator delivers a periodic wave with variable amplitude, shape and frequency. The moto-pump group is controlled by an amplifying comparator; it produces a flow whose rate follows the control signal. A study of the modifications of flow patterns induced by models of vascular stenoses has been performed with this bench. The study of the velocity distribution has been effected with a pulsed Doppler ultrasonic velocimeter.

Biomedical Engineering↗
PubMed1978

Pulsatile flow in hemodialyzers.

The present work is concerned with the calculation of NaCl transfer in flowing solutions and its dependence upon flow characteristics at hemodialyzers. A theoretical analysis of the solute transfer in a hemodialyzer is presented. Experiments were carried out with a continuous flow flat-plate dialyzer. Permeability of cuprophane membranes were calculated both for pulseless and pulsatile flows. It was found that the membrane permeability increases with flow rate but the asymptotic value of pulsatile flow is remarkably higher than that of the pulseless flow. The difference between the transfer capabilities of the two flow regimes was found to be more than 100 percent.

Humans↗
PubMedDate not supplied

Pulsatile flow artifacts in two-dimensional time-of-flight MR angiography: initial studies in elastic models of human carotid arteries.

Initial experimental and numerical analysis of artifacts due to pulsatile flow in two-dimensional time-of-flight (2D-TOF) magnetic resonance (MR) angiography are presented. The experimental studies used elastic models of the carotid artery bifurcation cast from fresh cadavers and accurately reproducing the twisting and tapering of the human blood vessels, allowing direct comparison of images with and without flow. Prominent image artifacts, including periodic ghosts and signal loss, were produced by pulsatile flow even though flow-compensated gradient waveforms were used. The dependence of artifacts due to partial saturation on pulse sequence parameters (TR and flip angle) was investigated theoretically for a simple pulsatile velocity profile and compared with experimental results from a model of a normal carotid artery. Signal reduction was observed proximal and distal to the stenosis in a model with a 70% internal carotid artery (ICA) stenosis and a model with 90% stenoses in both the ICA and the external carotid artery. Although this study deals exclusively with 2D-TOF imaging, the methods can also be applied to evaluate other MR angiography techniques.

Artifacts↗