Effect Of Pulsatile Blood Flow Research Articles

The effect of pulsatile blood flow during proximal graft in facilitation weaning from cardiopulmonary bypass pump in coronary artery bypass graft surgery

The effect of pulsatile blood flow during proximal graft in facilitation weaning from cardiopulmonary bypass pump in coronary artery bypass graft surgery

Effects of Pulsatile Blood Flow on Oxygenator Performance.

Extracorporeal membrane oxygenation (ECMO) is mainly used for the therapy of acute respiratory distress syndrome and chronic obstructive lung disease. In the last years, the development of these systems underwent huge steps in optimization, but there are still problems with thrombus formation, clogging, and thus insufficient gas exchange. One idea of ECMO optimization is a pulsatile blood flow through the oxygenator, but this is still a controversy discussion. Analyzing available publications, it was not possible to identify a general statement about the effect of pulsatile blood flow on the gas exchange performance. The variety of parameters and circuit components have such a high influence on the outcome that a direct comparison of the studies is difficult. For this reason, we performed a structured study to evaluate the effects of pulsatile blood flow on the gas exchange performance of oxygenator. In in vitro tests according to DIN EN ISO 7199, we tested a small oxygenator (0.25 m2 exchange surface, polymethylpentene fibers, 33 mL priming volume) with constant and pulsatile blood flow in comparison. Therefore, we varied the mean blood flow from 250 to 1200 mL/min, the amplitude of 0, 20, and 50%, and the frequency of 30, 60, and 90 bpm. The results demonstrate that the gas transfer for pulsatile and constant blood flow was similar (oxygen: 36-64 mLO2 /LBlood ; carbon dioxide 35-80 mLCO2 /LBlood ) for the same mean blood flow ranges. Over all, the results and analyses showed a statistically nonsignificant difference between pulsatile and nonpulsatile flow. Consequently, we conclude that the implementation of pulsatile blood flow has only a small to no effect on the gas exchange performance in an oxygenator. As the results were obtained using an oxygenator with a coiled fiber bundle, the test must be verified for a stacked fiber oxygenator.

Effect of pulsatile blood flow on LDL transport in arterial layers

Effect of pulsatile blood flow on LDL transport in arterial layers

Effect of pulsatile blood flow on LDL transport in arterial layers

Considering the pulsatile nature of blood flow, the transport of low density lipoprotein (LDL) species in the arterial wall has been numerically analysed. A straight axi-symmetric arterial segment with four arterial porous layers vis. endothelium, intima, internal elastic lamina and media has been taken into consideration. These layers are considered porous in nature. For modelling the fluid flow in the lumen and the arterial wall, Navier-Stokes equation and Darcy's equation have been used respectively. The solute flow modelling in the lumen and in the arterial wall has been done by using convection-diffusion equation and convection-diffusion-reaction equation respectively. Simple pulsatile and physiological pulsatile model of blood flow have been considered in the present analysis. The present study shows that the physiological pulsatile flow is having more impact on the radial filtration velocity at lumen-endothelium interface than that of the case for simple pulsatile nature of flow. Therefore, the possibility of enhancement in solute transport in the arterial wall is more in case of physiological pulsatile nature of flow.

Effect of Pulsatility on Microcirculation in Patients Treated with Extracorporeal Cardiopulmonary Resuscitation: A Pilot Study.

The effect of pulsatile blood flow on microcirculation during extracorporeal cardiopulmonary resuscitation (ECPR) is not elucidated; therefore, we designed an observational study comparing sublingual microcirculation in patients with refractory cardiac arrest (CA) with spontaneously pulsatile or low/nonpulsatile blood flow after treatment with ECPR. Microcirculation was assessed with Sidestream Dark Field technology in 12 patients with CA who were treated with ECPR and 12 healthy control subjects. Microcirculatory images were analyzed offline in a blinded fashion, and consensual parameters were determined for the vessels ≤20 μm. The patients' data, including actual hemodynamic parameters, were documented. Pulsatile blood flow was defined by a pulse pressure (PP) ≥ 15 mm Hg. Compared with the healthy volunteers, the patients who were treated with ECPR exhibited a significantly lower proportion of perfused capillaries (PPC); other microcirculatory parameters did not differ. The groups of patients with pulsatile (n = 7) versus low/nonpulsatile (n = 5) blood flow did not differ in regards to the collected data and hemodynamic variables (except for the PP and ejection fraction of the left ventricle) as well as microcirculatory parameters. In conclusion, microcirculation appeared to be effectively supported by ECPR in our group of patients with CA with the exception of the PPC. We found only nonsignificant contribution of spontaneous pulsatility to extracorporeal membrane oxygenation-generated microcirculatory blood flow.

Numerical investigation of the influence of pulsatile blood flow on temperature distribution within the body of laser-irradiated biological tissue phantoms

The present work is concerned with the numerical investigation of the effects of pulsatile nature of blood flow in large size blood vessels on temperature distribution in laser-irradiated biological tissue phantoms. Phenomenon of light propagation through the tissue–blood vessel domain is modelled by transient radiative transport equation (RTE). Discrete ordinate method has been employed to solve transient form of RTE. In order to determine the temperature distribution inside the tissue–blood vessel domain, the solution of RTE has been coupled with the energy equation. Pulsatile nature of velocity profile has been employed at the inlet of the blood vessel. Navier–Stokes equations have been solved for determining the velocity field required to understand the effect of pulsatile blood flow on the temperature distribution. Relative influence of various parameters such as heart beat rate, time-averaged blood inlet velocity and size of the blood vessel on temperature distribution within the blood vessel has been presented. The numerical code developed as part of the present study has first been verified against the results available in the literature for the same operating parameters. Both homogenous as well as tissue phantoms embedded with optical inhomogeneities of different contrast levels have been considered. Results of the study clearly reveal the strong influence of pulsatile nature of blood flow on the resultant temperature distribution in the surrounding tissue region. The increase in temperature due to laser-irradiation is found to be relatively lesser in the presence of blood flow due to its convective cooling effects as compared to the rise in temperature achieved in the tissue phantom without blood vessels.

Functional Magnetic Resonance Imaging of the Lung

Beyond being a substitute for X-ray, computed tomography, and scintigraphy, magnetic resonance imaging (MRI) inherently combines morphologic and functional information more than any other technology. Lung perfusion: The most established method is first-pass contrast-enhanced imaging with bolus injection of gadolinium chelates and time-resolved gradient-echo (GRE) sequences covering the whole lung (1 volume/s). Images are evaluated visually or semiquantitatively, while absolute quantification remains challenging due to the nonlinear relation of T1-shortening and contrast material concentration. Noncontrast-enhanced perfusion imaging is still experimental, either based on arterial spin labeling or Fourier decomposition. The latter is used to separate high- and low-frequency oscillations of lung signal related to the effects of pulsatile blood flow. Lung ventilation: Using contrast-enhanced first-pass perfusion, lung ventilation deficits are indirectly identified by hypoxic vasoconstriction. More direct but still experimental approaches use either inhalation of pure oxygen, an aerosolized contrast agent, or hyperpolarized noble gases. Fourier decomposition MRI based on the low-frequency lung signal oscillation allows for visualization of ventilation without any contrast agent. Respiratory mechanics: Time-resolved series with high background signal such as GRE or steady-state free precession visualize the movement of chest wall, diaphragm, mediastinum, lung tissue, tracheal wall, and tumor. The assessment of volume changes allows drawing conclusions on regional ventilation. With this arsenal of functional imaging capabilities at high spatial and temporal resolution but without radiation burden, MRI will find its role in regional functional lung analysis and will therefore overcome the sensitivity of global lung function analysis for repeated short-term treatment monitoring.

Parametric analysis of effective tissue thermal conductivity, thermal wave characteristic, and pulsatile blood flow on temperature distribution during thermal therapy

This study examines the coupled effects of pulsatile blood flow in a thermally significant blood vessel, the effective thermal conductivity of tumor tissue, and the thermal relaxation time in solid tissues on the temperature distributions during thermal treatments. Due to the cyclic nature of blood flow as a result of the heartbeat, the blood pressure gradient along a blood vessel was modeled as a sinusoidal change to imitate a pulsatile blood flow. Considering the enhancement in the thermal conductivity of living tissues due to blood perfusion, the effective tissue thermal conductivity was investigated. Based on the finite propagation speed of heat transfer in solid tissues, a modified wave bio-heat transfer transport equation in cylindrical coordinates was used. The numerical results show that a larger relaxation time results in a higher peak temperature. In the rapid heating case I (i.e., heating power density of 100Wcm−3 and heating duration of 1s) and a heartbeat frequency of 1Hz, the maximum temperatures were 62.587 and 63.107°C for thermal relaxation times of 0.464 and 6.825s, respectively. In contrast, the same total heated energy density of 100Jcm−3 in a slow heating case (i.e., heating power density of 5Wcm−3 and heating duration of 20s) revealed maximum temperatures of 57.724 and 61.233°C for thermal relaxation times of 0.464 and 6.825s, respectively. In rapid heating cases, the occurrence of the peak temperature exhibits a time lag due to the influence of the thermal relaxation time. In contrast, in slow heating cases, the peak temperature may occur prior to the end of the heating period. Moreover, the frequency of the pulsatile blood flow does not appear to affect the maximum temperature in solid tumor tissues.

Numerical analysis of coupled effects of pulsatile blood flow and thermal relaxation time during thermal therapy

The main purpose of this study is to investigate the coupled effects of the pulsatile blood flow in thermally significant blood vessels and the thermal relaxation time in living tissues on temperature distributions during thermal treatments. Considering the fact that propagation speed of heat transfer in solid tissues is actually finite according to experiments, the traditional Pennes bioheat transfer equation (PBTE) was modified to a wave bioheat transfer equation (WBTE) that contains both wave transportation and diffusion competing with each other and characterized by the thermal relaxation time. The wave behavior will be more dominant when the relaxation time is large. WBTE together with a coupled energy transport equation for blood vessel flow was used to describe the temperature evolution of our current tumor–blood vessel system, and the equations were numerically solved by the highly accurate multi-block Chebyshev pseudospectral method. Numerical results showed that temperature evolution from WBTE was quite different from their counterparts from PBTE due to the dominant wave feature under large relaxation time. For example, larger relaxation time would preserve high temperature longer and this effect is even more pronounced when heating is fast. It further implies that heat is drained more slowly when relaxation time is large, and would make thermal lesion region cover the tumor tissue, the heating target, better. This phenomenon would therefore hint that the traditional PBTE simulations might under-estimate the thermal dose exerted on tumor. As to the pulsation frequency of blood flow from heart beat which was originally predicted to be important here, it turned out that the thermal behavior is quite insensitive to pulsation frequency in the current study.

Effect of Pulsatile Blood Flow on Thrombosis Potential With a Step Wall Transition

It is well known that thrombus can be formed at stagnation regions in blood flow. However, studies of thrombus formation have typically focused on steady state flow. We hypothesize that pulsating flow may reduce persistent stagnation at the sites of low shear stress by decreasing exposure time. In this study, a step-wall transition, which is commonly found on implantable devices, is used as a test bed causing a recirculation vortex. Stagnation at such a step is considered using computational fluid dynamics studies and flow visualization experiments. Parametric studies were performed with varying step height, pulsatility, and velocity. The percentage of time along the wall with shear stresses below a threshold for thrombosis and the total length of wall that maintains contact with stagnant flow throughout the cardiac cycle are calculated. Persistent stagnation occurs at the corner of a step-wall transition in all cases and is observed to decrease with a decrease in step height, an increase in mean velocity, and an increase in pulsatility. Under steady flow conditions, a flow reattachment point resulting from recirculation is observed with expanding steps, whereas a flow separation point is observed with contracting steps. Pulsatility decreases persistent stagnation at the flow separation point with contracting steps, whereas it completely eliminates persistent stagnation at the flow reattachment point with expanding steps. The results of this work conclusively show that stagnation can be reduced by increasing pulsatility and flow velocity and by decreasing step height.

Aortic Reservoir Function is Attenuated Following Acute Endurance and Interval Exercise

Aortic reservoir function is a measure of the aorta to function as a second pump during diastole and attenuate the effects of pulsatile blood flow. The effect of acute high vs. moderate exercise intensity on reservoir function is unknown. PURPOSE: To determine the effect of acute steady state (SS) and high-intensity interval (INT) exercise on reservoir function in well trained cyclists. METHODS: 20 competitive cyclists, M (n=14) and F (n=6), completed a high-intensity interval protocol consisting of 4 × 30 s high-intensity exercise bouts (Wingate tests) with 4.5 min active recovery between each bout. On a separate day, subjects completed an hour-long steady state cycling bout at 65% VO2 peak. VO2 peak was measured previously. The order of SS and INT exercise was randomized. Measurements were made at rest and 30 min post exercise. Aortic reservoir function was calculated as Diastolic Run-off (DR)/Stroke Volume (SV). DR was equal to Systemic Arterial Compliance (SAC) x End-Systolic Pressure (ESP)-Diastolic Pressure (DP). SAC was determined from Tau/TPR, and Tau was equal to diastolic time (DT)/ ln ESP-ln DP. All values were found 30 min post exercise. Statistical analysis was performed using ANOVAs with repeated measures (p<0.05). RESULTS: Average reservoir function at rest was 71%, which was significantly reduced to 51% (p<0.05) following SS exercise, but with a significantly greater reduction (from 67% to 33%, p<0.05) following INT exercise. DR was reduced significantly from 72 ml at rest to 48 ml following SS exercise (p<0.05) but the reduction in DR was significantly greater (p<0.05) post INT (from 65 ml to 28 ml). There were no significant changes in SAC following either SS or INT exercise. DT decreased significantly in both conditions but was significantly lower following INT exercise (858 ms to 680 ms 30 minutes post SS and 810 ms to 398 ms post INT; p<0.05). CONCLUSION: Aortic reservoir function is attenuated following acute SS and INT exercise, but these reductions were greater post INT suggesting that exercise intensity affects aortic reservoir function. These changes do not appear to be mediated by changes in SAC. The reduction in DT likely produced the lower aortic reservoir function, suggesting that reservoir function following exercise is primarily affected by heart rate and not by changes in arterial function per se.

Effects of pulsatile blood flow in large vessels on thermal dose distribution during thermal therapy

The aim of this study is to evaluate the effect of pulsatile blood flow in thermally significant blood vessels on the thermal lesion region during thermal therapy of tumor. A sinusoidally pulsatile velocity profile for blood flow was employed to simulate the cyclic effect of the heart beat on the blood flow. The evolution of temperature field was governed by the energy transport equation for blood flow together with Pennes' bioheat equation for perfused tissue encircling the blood vessel. The governing equations were numerically solved by a novel multi-block Chebyshev pseudospectral method and the accumulated thermal dose in tissue was computed. Numerical results show that pulsatile velocity profile, with various combinations of pulsatile amplitude and frequency, has little difference in effect on the thermal lesion region of tissue compared with uniform or parabolic velocity profile. However, some minor differences on the thermal lesion region of blood vessel is observed for middle-sized blood vessel. This consequence suggests that, in this kind of problem, we may as well do the simulation simply by a steady uniform velocity profile for blood flow.

Non-Newtonian effects of pulsatile blood flow in non-planar distal end-to-side anastomosis

Non-Newtonian effects of pulsatile blood flow in non-planar distal end-to-side anastomosis

Effects of oscillation on the arteries measured by arterial impedance during left ventricular assistance

Oscillating blood flow has effects on the arteries similar to the effects of pulsatile blood flow at lower frequencies. Alternating-current theory is useful to study the pulse in the circulatory system. Arterial impedance is a good index to estimate the frequency characteristics of the artery. In this study, total vascular resistance and arterial impedance were studied in animal experiments during left ventricular assistance. A centrifugal pump was used for comparison with a VFP (vibrating-flow pump). Left ventricular assistance was performed in animal experiments using goats. Total vascular resistance and arterial impedance were studied to estimate the frequency characteristics of the artery. Total vascular resistance during steady flow assistance decreased compared with that during nonassistance. Arterial walls were extended by the blood flow assistance at steady flow. The resistance during oscillating blood flow was different at each driving frequency, showing the frequency dependency, or pulse effect, of the arterial system under nonsteady flow. Arterial impedance was also studied during oscillating blood flow and showed a slight increase at a driving frequency of 25 or 30 Hz. These fluctuations in impedance are influenced by the reflection of the pulse. Arterial impedance should be taken into consideration when analyzing pulsatile blood flow because the pulse reflection may have some effects on the arterial wall. Some variation of blood pressure and blood flow might be necessary for stable support with artificial circulatory assistance.

A Higher Blood Flow Window of Reduced Thrombogenicity and Acceptable Fragmentation in a Hollow Fiber Hemodialyzer

The effect of pulsatile blood flow on platelet thrombogenicity and platelet fragmentation (PF) in a hollow fiber hemodialyzer (HFD) was quantified with 111In labeled platelets and 125I labeled fibrinogen; 150 ml of blood was collected from Beagle dogs, Yorkshire pigs, and a human volunteer (non-smoker). Platelets were labeled with 111In tropolone (300 microCi) and fibrinogen was labeled with 125I. Sham dialysis (SHD) was performed with 120 HFDs (0.9 meter2) at 37 degrees C, with flow-rates of 150, 250, 500, and 950 ml/min.; after SHD, the washed HD radioactivity was measured with an ionization chamber. PF was measured by flow cytometry with GP IIb-IIIa murine monoclonal antibody. Platelet deposition decreased significantly for 3 species at higher flow; fibrinogen deposition (10-12%, 55-65 mg/m2), was not affected by flow. Adherent platelet thrombus decreased from (8.2 +/- 3.4) to (3.1 +/- 1.0) with human blood as flow rate increased from 150 to 950 ml/min; platelet thrombus level also decreased significantly (p < 0.005) from (20.3 +/- 6.2) to (4.5 +/- 1.9) with canine blood. Higher values were obtained for canine than human and porcine platelets. Platelet fragmentation, on the other hand, increased from 2.1-2.2% to 10.2-11.3% with increase of flow. Like platelets, deposition of canine fibrinogen was slightly higher than that of pig and human. The studies of adherent thrombus and platelet fragmentation identified an important flow-window of reduced thrombogenicity and acceptable fragmentation, encouraging extracorporeal circulation at higher blood flow.

A new algorithm for deriving pulsatile blood flow waveforms tested using simulated dynamic angiographic data

In vascular pathology the assessment of disease severity and monitoring of treatment requires quantitative and reproducible measurements of arterial blood flow. We have developed a new technique for processing sequences of dynamic digital X-ray angiographic images. We have tested it using computer simulated angiographic data which includes the effect of pulsatile blood flow and X-ray quantum noise. A parametric image was formed in which the image grey-level represents dye concentration as a function of time and distance along a vessel segment. Adjacent concentration--distance profiles in the parametric image were re-registered along the vessel axis 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 is equal to the bolus velocity. We have tested several contrast medium injection methods including constant flow and a range of discrete pulses per second. The technique proved to be robust and independent of injection technique. Average blood flow was measured for simulated pulsatile waveforms with mean flows of up to 650 ml/min (peak velocities up to 186 cm/s) in a range of diameters from 2 mm to 6 mm. The standard deviation of the error in the mean flow estimates over the whole range of velocities and vessel sizes was +/- 1.4 cm/s.

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 ( τ ω ) 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).

Thromboxane and prostacyclin changes during cardiopulmonary bypass with and without pulsatile flow

Nonpulsatile cardiopulmonary bypass, in patients with coronary artery disease, produces a significant increase in thromboxane, a potent platelet aggregant and putative coronary vasoconstrictor. Pulsatile flow may decrease the incidence of perioperative infarction and the hormonal stress response to bypass. This study assessed the effect of pulsatile blood flow on plasma thromboxane and prostacyclin profiles during cardiopulmonary bypass by serial measurement of their stable metabolites, thromboxane B2 (TxB2) and 6-keto-prostaglandin F1 alpha (6-keto-PGF1 alpha). Two groups of eight patients each were studied before, during, and after cardiopulmonary bypass. Eight patients had routine (nonpulsatile) bypass and eight had pulsatile flow. In the nonpulsatile group, the TxB2 concentration significantly increased during bypass (65 +/- 39 to 1,224 +/- 306 pg/ml, p less than 0.01) and rapidly returned to control. Prostacyclin also rose (53 +/- 20 to 613 +/- 132 pg/ml, p less than 0.01). In the pulsatile group, TxB2 rose during bypass (53 +/- 18 to 693 +/- 130 pg/ml, p less than 0.01), but peak concentration was significantly lower than in the nonpulsatile group (1,224 +/- 306 versus 693 +/- 130 pg/ml, p less than 0.05). Prostacyclin rose sharply during cardiopulmonary bypass in the pulsatile group (53 +/- 22 to 1,033 +/- 136 pg/ml, p less than 0.01) and was higher than in the nonpulsatile group (1,033 +/- 136 versus 325 +/- 33 pg/ml, p less than 0.01). There were no intragroup differences of plasma hemoglobin, hematocrit, or platelet count. These data demonstrate that pulsatile flow significantly alters prostacyclin and thromboxane profiles during cardiopulmonary bypass and favors production of the coronary vasodilator and platelet disaggregant prostacyclin. This may be an important factor in some of the clinical advantages previously reported with this modality.

Patterns of sympathetic neuron activity associated with Mayer waves.

Patterns of sympathetic neuron activity associated with Mayer waves.