Showing papers on "Pulsatile flow published in 2015"
TL;DR: Nanocomposite in situ-gelling hydrogels containing both superparamagnetic iron oxide nanoparticles and thermoresponsive microgels are demonstrated to facilitate pulsatile, high-low release of a model drug.
Abstract: Nanocomposite in situ-gelling hydrogels containing both superparamagnetic iron oxide nanoparticles (SPIONs) and thermoresponsive microgels are demonstrated to facilitate pulsatile, high-low release of a model drug (4 kDa fluorescein-labeled dextran). The materials can be injected through a minimally invasive route, facilitate a ∼4-fold enhancement of release when pulsed on relative to the off state, and, in contrast to previous gel-based systems, can maintain pulsatile release properties over multiple cycles and multiple days instead of only hours. Optimal pulsatile release is achieved when the microgel transition temperature is engineered to lie just above the (physiological) incubation temperature. Coupled with the demonstrated degradability of the nanocomposites and the cytocompatibility of all nanocomposite components, we anticipate these nanocomposites have potential to facilitate physiologically relevant, controlled pulsatile drug delivery.
86 citations
TL;DR: CNS-wide simulations of intrathecal drugs administration can become a practical tool for in silico design, interspecies scaling and optimization of experimental drug trials, and the feasibility of computational drug transport studies was demonstrated.
78 citations
TL;DR: It is suggested that lack of pulsatility may be one factor that has limited the success of continuous flow LVADs and research needs to focus on methods to generate pulsatility either by the native heart or by various speed modulation algorithms.
Abstract: Despite significant improved survival with continuous flow left ventricular assist devices (LVADs), complications related to aortic valve insufficiency, gastrointestinal bleeding, stroke, pump thrombosis, and hemolysis have dampened the long term success of these pumps. Evolution has favored a pulsatile heart pump to be able to deliver the maximum flow at different levels of systemic vascular resistance, confer kinetic energy to the flow of blood past areas of stenosis and generate low shear stress on blood elements. In this perspective, we suggest that lack of pulsatility may be one factor that has limited the success of continuous flow LVADs and suggest that research needs to focus on methods to generate pulsatility either by the native heart or by various speed modulation algorithms.
77 citations
TL;DR: For both LV mass and the LV wall/LV cavity volume ratio, the loading sequence is an important determinant of LV response to arterial load.
Abstract: Arterial load is composed of resistive and various pulsatile components, but their relative contributions to left ventricular (LV) remodeling in the general population are unknown. We studied 4145 participants enrolled in the Multi-Ethnic Study of Atherosclerosis, who underwent cardiac MRI and radial arterial tonometry. We computed systemic vascular resistance (SVR=mean arterial pressure/cardiac output) and indices of pulsatile load including total arterial compliance (TAC, approximated as stroke volume/central pulse pressure), forward wave amplitude (Pf), and reflected wave amplitude (Pb). TAC and SVR were adjusted for body surface area to allow for appropriate sex comparisons. We performed allometric adjustment of LV mass for body size and sex and computed standardized regression coefficients (β) for each measure of arterial load. In multivariable regression models that adjusted for multiple confounders, SVR (β=0.08; P<0.001), TAC (β=0.44; P<0.001), Pb (β=0.73; P<0.001), and Pf (β=-0.23; P=0.001) were significant independent predictors of LV mass. Conversely, TAC (β=-0.43; P<0.001), SVR (β=0.22; P<0.001), and Pf (β=-0.18; P=0.004) were independently associated with the LV wall/LV cavity volume ratio. Women demonstrated greater pulsatile load than men, as evidenced by a lower indexed TAC (0.89 versus 1.04 mL/mm Hg per square meter; P<0.0001), whereas men demonstrated a higher indexed SVR (34.0 versus 32.8 Wood Units×m2; P<0.0001). In conclusion, various components of arterial load differentially associate with LV hypertrophy and concentric remodeling. Women demonstrated greater pulsatile load than men. For both LV mass and the LV wall/LV cavity volume ratio, the loading sequence (ie, early load versus late load) is an important determinant of LV response to arterial load.
71 citations
TL;DR: Among subjects with continuous-flow left ventricular assist devices, the restoration of pulsatile flow through modulations in pump speed leads to increased distortion of the arterial baroreceptors with a subsequent decline in MSNA.
Abstract: Background— Current-generation left ventricular assist devices provide circulatory support that is minimally or entirely nonpulsatile and are associated with marked increases in muscle sympathetic nerve activity (MSNA), likely through a baroreceptor-mediated pathway. We sought to determine whether the restoration of pulsatile flow through modulations in pump speed would reduce MSNA through the arterial baroreceptor reflex. Methods and Results— Ten men and 3 women (54±14 years) with Heartmate II continuous-flow left ventricular assist devices underwent hemodynamic and sympathetic neural assessment. Beat-to-beat blood pressure, carotid ultrasonography at the level of the arterial baroreceptors, and MSNA via microneurography were continuously recorded to determine steady-state responses to step changes (200–400 revolutions per minute) in continuous-flow left ventricular assist device pump speed from a maximum of 10 480±315 revolutions per minute to a minimum of 8500±380 revolutions per minute. Reductions in pump speed led to increases in pulse pressure (high versus low speed: 17±7 versus 26±12 mm Hg; P P P P =0.037). Conclusions— Among subjects with continuous-flow left ventricular assist devices, the restoration of pulsatile flow through modulations in pump speed leads to increased distortion of the arterial baroreceptors with a subsequent decline in MSNA. Additional study is needed to determine whether reduction of MSNA in this setting leads to improved outcomes.
68 citations
TL;DR: In this paper, the laminar flow of blood is taken to be incompressible and Newtonian fluid with variable viscosity depending upon temperature with an aim to provide resemblance to the real situation in the physiological system.
57 citations
02 Sep 2015
TL;DR: Theoretically, the use of the PWV ratio seems more logical for risk determination than aortic stiffness as it provides a better estimation of the loss of stiffness gradient, which is the unifying hypothesis that explains the impact of aorti stiffness both on the myocardium and on peripheral organs.
Abstract: Background: Aortic stiffness is a strong predictor of cardiovascular mortality in various clinical conditions. The aim of this review is to focus on the arterial stiffness gradient, to discuss the integrated role of medium-sized muscular conduit arteries in the regulation of pulsatile pressure and organ perfusion and to provide a rationale for integrating their mechanical properties into risk prediction. Summary: The physiological arterial stiffness gradient results from a higher degree of vascular stiffness as the distance from the heart increases, creating multiple reflective sites and attenuating the pulsatile nature of the forward pressure wave along the arterial tree down to the microcirculation. The stiffness gradient hypothesis simultaneously explains its physiological beneficial effects from both cardiac and peripheral microcirculatory points of view. The loss or reversal of stiffness gradient leads to the transmission of a highly pulsatile pressure wave into the microcirculation. This suggests that a higher degree of stiffness of medium-sized conduit arteries may play a role in protecting the microcirculation from a highly pulsatile forward pressure wave. Using the ratio of carotid-femoral pulse wave velocity (PWV) to carotid-radial PWV, referred to as PWV ratio, a recent study in a dialysis cohort has shown that the PWV ratio is a better predictor of mortality than the classical carotid-femoral PWV. Key Messages: Theoretically, the use of the PWV ratio seems more logical for risk determination than aortic stiffness as it provides a better estimation of the loss of stiffness gradient, which is the unifying hypothesis that explains the impact of aortic stiffness both on the myocardium and on peripheral organs.
53 citations
TL;DR: It is demonstrated that the alternative diagonal pump ECLS circuits appeared to have less systemic inflammatory response and hemolysis compared with the conventional roller pump E CLS circuit in simulated neonatal ECLs systems.
Abstract: The objective of this study was to compare the systemic inflammatory response and hemolytic characteristics of a conventional roller pump (HL20-NP) and an alternative diagonal pump with nonpulsatile (DP3-NP) and pulsatile mode (DP3-P) in simulated neonatal extracorporeal life support (ECLS) systems. The experimental neonatal ECLS circuits consist of a conventional Jostra HL20 roller pump or an alternative Medos DP3 diagonal pump, and Medos Hilite 800 LT hollow-fiber oxygenator with diffusion membrane. Eighteen sterile circuits were primed with freshly donated whole blood and divided into three groups: conventional HL20 with nonpulsatile flow (HL20-NP), DP3 with nonpulsatile flow (DP3-NP), and DP3 with pulsatile flow (DP3-P). All trials were conducted for durations of 12 h at a flow rate of 500 mL/min at 36°C. Simultaneous blood flow and pressure waveforms were recorded. Blood samples were collected to measure plasma-free hemoglobin (PFH), human tumor necrosis factor-alpha, interleukin-6 (IL-6), and IL-8, in addition to the routine blood gas, lactate dehydrogenase, and lactic acid levels. HL20-NP group had the highest PFH levels (mean ± standard error of the mean) after a 12-h ECLS run, but the difference among groups did not reach statistical significance (HL20-NP group: 907.6 ± 253.1 mg/L, DP3-NP group: 343.7 ± 163.2 mg/L, and DP3-P group: 407.6 ± 156.6 mg/L, P = 0.06). Although there were similar trends but no statistical differences for the levels of proinflammatory cytokines among the three groups, the HL20-NP group had much greater levels than the other groups (P > 0.05). Pulsatile flow generated higher total hemodynamic energy and surplus hemodynamic energy levels at pre-oxygenator and pre-clamp sites (P < 0.01). Our study demonstrated that the alternative diagonal pump ECLS circuits appeared to have less systemic inflammatory response and hemolysis compared with the conventional roller pump ECLS circuit in simulated neonatal ECLS systems. Pulsatile flow delivered more hemodynamic energy to the pseudo-patient without increased odds of hemolysis compared with the conventional, nonpulsatile roller pump group.
48 citations
TL;DR: It is demonstrated that non-Newtonian, blood-analog fluid rheology results in shear layer instabilities that alter the formation of vortical structures during the systolic deceleration and onwards during diastole.
Abstract: Complex, unsteady fluid flow phenomena in the arteries arise due to the pulsations of the heart that intermittently pumps the blood to the extremities of the body. The many different flow waveform variations observed throughout the arterial network are a result of this process and a function of the vessel properties. Large scale secondary flow structures are generated throughout the aortic arch and larger branches of the arteries. An experimental 180° curved artery test section with physiological inflow conditions was used to validate the computational methods implemented in this study. Good agreement of the secondary flow structures is obtained between experimental and numerical studies of a Newtonian blood-analog fluid under steady-state and pulsatile, carotid artery flow rate waveforms. Multiple vortical structures, some of opposite rotational sense to Dean vortices, similar to Lyne-type vortices, were observed to form during the systolic portion of the pulse. Computational tools were used to assess the effect of blood-analog fluid rheology (i.e., Newtonian versus non-Newtonian). It is demonstrated that non-Newtonian, blood-analog fluid rheology results in shear layer instabilities that alter the formation of vortical structures during the systolic deceleration and onwards during diastole. Additional vortices not observed in the Newtonian cases appear at the inside and outside of the bend at various times during the pulsation. The influence of blood-analog shear-thinning viscosity decreases mean pressure losses in contrast to the Newtonian blood analog fluid.
45 citations
TL;DR: An automated segmentation algorithm provides the first non-invasive method for determining ocular volume change due to pulsatile choroidal filling, and the estimation of the OR constant.
Abstract: We have developed a novel optical approach to determine pulsatile ocular volume changes using automated segmentation of the choroid, which, together with Dynamic Contour Tonometry (DCT) measurements of intraocular pressure (IOP), allows estimation of the ocular rigidity (OR) coefficient. Spectral Domain Optical Coherence Tomography (OCT) videos were acquired with Enhanced Depth Imaging (EDI) at 7Hz during ~50 seconds at the fundus. A novel segmentation algorithm based on graph search with an edge-probability weighting scheme was developed to measure choroidal thickness (CT) at each frame. Global ocular volume fluctuations were derived from frame-to-frame CT variations using an approximate eye model. Immediately after imaging, IOP and ocular pulse amplitude (OPA) were measured using DCT. OR was calculated from these peak pressure and volume changes. Our automated segmentation algorithm provides the first non-invasive method for determining ocular volume change due to pulsatile choroidal filling, and the estimation of the OR constant. Future applications of this method offer an important avenue to understanding the biomechanical basis of ocular pathophysiology.
45 citations
TL;DR: In this paper, the effect of aging on myogenic response of mouse MCAs was investigated and it was found that aging did not affect myogenic constriction in response to static increases in pressure, whereas it significantly impaired pulsatile pressure-induced myogenic tone.
Abstract: Stability of myogenic tone in middle cerebral arteries (MCA) is essential for adequate control over penetration of pressure waves into the distal portion of the cerebral microcirculation. Because the increased pulse pressure observed in advanced aging is associated with cerebromicrovascular injury, the effect of aging on myogenic response of mouse MCAs was determined. Aging did not affect the myogenic constriction in response to static increases in pressure, whereas it significantly impaired pulsatile pressure-induced myogenic tone. Impaired myogenic adaptation of MCAs to pulsatile pressure may allow high pressure to penetrate the distal portion of the cerebral microcirculation, contributing to microvascular damage.
TL;DR: A reversal of the normal arterial stiffness gradient is described, named stiffness mismatch, to enhance the transmission of pulsatile energy into the periphery and microcirculation and, theoretically, increase the risk for damage to microvascular beds in highly perfused organs.
Abstract: See related article, pp 378–384
Large arteries play an important role in converting flow oscillations—resulting from intermittent ventricular ejection—into continuous blood flow, along the arterial tree. These arteries can accommodate ≈50% of the stroke volume by distending their walls, with ≈10% of the energy produced by the heart being diverted to this distension and stored in the walls,1 and this ability is the result of a high elastin content in their arterial wall. However, the composition of the arterial wall changes from central to peripheral arteries, with a dominant collagen content in the peripheral arteries. Arteries become stiffer with increasing age and in different diseases (hypertension, chronic kidney disease [CKD], diabetes mellitus, or atherosclerosis), but this increase is more important in larger arteries than in the peripheral ones. In the peripheral arteries, there is even described a decrease in the stiffness of arterial wall, interpreted as an adaptation to an increased central aortic stiffness.2 This reversal of the normal arterial stiffness gradient, named stiffness mismatch, enhance the transmission of pulsatile energy into the periphery and microcirculation and, theoretically, increase the risk for damage to microvascular beds in highly perfused organs.
The carotid-femoral pulse wave velocity …
TL;DR: The investigation of time-averaged shear stress and the oscillatory shear index for 80% stenosis show that assuming laminar flow will cause more error than assuming a rigid wall, and the importance of assuming a flexible artery wall is more thanAssuming a rigid artery wall.
Abstract: The turbulent pulsatile blood flow through stenosed arteries considering the elastic property of the wall is investigated numerically. During the numerical model validation both standard k-e model and RNG K-e model are used. Compared with the RNG K-e model, the standard K-e model shows better agreement with previous experimental results and is better able to show the reverse flow region. Also, compared with experimental data, the results show that, up to 70% stenosis, the flow is laminar and for 80% stenosis the flow becomes turbulent. Assuming laminar or turbulent flow and also rigid or elastic walls, the results are compared with each other. The investigation of time-averaged shear stress and the oscillatory shear index for 80% stenosis show that assuming laminar flow will cause more error than assuming a rigid wall. The results also show that, in turbulent flow compared with laminar flow, the importance of assuming a flexible artery wall is more than assuming a rigid artery wall.
TL;DR: A unified method (Unified0D) for estimating loss coefficients that can be applied to any junction (i.e. any number of branches at any angle) and any flow regime is developed.
Abstract: In reduced-order (0D/1D) blood or respiratory flow models, pressure losses at junctions are usually neglected However, these may become important where velocities are high and significant flow redirection occurs Current methods for estimating losses rely on relatively complex empirical equations that are only valid for specific junction geometries and flow regimes In pulsatile multi-directional flows, switching between empirical equations upon reversing flow may introduce unrealistic discontinuities in simulated haemodynamic waveforms Drawing from work by Bassett et al (SAE Trans 112:565-583, 2003), we therefore developed a unified method (Unified0D) for estimating loss coefficients that can be applied to any junction (ie any number of branches at any angle) and any flow regime Discontinuities in simulated waveforms were avoided by extending Bassett et al's control volume-based method to incorporate a 'pseudodatum' supplier branch, an imaginary effective vessel containing all inflow to the junction Energy exchange between diverging flow streams was also accounted for empirically The formulation was validated using high resolution computational fluid dynamics in a wide range flow conditions and junction configurations In a pulsatile 1D simulation exhibiting transitions between four different flow regimes, the new formulation produced smooth transitions in calculated pressure losses
TL;DR: The dimensionless radial and axial velocity, volumetric flow rate, resistance impedance and wall shear stress are analyzed for normal and diseased artery with particular focus on variation of these quantities with non-Newtonian parameters.
Abstract: A two-dimensional model is used to analyze the unsteady pulsatile flow of blood through a tapered artery with stenosis The rheology of the flowing blood is captured by the constitutive equation of Carreau model The geometry of the time-variant stenosis has been used to carry out the present analysis The flow equations are set up under the assumption that the lumen radius is sufficiently smaller than the wavelength of the pulsatile pressure wave A radial coordinate transformation is employed to immobilize the effect of the vessel wall The resulting partial differential equations along with the boundary and initial conditions are solved using finite difference method The dimensionless radial and axial velocity, volumetric flow rate, resistance impedance and wall shear stress are analyzed for normal and diseased artery with particular focus on variation of these quantities with non-Newtonian parameters
TL;DR: Comparing the range of blood flow parameters in ascending aorta that can result from various angulations of outflow graft anastomosis of a left ventricular assist device (LVAD) to the aortic wall is quantified as a means to understand the mechanism of aortIC valve insufficiency.
TL;DR: The findings suggest that ECG-triggered pulsatile ECLS provides superior end-organ protection with improved renal function and systemic vascular tone.
Abstract: The primary objective of this study was to evaluate a novel electrocardiogram (ECG)-synchronized pulsatile extracorporeal life support (ECLS) system for adult partial mechanical circulatory support for adequate quality of pulsatility and enhanced hemodynamic energy generation in an in vivo animal model. The secondary aim was to assess end-organ protection during nonpulsatile versus synchronized pulsatile flow mode. Ten adult swine were randomly divided into a nonpulsatile group (NP, n = 5) and pulsatile group (P, n = 5), and placed on ECLS for 24 h using an i-cor system consisting of an i-cor diagonal pump, an iLA membrane ventilator, an 18 Fr femoral arterial cannula and a 23/25 Fr femoral venous cannula. Trials were conducted at a flow rate of 2.5 L/min using nonpulsatile or pulsatile mode (with assist ratio 1:1). Real-time pressure and flow data were recorded using a custom-based data acquisition system. To the best of our knowledge, the oxygenator and circuit pressure drops were the lowest for any available system in both groups. The ECG-synchronized i-cor ECLS system was able to trigger pulsatile flow in the porcine model. After 24-h ECLS, energy equivalent pressure, surplus hemodynamic energy, and total hemodynamic energy at preoxygenator and prearterial cannula sites were significantly higher in the P group than those in the NP group (P 0.05). The novel i-cor system performed well in the nonpulsatile and ECG-synchronized pulsatile mode in an adult animal ECLS model. The iLA membrane oxygenator had an extremely lower transmembrane pressure gradient and excellent gas exchange capability. Our findings suggest that ECG-triggered pulsatile ECLS provides superior end-organ protection with improved renal function and systemic vascular tone.
TL;DR: Changes in axial length and the possible influence of these changes on the physical properties of choroidal vessels is the mechanism believed to be responsible for putting high myopes at risk for ocular vascular diseases.
Abstract: Pulsatile ocular blood flow (POBF) determines the summed volume of blood entering the outer retina, choroid, and remaining uveal tract of the eye by measuring increases in intraocular pressure (IOP), with each heartbeat. POBF reflects the choroidal circulation, which is responsible for 85% of the POBF [1]. Other pulsatile components of pulse amplitude (OBFa), pulse volume (OBFv), and pulse rate (OBFr). OBFa indicates the amplitude of blood flow entering the eyeball. OBFv indicates the amount of blood entering the eyeball per each contraction of the heart. OBFr indicates the rate of ocular blood flow due to hear beat. This noninvasive assessment of ocular blood flow is based on analysis of the IOP pulse quantified by Perkins [2], utilizing a modified applanation prism with distensible film at the contact surface. Langham et al. [1] used a pneumotonometer to obtain a wave form of the ocular pulse, and subsequently derived values for POBF by assessing this wave form and its amplitude, together with the heart rate of subject. The pulsatile components of choroidal circulation are calculated from the ocular pulse wave produced by the bolus of blood entering the eye during cardiac systole. Because the eye is a closed compartment, volumetric blood changes are transferred to a pressure gradient, which is recorded by the pneumotonometer and linked to a blood flow analyzer (BFA). Measurements of POBF using this system have been found to give reproducible results [3,4]. Thus, POBF analysis is used for assessment of ocular vascular pathologies.
POBF has been evaluated in several ocular diseases, including glaucoma, retinitis pigmentosa, and age related macular degeneration [5,6,7]. Several authors have reported that factors such as age, heart rate, blood pressure, and axial length influence POBF [8,9,10,11]. Previous studies have reported that a relationship exists between the refractive error or axial length of the eye and POBF [11,12,13]. A study by Mori et al. [12] shows no correlation of refractive error with POBF, while a study by Benavente-Perez et al. [13] shows a positive correlation of refractive error with POBF.
In this study, we evaluate the pulsatile components of ocular blood flow (OBFa, OBFv, OBFr, and POBF) in healthy young human eyes, and determine choroidal blood flow changes in eyes with high myopia according to the pulsatile components of ocular blood flow analysis.
TL;DR: It can be observed that stenoses in an artery significantly influence the haemodynamic parameters of wall shear stress and pressure drop in contrast to dilatations case, deduces that stenosis plays a more critical role in plaque growth and vulnerability in contrastto dilatation, and should be the key element in cardiovascular pathology and diagnosis.
Abstract: In this paper, we have analysed pulsatile flow through partially occluded elastic arteries, to determine the haemodynamic parameters of wall shear stress (WSS), wall pressure gradient and pressure drops (ΔP), contributing to enhanced flow resistance and myocardial ischaemic regions which impair cardiac contractility and cause increased work load on the heart. In summary, it can be observed that stenoses in an artery significantly influence the haemodynamic parameters of wall shear stress and pressure drop in contrast to dilatations case. This deduces that stenosis plays a more critical role in plaque growth and vulnerability in contrast to dilatation, and should be the key element in cardiovascular pathology and diagnosis. Through quantitative analysis of WSS and ΔP, we have provided a clearer insight into the haemodynamics of atherosclerotic arteries. Determination of these parameters can be helpful to cardiologists, because it is directly implicated in the genesis and development of atherosclerosis.
TL;DR: Blood flow imparts a dynamic continuum from vascular development to repair andAugmentation of PSS confers atheroprotection and reactivation of developmental signalling pathways for regeneration.
Abstract: Purpose of review: Blood flow is intimately linked with cardiovascular development, repair and dysfunction. The current review will build on the fluid mechanical principle underlying haemodynamic shear forces, mechanotransduction and metabolic effects.
Recent findings: Pulsatile flow produces both time (∂τ/∂t) and spatial-varying shear stress (∂τ/∂x) to modulate vascular oxidative stress and inflammatory response with pathophysiological significance to atherosclerosis. The characteristics of haemodynamic shear forces, namely, steady laminar (∂τ/∂t = 0), pulsatile shear stress (PSS: unidirectional forward flow) and oscillatory shear stress (bidirectional with a near net 0 forward flow), modulate mechano-signal transduction to influence metabolic effects on vascular endothelial function. Atheroprotective PSS promotes antioxidant, anti-inflammatory and antithrombotic responses, whereas atherogenic oscillatory shear stress induces nicotinamide adenine dinucleotide phosphate oxidase–JNK signalling to increase mitochondrial superoxide production, protein degradation of manganese superoxide dismutase and post-translational protein modifications of LDL particles in the disturbed flow-exposed regions of vasculature. In the era of tissue regeneration, shear stress has been implicated in reactivation of developmental genes, namely, Wnt and Notch signalling, for vascular development and repair.
Summary: Blood flow imparts a dynamic continuum from vascular development to repair. Augmentation of PSS confers atheroprotection and reactivation of developmental signalling pathways for regeneration.
TL;DR: The contribution of pulsatility by the native heart may induce a periodic disturbance to an otherwise stable flow field within an axial flow ventricular assist device, particularly during the diastolic and decelerating portion of the cardiac cycle.
TL;DR: The results suggest that the Newtonian approximation can accurately model wall shear stress in the aortic flow of blood; however, for other variables (e.g. mean velocity) the shear-thinning model is more appropriate.
Abstract: The effects of percentage stenosis and Reynolds number (Re) on steady flow, and Womersley number (Wo) on pulsatile flow, of blood through a two-dimensional channel with stenosis are investigated, and the results are compared with the Newtonian case. We model blood using the shear-thinning relation proposed by Yeleswarapu, while the stenosis is approximated using a cosine-shaped taper. The vorticity–streamfunction formulation of the flow equations is solved using a finite difference scheme in conjunction with a full-multigrid algorithm that reduces computational time. The presence of stenosis leads to a recirculation zone immediately downstream of the stenosis. In steady flow, the shear-thinning fluid predicts higher peak wall shear stress than the Newtonian fluid: the difference between the predictions, expressed as a percentage of the Newtonian wall shear stress, decreases as percentage stenosis and Reynolds number increase. For a given percentage stenosis and Reynolds number, the percentage difference between the shear-thinning fluid and Newtonian fluid decreases, and remains negligible, as the Womersley number increases (corresponding to increasing pulsatile nature of the flow). This suggests that the Newtonian approximation can accurately model wall shear stress in the aortic flow of blood; however, for other variables (e.g. mean velocity) the shear-thinning model is more appropriate.
TL;DR: In this article, a mathematical model for two-dimensional pulsatile blood flow through overlapping constricted tapered vessels is presented, where an improved shape of the time-variant overlapping stenosis in the elastic tapered artery subject to pulsatile pressure gradient is considered.
Abstract: In this study a mathematical model for two-dimensional pulsatile blood flow through overlapping constricted tapered vessels is presented. In order to establish resemblance to the in vivo conditions, an improved shape of the time-variant overlapping stenosis in the elastic tapered artery subject to pulsatile pressure gradient is considered. Because it contains a suspension of all erythrocytes, the flowing blood is represented by micropolar fluid. By applying a suitable coordinate transformation, tapered cosine-shaped artery turned into non-tapered rectangular and a rigid artery. The governing nonlinear partial differential equations under the imposed realistic boundary conditions are solved using the finite difference method. The effects of vessel tapering on flow characteristics considering their dependencies with time are investigated. The results show that by increasing the taper angle the axial velocity and volumetric flow rate increase and the microrotational velocity and resistive impedance reduce. It has been shown that the results are in agreement with similar data from the literature.
TL;DR: Depending on the pulsatility setting, i-cor ECLS system generates physiological quality pulsatile flow without increasing the mean circuit pressure and energy loss depending on the circuit components was almost similar in both perfusion modes at all different flow rates.
Abstract: The objective of this study is to investigate the impact of every component of extracorporeal life support (ECLS) circuit on hemodynamic energy transmission in terms of energy equivalent pressure (EEP), total hemodynamic energy (THE), and surplus hemodynamic energy (SHE) under nonpulsatile and pulsatile modes in a novel ECLS system. The ECLS circuit consisted of i-cor diagonal pump and console (Xenios AG, Heilbronn, Germany), an iLA membrane ventilator (Xenios AG), an 18 Fr femoral arterial cannula, a 23/25 Fr femoral venous cannula, and 3/8-in ID arterial and venous tubing. The circuit was primed with lactated Ringer's solution and human whole blood (hematocrit 33%). All trials were conducted under room temperature at the flow rates of 1–4 L/min (1 L/min increments). The pulsatile flow settings were set at pulsatile frequency of 75 beats per minute and differential speed values of 1000–4000 rpm (1000 rpm increments). Flow and pressure data were collected using a custom-based data acquisition system. EEP was significantly higher than mean arterial pressure in all experimental conditions under pulsatile flow (P < 0.01). THE was also increased under pulsatile flow compared with the nonpulsatile flow (P < 0.01). Under pulsatile flow conditions, SHE was significantly higher and increased differential rpm resulted in significantly higher SHE (P < 0.01). There was no SHE generated under nonpulsatile flow. Energy loss depending on the circuit components was almost similar in both perfusion modes at all different flow rates. The pressure drops across the oxygenator were 3.8–24.9 mm Hg, and the pressure drops across the arterial cannula were 19.3–172.6 mm Hg at the flow rates of 1–4 L/min. Depending on the pulsatility setting, i-cor ECLS system generates physiological quality pulsatile flow without increasing the mean circuit pressure. The iLA membrane ventilator is a low-resistance oxygenator, and allows more hemodynamic energy to be delivered to the patient under pulsatile mode. The 18 Fr femoral arterial cannula has acceptable pressure drops under nonpulsatile and pulsatile modes. Further in vivo studies are warranted to confirm these results.
TL;DR: In this article, the geometry and operating conditions of a micromixer with convergent-divergent sinusoidal walls under pulsatile flow were optimized to maximize the mixing performance.
TL;DR: Inaccuracy of conventional four‐dimensional flow MR imaging in the presence of random unsteady and turbulent blood flow distal to a narrowing is challenged and shorter echo times decrease the errors, leading to more accurate flow assessments.
Abstract: Purpose
Inaccuracy of conventional four-dimensional (4D) flow MR imaging in the presence of random unsteady and turbulent blood flow distal to a narrowing has been an important challenge. Previous investigations have revealed that shorter echo times (TE) decrease the errors, leading to more accurate flow assessments.
Methods
In this study, as part of a 4D flow acquisition, an Ultra-Short TE (UTE) method was adopted. UTE works based on a center-out radial k-space trajectory that inherently has a short TE. By employing free induction decay sampling starting from read-out gradient ramp-up, and by combining the refocusing lobe of the slice select gradient with the bipolar flow encoding gradient, TEs of ≈1 msec may be achieved.
Results
Both steady and pulsatile flow regimes, and in each case a range of Reynolds numbers, were studied in an in-vitro model. Flow assessment at low and medium flow rates demonstrated a good agreement between 4D UTE and conventional 4D flow techniques. However, 4D UTE flow significantly outperformed conventional 4D flow, at high flow rates for both steady and pulsatile flow regimes. Feasibility of the method in one patient with Aortic Stenosis was also demonstrated.
Conclusion
For both steady and pulsatile high flow rates, the measured flow distal to the stenotic narrowing using conventional 4D flow revealed more than 20% error compared to the ground-truth flow. This error was reduced to less than 5% using the 4D UTE flow technique. Magn Reson Med 73:939–950, 2015. © 2014 Wiley Periodicals, Inc.
TL;DR: In this study, organ damage was significantly attenuated as compared with non-pulsatile CPB and in pediatric patients pulsatileCPB may improve clinical outcomes.
TL;DR: Computational assessment of coronary pressure is feasible and seems to be accurate compared to the wire-based measurements, and the results showed a high correlation between the measured and the computed coronary pressure values.
Abstract: Pressure measurements using finite element computations without the need of a wire could be valuable in clinical practice. Our aim was to compare the computed distal coronary pressure values with the measured values using a pressure wire, while testing the effect of different boundary conditions for the simulation. Eight coronary arteries (lumen and outer vessel wall) from six patients were reconstructed in three-dimensional (3D) space using intravascular ultrasound and biplane angiographic images. Pressure values at the distal and proximal end of the vessel and flow velocity values at the distal end were acquired with the use of a combo pressure-flow wire. The 3D lumen and wall models were discretized into finite elements; fluid structure interaction (FSI) and rigid wall simulations were performed for one cardiac cycle both with pulsatile and steady flow in separate simulations. The results showed a high correlation between the measured and the computed coronary pressure values (coefficient of determination [r2] ranging between 0.8902 and 0.9961), while the less demanding simulations using steady flow and rigid walls resulted in very small relative error. Our study demonstrates that computational assessment of coronary pressure is feasible and seems to be accurate compared to the wire-based measurements.
TL;DR: It is concluded that exposure to substantially increased flow is required to initiate angiogenesis in grafted veins, whereas selective enhancement of pulsatile flow is unable to do so.
Abstract: Exposing a vein to altered hemodynamics by creating an arteriovenous (AV) shunt evokes considerable vessel formation that may be of therapeutic potential. However, it is unclear whether the introduction of oscillatory flow and/or flow increase is decisive. To distinguish between these mechanical stimuli we grafted a femoral vein into the arterial flow pathway of the contralateral limb in rats creating an arterioarterial (AA) loop (n = 7). Alternatively, we connected the femoral artery and vein using the vein graft, whereby we created an AV-loop (n = 27). Vessel loops were embedded in a fibrin filled chamber and blood flow was measured by means of flow probes immediately after surgery (day 0) and 15 days after loop creation. On day 15, animals were sacrificed and angiogenesis was evaluated using μCT and histological analysis. Mean flow increased from 0.5 to 2.4 mL/min and was elevated throughout the cardiac cycle at day 0 in AV-loops whereas, as expected, it remained unchanged in AA-loops. Flow in AV-loops decreased with time, and was at day 15 not different from untreated femoral vessels or AA-loop grafts. Pulsatile flow oscillations were similar in AV-and AA-loops at day 0. The flow amplitude amounted to ~1.3 mL/min which was comparable to values in untreated arteries. Flow amplitude remained constant in AA-loops, whereas it decreased in AV-loops (day 15: 0.4 mL/min). A large number of newly formed vessels were present in AV-loops at day 15 arising from the grafted vein. In marked contrast, angiogenesis originating from the grafted vein was absent in AA-loops. We conclude that exposure to substantially increased flow is required to initiate angiogenesis in grafted veins, whereas selective enhancement of pulsatile flow is unable to do so. This suggests that indeed flow and most likely wall shear stress is decisive to initiate formation of vessels in this hemodynamically driven angiogenesis model.
TL;DR: Percutaneous cardiac support using a venoarterial cardiac assist device equipped with a novel diagonal pump is able to restore and increase systemic and coronary circulation during ventricular fibrillation and Electrocardiographically triggered synchronized cardiac assist provides an additional increase of coronary artery flow.
Abstract: Patients with cardiogenic shock have a very high mortality. Here we report the first use of a percutaneous pulsatile cardiac assist device, based on a diagonal pump synchronized with the heart cycle by means of an electrocardiographic signal in adult pigs. Eight domestic pigs underwent mandatory ventilation. During sinus rhythm, there were no differences between pulsatile and nonpulsatile perfusion with regard to pulmonary artery pressure, pulmonary wedge pressure, central venous pressure, mean arterial pressure (MAP), mean pulse pressure, and mean coronary artery flow (CAF). After 2 min of complete cardiac arrest (ventricular fibrillation), circulatory support with the i-cor in venoarterial nonpulsatile extracorporeal membrane oxygenation (ECMO) mode (3 L/min) restored systemic circulation, with an increase of MAP to 78.3 mm Hg and CAF to 5.27 mL/min. After changing from ECMO settings to pulsatile mode (3 L/min, 75 bpm, pulse amplitude range 3500 rpm), MAP did not change significantly (75.6 mm Hg); however, CAF increased to 8.45 mL/min. After changing back to nonpulsatile mode, MAP remained stable (83.6 mm Hg), but CAF decreased to 4.85 mL/min. Thereafter, pulsatile cardiac assist was established with a reduced blood flow of 2.5 L/min, and the pulse amplitude range was extended to 4500 rpm. Under these conditions, MAP remained stable (71.0 mm Hg), but CAF significantly increased to 15.2 mL/min (P < 0.05). Percutaneous cardiac support using a venoarterial cardiac assist device equipped with a novel diagonal pump is able to restore and increase systemic and coronary circulation during ventricular fibrillation. Electrocardiographically triggered synchronized cardiac assist provides an additional increase of coronary artery flow. These promising results are to be confirmed in humans.