Showing papers on "Pulsatile flow published in 2017"
TL;DR: In this article, a compliant, three-dimensional co-culture model of the blood-brain barrier was used to demonstrate that mechanical stimuli exerted by blood flow mediate both the permeability of the endothelial barrier and waste transport along the basement membrane.
124 citations
01 Apr 2017
TL;DR: Assessment of pulsatile arterial haemodynamics and time-resolved myocardial wall stress provide critical incremental physiological information and should be more widely utilised in heart failure.
Abstract: Measures of interaction between the left ventricle (LV) and arterial system (ventricular-arterial coupling) are important but under-recognised cardiovascular phenotypes in heart failure. Ventriculo-arterial coupling is commonly assessed in the pressure-volume plane, using the ratio of effective arterial elastance (EA) to LV end-systolic elastance (EES) to provide information on ventricular-arterial system mechanical efficiency and performance when LV ejection fraction is abnormal. These analyses have significant limitations, such as neglecting systolic loading sequence, and are less informative in heart failure with preserved ejection fraction (HFpEF). EA is almost entirely dependent on vascular resistance and heart rate. Assessment of pulsatile arterial haemodynamics and time-resolved myocardial wall stress provide critical incremental physiological information and should be more widely utilised. Pulsatile arterial load represents a promising therapeutic target in HFpEF. Here, we review various approaches to assess ventricular-arterial interactions, and their pathophysiological and clinical implications in heart failure.
64 citations
TL;DR: The present study inspects novelties brought about into the classic peristaltic mechanism by the inclusion of Womersley number, and the critical values of concentration and occlusion on the flow characteristics in a small artery with flexible walls.
Abstract: This work is concerned with theoretically investigating the pulsatile flow of a fluid with suspended particles in a flow driven by peristaltic waves that deform the wall of a small blood artery in the shape of traveling sinusoidal waves with constant velocity. The problem formulation in the wave frame of reference is presented and the governing equations are developed up to the second-order in terms of the asymptotic expansion of Womersley number which characterizes the unsteady effect in the wave frame. We suppose that the flow rate imposed, in this frame, is a function versus time. The analytical solution of the problem is achieved using the long wavelength approximation where Reynolds number is considered small with reference to the blood flow in the circulatory system. The present study inspects novelties brought about into the classic peristaltic mechanism by the inclusion of Womersley number, and the critical values of concentration and occlusion on the flow characteristics in a small artery with flexible walls. Momentum and mass equations for the fluid and particle phases are solved by means of a perturbation analysis in which the occlusion is a small parameter. Closed form solutions are obtained for the fluid/particle velocity distributions, stream function, pressure rise, friction force, wall shear stress, instantaneous mechanical efficiency, and time-averaged mechanical efficiency. The physical explanation of the Segre–Silberberg effect is introduced and the trapping phenomenon of plasma for haemodilution and haemoconcentration cases is discussed. It has been deduced that the width of the closed plasma streamlines is increased while their number is minimally reduced in case of haemoconcentration. This mathematical problem has numerous applications in various branches in science including blood flow in small blood vessels. Several results of other models can be deduced as limiting cases of our situation.
59 citations
TL;DR: In this study, 4D flow MRI was used to measure intra-cranial flow features with cardiac-gated phase contrast MRI in cranial arteries and veins in subjects with Alzheimer’s disease and age-matched controls.
Abstract: Cerebral blood flow, arterial pulsation, and vasomotion may be important indicators of cerebrovascular health in aging and diseases of aging such as Alzheimer's disease. Noninvasive markers that assess these characteristics may be helpful in the study of co-occurrence of these diseases and potential additive and interacting effects. In this study, 4D flow MRI was used to measure intra-cranial flow features with cardiac-gated phase contrast MRI in cranial arteries and veins. Mean blood flow and pulsatility index as well as the transit time of the peak flow from the middle cerebral artery to the superior sagittal sinus were measured in a total of 104 subjects comprising of four groups: (a) subjects with Alzheimer's disease, (b) age-matched controls, (c) subjects with mild cognitive impairment, and (d) a group of late middle-aged with parental history of sporadic Alzheimer's disease. The Alzheimer's disease group exhibited: a significant decrease in mean blood flow in the superior sagittal sinus, transverse sinus, middle cerebral artery, and internal carotid arteries; a significant decrease of the peak and end diastolic blood flow in the middle cerebral artery and superior sagittal sinus; a faster transmission of peak flow from the middle cerebral artery to the superior sagittal sinus and increased pulsatility index along the carotid siphon.
55 citations
TL;DR: The results clearly demonstrate the flow pattern and flow stagnation in the sinus is sensitive to THV position, and it is important for the interventional cardiologist and cardiac surgeon to consider how deployment position could impact flow stagnation during VIV-TAVR.
Abstract: Valve-in-valve transcatheter aortic valve replacement (VIV-TAVR) has proven to be a successful treatment for high risk patients with failing aortic surgical bioprostheses. However, thrombus formation on the leaflets of the valve has emerged as a major issue in such procedures, posing a risk of restenosis, thromboembolism, and reduced durability. In this work we attempted to understand the effect of deployment position of the transcatheter heart valve (THV) on the spatio-temporal flow field within the sinus in VIV-TAVR. Experiments were performed in an in vitro pulsatile left heart simulator using high-speed Particle Image Velocimetry (PIV) to measure the flow field in the sinus region. The time-resolved velocity data was used to understand the qualitative and quantitative flow patterns. In addition, a particle tracking technique was used to evaluate relative thrombosis risk via sinus washout. The velocity data demonstrate that implantation position directly affects sinus flow patterns, leading to increased flow stagnation with increasing deployment height. The particle tracking simulations showed that implantation position directly affected washout time, with the highest implantation resulting in the least washout. These results clearly demonstrate the flow pattern and flow stagnation in the sinus is sensitive to THV position. It is, therefore, important for the interventional cardiologist and cardiac surgeon to consider how deployment position could impact flow stagnation during VIV-TAVR.
42 citations
TL;DR: It is demonstrated for the first time that the JVP can be consistently observed in a non-contact manner using a photoplethysmographic imaging system and the observed jugular waveform was strongly negatively correlated to the arterial waveform.
Abstract: Cardiovascular monitoring is important to prevent diseases from progressing. The jugular venous pulse (JVP) waveform offers important clinical information about cardiac health, but is not routinely examined due to its invasive catheterisation procedure. Here, we demonstrate for the first time that the JVP can be consistently observed in a non-contact manner using a photoplethysmographic imaging system. The observed jugular waveform was strongly negatively correlated to the arterial waveform (r = −0.73 ± 0.17), consistent with ultrasound findings. Pulsatile venous flow was observed over a spatially cohesive region of the neck. Critical inflection points (c, x, v, y waves) of the JVP were observed across all participants. The anatomical locations of the strongest pulsatile venous flow were consistent with major venous pathways identified through ultrasound.
41 citations
TL;DR: In this paper, a pulsatile micromixer is presented, which does not use any dynamic off-chip controllers to achieve homogeneous mixing and shows homogenous mixing with a mixing index of ∼90% for a flow rate of up to 20μL/min and switching frequency in the range of 14-20 Hz.
40 citations
TL;DR: In this article, the authors conducted a numerical study via ADINA 8.8 software on the non-Newtonian pulsatile flow of blood through an elastic blood artery with single and consecutive stenosis.
Abstract: Atherosclerosis develops due to different hemodynamic factors, among which time-averaged Wall shear stress (mean WSS) and Oscillatory shear index (OSI) are two of the most important. These two factors not only depend on flow geometry, but are also influenced by rheological characteristics of blood. Since analytical solutions are limited to simple problems and since experimental tests are costly and time consuming, CFD solutions been prominently and effectively used to solve such problems. We conducted a numerical study via ADINA 8.8 software on the non-Newtonian pulsatile flow of blood through an elastic blood artery with single and consecutive stenosis. The studied stenosis cross sectional area was 70 % that of the unstenosed artery. The single stenosis results were compared with the consecutive stenosis results. The five non-Newtonian flow models, the Carreau model, the Carreau-Yasuda model, the modified Casson model, the power-law model, and the generalized power-law model, were used to model the non-Newtonian blood flow. The obtained results showed that increasing the number of stenoses would lead to reduced length of the oscillatory area after the first stenosis, thus forming another oscillatory area with a larger length after the second stenosis. Thus, a consecutive stenosis would develop a larger disease prone area. Upon examining the mean WSS and OSI, we found that, as compared with the other models, the modified Casson model and the power-law model produced predictions for the most extent of damage to endothelial cells and the most disease prone areas, respectively.
39 citations
TL;DR: Calculations reveal that velocity, flow rate and shear stress increase while resistance to flow decreases with greater permeability parameter, indicating that progressively more porous media avoid bolus growth.
38 citations
TL;DR: In this article, the deformation of a thin, elastic splitter plate attached to the rear of a circular cylinder and subjected to laminar pulsatile inflow is investigated.
31 citations
Journal Article•
TL;DR: It is concluded that the non-Newtonian flow model for blood has to be considered for the flow simulation in aorta of normal subject based on the results of CFD simulations of pulsatile blood flow.
Abstract: Pulsatile blood flow in an aorta of normal subject is studied by Computational Fluid Dynamics (CFD) simulations. The main intention of this study is to determine the influence of the non-Newtonian nature of blood on a pulsatile flow through an aorta. The usual Newtonian model of blood viscosity and a non- Newtonian blood model are used to study the velocity distributions, wall pressure and wall shear stress in the aorta over the entire cardiac cycle. Realistic boundary conditions are applied at various branches of the aorta model. The difference between non-Newtonian and Newtonian blood flow models is investigated at four different time instants in the fifth cardiac cycle. This study revealed that, the overall velocity distributions and wall pressure distributions of the aorta for a non-Newtonian fluid model are similar to the same obtained from Newtonian fluid model but the non-Newtonian nature of blood caused a considerable increase in Wall Shear Stress (WSS) value. The maximum wall shear stress value in the aorta for Newtonian fluid model was 241.706 Pa and for non-Newtonian fluid model was 249.827 Pa. Based on the results; it is observed that the non-Newtonian nature of blood affects WSS value. Therefore, it is concluded that the non-Newtonian flow model for blood has to be considered for the flow simulation in aorta of normal subject.
TL;DR: Assessment of pulse pressure gradient at level C2 was not found feasible to replace invasive monitoring of pulsatile intracranial pressure in selection of patients with idiopathic normal pressure hydrocephalus for surgical shunting, because of complexity of cervical cerebrospinal fluid flow and -pulsatility at the upper cervical spinal canal.
Abstract: Invasive monitoring of pulsatile intracranial pressure can accurately predict shunt response in patients with idiopathic normal pressure hydrocephalus, but may potentially cause complications such as bleeding and infection. We tested how a proposed surrogate parameter for pulsatile intracranial pressure, the phase-contrast magnetic resonance imaging derived pulse pressure gradient, compared with its invasive counterpart. In 22 patients with suspected idiopathic normal pressure hydrocephalus, preceding invasive intracranial pressure monitoring, and any surgical shunt procedure, we calculated the pulse pressure gradient from phase-contrast magnetic resonance imaging derived cerebrospinal fluid flow velocities obtained at the upper cervical spinal canal using a simplified Navier-Stokes equation. Repeated measurements of the pulse pressure gradient were also undertaken in four healthy controls. Of 17 shunted patients, 16 responded, indicating high proportion of "true" normal pressure hydrocephalus in the patient cohort. However, there was no correlation between the magnetic resonance imaging derived pulse pressure gradient and pulsatile intracranial pressure (R = -.18, P = .43). Pulse pressure gradients were also similar in patients and healthy controls (P = .26), and did not differ between individuals with pulsatile intracranial pressure above or below established thresholds for shunt treatment (P = .97). Assessment of pulse pressure gradient at level C2 was therefore not found feasible to replace invasive monitoring of pulsatile intracranial pressure in selection of patients with idiopathic normal pressure hydrocephalus for surgical shunting. Unlike invasive, overnight monitoring, the pulse pressure gradient from magnetic resonance imaging comprises short-term pressure fluctuations only. Moreover, complexity of cervical cerebrospinal fluid flow and -pulsatility at the upper cervical spinal canal may render the pulse pressure gradient a poor surrogate marker for intracranial pressure pulsations.
TL;DR: Comparisons between 3D patient-specific CFD simulations using both the time-averaged and pulsatile BCs for 101 Fontan patients reveal that HFD sensitivity is significantly different between single and bilateral superior vena cava cohorts but no other demographic discrepancies were observed for HFD or iPL.
TL;DR: The mechanism of self-regulation functioned properly, continuously throughout the chronic in vivo experiments, demonstrating the performance goals and demonstrating a totally self-regulating mode of operation.
Abstract: Cleveland Clinic's continuous-flow total artificial heart (CFTAH) provides systemic and pulmonary circulations using one assembly (one motor, two impellers). The right pump hydraulic output to the pulmonary circulation is self-regulated by the rotating assembly's passive axial movement in response to atrial differential pressure to balance itself to the left pump output. This combination of features integrates a biocompatible, pressure-balancing regulator with a double-ended pump. The CFTAH requires no flow or pressure sensors. The only control parameter is pump speed, modulated at programmable rates (60-120 beats/min) and amplitudes (0 to ±25%) to provide flow pulses. In bench studies, passive self-regulation (range: -5 mm Hg ≤ [left atrial pressure - right atrial pressure] ≤ 10 mm Hg) was demonstrated over a systemic/vascular resistance ratio range of 2.0-20 and a flow range of 3-9 L/min. Performance of the most recent pump configuration was demonstrated in chronic studies, including three consecutive long-term experiments (30, 90, and 90 days). These experiments were performed at a constant postoperative mean speed with a ±15% speed modulation, demonstrating a totally self-regulating mode of operation, from 3 days after implant to explant, despite a weight gain of up to 40%. The mechanism of self-regulation functioned properly, continuously throughout the chronic in vivo experiments, demonstrating the performance goals.
TL;DR: In this paper, the authors examined the motion of magnetic-nanoparticles and the flow characteristics of biofluid in a micro-tube in the presence of externally applied magnetic field and electrokinetic effects.
TL;DR: TO with the present setup, is not interchangeable with PACTD for cardiac volume flow estimation, but is a reliable and precise angle-independent ultrasound alternative for velocity estimation of cardiac flow.
TL;DR: Results corroborate clinical experience that continuous flow VADs produce higher CO and superior ventricular unloading in single ventricle patients and suggest impaired filling leads to performance degradation of pulsatile flow Vads in the single ventricularle circulation.
TL;DR: In this paper, the authors used particle image velocimetry to verify the theoretical properties of sinusoidally-pulsing flows of Womersley numbers 1.4 ≤ Wo ≤ 7.9.
TL;DR: Changes to aortic hemodynamics as the result of dissection were characterized including flow reversal, large exit tear vortices, and pumping action of the mobile intimal flap, which may induce future thrombosis.
Abstract: Understanding of the hemodynamics of Type B aortic dissection may improve outcomes by informing upon patient selection, device design, and deployment strategies. This project characterized changes to aortic hemodynamics as the result of dissection. We hypothesized that dissection would lead to elevated flow reversal and disrupted pulsatile flow patterns in the aorta that can be detected and quantified by non-invasive magnetic resonance imaging. Flexible, anatomic models of both normal aorta and dissected aorta, with a mobile intimal flap containing entry and exit tears, were perfused with a physiologic pulsatile waveform. Four-dimensional phase contrast magnetic resonance (4D PCMR) imaging was used to measure the hemodynamics. These images were processed to quantify pulsatile fluid velocities, flow rate, and flow reversal. Four-dimensional flow imaging in the dissected aorta revealed pockets of reverse flow and vortices primarily in the false lumen. The dissected aorta exhibited significantly greater flow reversal in the proximal-to-mid dissection as compared to normal (21.1 ± 3.8 vs. 1.98 ± 0.4%, p 0.05), validated against external flow measurement. Pulsatile aortic hemodynamics in the presence of an anatomic, elastic dissection differed significantly from those of both steady flow through a dissection and pulsatile flow through a normal aorta. New hemodynamic features including flow reversal, large exit tear vortices, and pumping action of the mobile intimal flap, were observed. False lumen flow reversal would possess a time-averaged velocity close to stagnation, which may induce future thrombosis. Focal vortices may identify the location of tears that could be covered with a stent-graft. Future correlation of hemodynamics with outcomes may indicate which patients require earlier intervention.
TL;DR: This work presents an iterative learning control (ILC) strategy for continuous flow ventricular assist devices that minimizes the left ventricular stroke work (LVSW) and introduces a comprehensive nonlinear model for rotary blood pumps that is used for simulation and controller design.
TL;DR: Results indicate that Maximal expression of relevant genes because of pulsatile treatment with hormones suggests that this protocol provides a more suitable premise for assessing hormone-induced gene expression in isolated Sc than one involving constant exposure to hormones.
Abstract: In response to various hormonal (follicle-stimulating hormone [FSH] and testosterone [T]) and biochemical inputs, testicular Sertoli cells (Sc) produce factors that regulate spermatogenesis. A number of FSH- and T-responsive Sc-specific genes, necessary for spermatogenesis, have been identified to date. However, the hormone-induced in vitro expression pattern of most of these genes is reported to be inconsistent at various time points in primary rat Sc cultures. As a matter of convenience, cultured Sc are constantly exposed to hormones for a few hours to days in the reported literature, although Sc are exposed to pulsatile FSH and T in vivo. The major aim of the present study is to evaluate the advantage, if any, of the in vitro administration of pulsatile hormone (FSH and T in combination) treatment on gene expression of cultured Sc as compared with that of constant hormone treatment. Pulsatile treatment (a 30-min hormonal exposure every 3 h) mimicking the in vivo condition reveals a more prominent effect of hormones in augmenting gene expression as compared with constant treatment. Our results indicate that the expressions of Stem cell factor (Scf, only responsive to FSH), Claudin11 (only responsive to T) and Transferrin (both FSH- and T-responsive) mRNAs are significantly higher at 12 h upon pulsatile treatment than upon constant hormonal treatment. Maximal expression of relevant genes because of pulsatile treatment with hormones suggests that this protocol provides a more suitable premise for assessing hormone-induced gene expression in isolated Sc than one involving constant exposure to hormones.
TL;DR: The design of a novel ex vivo culture system conceived for mimicking central coronary artery hemodynamics and the results of biomechanical stimulation experiments using human saphenous vein samples proved to be a suitable device to identify ex vivo mechanical cues leading to graft adaptation.
Abstract: After coronary artery bypass grafting, structural modifications of the saphenous vein wall lead to lumen narrowing in response to the altered hemodynamic conditions. Here we present the design of a novel ex vivo culture system conceived for mimicking central coronary artery hemodynamics, and we report the results of biomechanical stimulation experiments using human saphenous vein samples. The novel pulsatile system used an aortic-like pressure for forcing a time-dependent coronary-like resistance to obtain the corresponding coronary-like flow rate. The obtained pulsatile pressures and flow rates (diastolic/systolic: 80/120 mmHg and 200/100 mL/min, respectively) showed a reliable mimicking of the complex coronary hemodynamic environment. Saphenous vein segments from patients undergoing coronary artery bypass grafting (n = 12) were subjected to stimulation in our bioreactor with coronary pulsatile pressure/flow patterns or with venous-like perfusion. After 7-day stimulation, SVs were fixed and stained for morphometric evaluation and immunofluorescence. Results were compared with untreated segments of the same veins. Morphometric and immunofluorescence analysis revealed that 7 days of pulsatile stimulation: (i) did not affect integrity of the vessel wall and lumen perimeter, (ii) significantly decreased both intima and media thickness, (iii) led to partial endothelial denudation, and (iv) induced apoptosis in the vessel wall. These data are consistent with the early vessel remodeling events involved in venous bypass adaptation to arterial flow/pressure patterns. The pulsatile system proved to be a suitable device to identify ex vivo mechanical cues leading to graft adaptation.
TL;DR: Mimicking a physiological blood flow in stenotic arteries to provide an understanding of hemodynamic parameters and results can be applied in study of plaque growth and mechanisms of arterial remodeling in atherosclerosis.
Abstract: Many cardiovascular diseases are closely associated with hemodynamic parameters. The main purpose of this study is mimicking a physiological blood flow in stenotic arteries to provide an understanding of hemodynamic parameters. An experimental setup was designed to produce original pulsatile flow and measure pressure pulse waves through a compliant tube. Moreover, a numerical model considering fluid-solid interaction was developed to investigate wall shear stress and circumferential stress waves, based on the results of the experiments. Results described elevated mean pressure by increasing stenosis severity especially at the critical obstacle of 50 %, which the pressure rose significantly and raised up by 10 mm Hg that may cause damage in endothelial cells. Increasing in stenosis severity led to: more negative wall shear stress and more oscillation of shear stress at the post-stenotic region and also more absolute value of angular phase difference between wall shear stress and circumferential stress waves at the stenotic throat. All of the aforementioned parameters determinant the endothelial cell pathology in predication of potential sites of progression of atherosclerotic plaques. Therefore, results can be applied in study of plaque growth and mechanisms of arterial remodeling in atherosclerosis.
TL;DR: Results indicate that the curvature of the tube considerably influences the skewness of the flow, and the shear stress is intensified near the outer curvature wall due to centrifugal force.
Abstract: Spatial and temporal variations of the hemodynamic features occur under pulsatile conditions in complex vessel geometry. Wall shear stress affected by the disturbed flow can result in endothelial cell dysfunction, which leads to atherogenesis and thrombosis. Therefore, detailed understanding of the hemodynamic characteristics in a curved stenosed channel is highly important when examining the pathological effects of hemodynamic phenomena on the progression of atherosclerosis. The present study measures the velocity fields of pulsatile flows with three different Reynolds numbers in 3D curved vessel models with stenosis using time-resolved particle image velocimetry (PIV). Three different models were cast in PDMS polymer using models made by a 3D printer with different bend angles of 0°, 10°, and 20° between the longitudinal axes at the upstream and downstream of the stenosis. To investigate the 3D flow structures, a stack of 2D velocity fields was obtained by adjusting the position of the laser sheet along the Z-direction. The structures of flow fields in the stenosed models were analyzed using the distribution of the shearing strain as well as the skewness and full width at half maximum of the velocity profile. To support experiment results, distributions of pressure and 3D vortex in the curved stenosed channels were estimated by conducting the numerical simulation. These results indicate that the curvature of the tube considerably influences the skewness of the flow, and the shear stress is intensified near the outer curvature wall due to centrifugal force. The results would be helpful in understanding the effects of geometrical factors on plaque rupture and severe cardiovascular diseases.
TL;DR: Flow waveforms entering the brain showed similar pattern to central aortic pressure waveforms, and similar changes with age, and high pulsations in older patients are attributable to high pulsatile pressure tearing the delicate media, causing haemorrhage and microinfarcts.
Abstract: BACKGROUND Cerebral syndromes in older humans, secondary stroke in younger persons following trauma, and sickle cell anaemia in children, are linked by unexplained microvascular damage and high cerebral pressure or flow pulsations. The aim of this study was to characterize age-related pressure and flow waveforms patterns entering the brain, to explain these in terms of disturbed physiological function, and to consider clinical implications. METHOD Blood flow velocity waves were measured in four cerebral vascular territories by transcranial Doppler of 1020 apparently normal patients (497 men, 21-78 years). Central pressure waveforms were generated from radial artery applanation tonometry with SphygmoCor. Relationships were described in time and frequency domains. RESULTS AND CONCLUSION Flow waveforms entering the brain showed similar pattern to central aortic pressure waveforms, and similar changes with age. Augmentation index of flow and of pressure had high correlation at different ages, and in men and women (r = 0.58, P < 0.01). Calculated cerebral vascular impedance was similar in both sexes, and at different ages, with low modulus and phase, indicating a dilated, passive cerebral vascular bed. This vascular bed is subject to pressure and flow fluctuations generated directly by the heart and boosted by strong wave reflections from the lower body. CONCLUSION Cerebral microvascular damage in older patients is attributable to high pulsatile pressure tearing the delicate media, causing haemorrhage, and high pulsatile flow dislodging endothelial cells, causing thrombosis and microinfarcts. High pulsations in older patients are caused by early wave reflection from the lower body. Reduction of or delay in wave reflection is a logical strategy for aortic stiffening in older humans.
TL;DR: An overview of the design challenges associated with scaling the low-shear pulsatile TORVAD ventricular assist device (VAD) for treating pediatric heart failure is provided.
Abstract: This article provides an overview of the design challenges associated with scaling the low-shear pulsatile TORVAD ventricular assist device (VAD) for treating pediatric heart failure. A cardiovascular system model was used to determine that a 15 ml stroke volume device with a maximum flow rate of 4 L/min can provide full support to pediatric patients with body surface areas between 0.6 and 1.5 m. Low-shear stress in the blood is preserved as the device is scaled down and remains at least two orders of magnitude less than continuous flow VADs. A new magnetic linkage coupling the rotor and piston has been optimized using a finite element model (FEM) resulting in increased heat transfer to the blood while reducing the overall size of TORVAD. Motor FEM has also been used to reduce motor size and improve motor efficiency and heat transfer. FEM analysis predicts no more than 1°C temperature rise on any blood or tissue contacting surface of the device. The iterative computational approach established provides a methodology for developing a TORVAD platform technology with various device sizes for supporting the circulation of infants to adults.
TL;DR: The definition of pulsatility is reviewed, the outcomes of CPB using pulsatile and nonpulsatile pumps, and how best to produce and assess pulsatility are reviewed.
Abstract: Introduction: The benefits and disadvantages of pulsatility in mechanical circulatory support devices have been argued since before the first use of cardiopulmonary bypass (CPB) with a nonpulsatile pump. The debate over the superiority of either pulsatile or nonpulsatile perfusion during CPB persists, but recently, the evidence in favor of pulsatile perfusion during CPB is increasing. Complications associated with chronic nonpulsatile flow in patients implanted with left ventricular assist devices have renewed interest in generating pulsatility with these devices.Areas covered: Here we review the definition of pulsatility, the outcomes of CPB using pulsatile and nonpulsatile pumps, and how best to produce and assess pulsatility. This information was identified through online databases and direct extraction of single studies cited in previously identified reports.Expert commentary: The newer generation of biocompatible pulsatile pumps that can generate physiologic pulsation may prove beneficial dur...
TL;DR: In this article, the time-asymptotic linear stability of pulsatile flow in a channel with compliant walls is studied together with the evaluation of modal transient growth within the pulsation period of the basic flow as well as non-modal transient growing.
Abstract: The time-asymptotic linear stability of pulsatile flow in a channel with compliant walls is studied together with the evaluation of modal transient growth within the pulsation period of the basic flow as well as non-modal transient growth. Both one (vertical-displacement) and two (vertical and axial) degrees-of-freedom compliant-wall models are implemented. Two approaches are developed to study the dynamics of the coupled fluid–structure system, the first being a Floquet analysis in which disturbances are decomposed into a product of exponential growth and a sum of harmonics, while the second is a time-stepping technique for the evolution of the fundamental solution (monodromy) matrix. A parametric study of stability in the non-dimensional parameter space, principally defined by Reynolds number ( ), Womersley number ( ) and amplitude of the applied pressure modulation ( ), is then conducted for compliant walls of fixed geometric and material properties. The flow through a rigid channel is shown to be destabilized by pulsation for low , stabilized due to Stokes-layer effects at intermediate , while the critical approaches the steady Poiseuille-flow result at high , and that these effects are made more pronounced by increasing . Wall flexibility is shown to be stabilizing throughout the range but, for the relatively stiff wall used, is more effective at high . Axial displacements are shown to have negligible effect on the results based upon only vertical deformation of the compliant wall. The effect of structural damping in the compliant-wall dynamics is destabilizing, thereby suggesting that the dominant inflectional (Rayleigh) instability is of the Class A (negative-energy) type. It is shown that very high levels of modal transient growth can occur at low , and this mechanism could therefore be more important than asymptotic amplification in causing transition to turbulent flow for two-dimensional disturbances. Wall flexibility is shown to ameliorate mildly this phenomenon. As is increased, modal transient growth becomes progressively less important and the non-modal mechanism can cause similar levels of transient growth. We also show that oblique waves having non-zero transverse wavenumbers are stable to higher values of critical than their two-dimensional counterparts. Finally, we identify an additional instability branch at high that corresponds to wall-based travelling-wave flutter. We show that this is stabilized by the inclusion of structural damping, thereby confirming that it is of the Class B (positive-energy) instability type.
TL;DR: Steady or pulsatile ECMO flow, residual or no cardiac output, and intraaortic balloon pump counterpulsation were tested as independent factors and central cannulation provided the best hemodynamics and oxygen supply to the brain.
Abstract: Blood oxygenized by veno-arterial extracorporeal membrane oxygenation (ECMO) can be returned to the aorta (central cannulation) or to peripheral arteries (axillar, femoral). Hemodynamic effects of these cannulation types were analyzed in a mock loop with an aortic model representative of normal anatomy and compliance under physiological pressures and flow rates. Pressures, flow rates, and contribution of ECMO flow to total flow as a measure of oxygen supply were monitored in the carotids. Steady or pulsatile ECMO flow, residual or no cardiac output, and intraaortic balloon pump counterpulsation were tested as independent factors. With residual heart function, central cannulation provided the best oxygenated flow and pressure to the carotid arteries (CA). Axillar cannulation preferentially perfused the right CA at the expense of the left CA. Femoral cannulation provided only lower amounts of oxygenated blood to both CA. Pulsation increased the surplus hemodynamic energy. Counterpulsation reduced flow with femoral cannulation but improved flow and pressure with axillar cannulation. Femoral cannulation failed to provide oxygenated blood to coronary and supraaortic arteries with residual heart function. Central cannulation provided the best hemodynamics and oxygen supply to the brain. With a resting heart but not with an ejecting heart, pulsatile ECMO flow enhanced CA hemodynamics.
TL;DR: TEVAR was associated with an increase of pulsatile longitudinal strains (in the arch) and circumferential strains (at the celiac trunk) in unstented aortic segments, which may contribute to the understanding of stent-graft–related complications such as retrograde dissection, aneurysm formation, and rupture.
Abstract: Purpose: To quantify both pulsatile longitudinal and circumferential aortic strains before and after thoracic endovascular aortic repair (TEVAR), potentially clarifying TEVAR-related complications. Methods: This retrospective study assessed the impact of TEVAR on pulsatile aortic strains through custom developed software and cardiac-gated computed tomography imaging of 8 thoracic aneurysm patients (mean age 71.0±8.2 years; 6 men) performed before TEVAR and during follow-up (median 0.1 months, interquartile range 0.1–5.8). Lengths of the ascending aorta, the aortic arch, and the descending aorta were measured. Diameters and areas were computed at the sinotubular junction, brachiocephalic trunk, left subclavian artery, and the celiac trunk. Pulsatile longitudinal and circumferential strains were quantified as systolic increments of length and circumference divided by the corresponding diastolic values. Results: Average pulsatile longitudinal strain ranged from 1.4% to 7.1%, was highest in the arch (p<0.001)...