Showing papers on "Pulsatile flow published in 2008"
TL;DR: The overall levels of the viscous stresses are apparently too low to induce damage to red blood cells, but could potentially damage platelets, and it is shown that the so-called Reynolds shear stresses neither directly contribute to the mechanical load on blood cells nor is a proper measurement of the mechanical Load experienced by blood cells.
Abstract: Bileaflet mechanical heart valves (BMHV) are widely used to replace diseased heart valves. Implantation of BMHV, however, has been linked with major complications, which are generally considered to be caused by mechanically induced damage of blood cells resulting from the non-physiological hemodynamics environment induced by BMHV, including regions of recirculating flow and elevated Reynolds (turbulence) shear stress levels. In this article, we analyze the results of 2D high-resolution velocity measurements and full 3D numerical simulation for pulsatile flow through a BMHV mounted in a model axisymmetric aorta to investigate the mechanical environment experienced by blood elements under physiologic conditions. We show that the so-called Reynolds shear stresses neither directly contribute to the mechanical load on blood cells nor is a proper measurement of the mechanical load experienced by blood cells. We also show that the overall levels of the viscous stresses, which comprise the actual flow environment experienced by cells, are apparently too low to induce damage to red blood cells, but could potentially damage platelets. The maximum instantaneous viscous shear stress observed throughout a cardiac cycle is <15 N/m2. Our analysis is restricted to the flow downstream of the valve leaflets and thus does not address other areas within the BMHV where potentially hemodynamically hazardous levels of viscous stresses could still occur (such as in the hinge gaps and leakage jets).
176 citations
TL;DR: It is concluded that cell metabolism directly controls cAMP and that glucose-induced cAMP oscillations regulate the magnitude and kinetics of insulin exocytosis.
167 citations
TL;DR: Centrifugal, axial, and pulsatile LVADs all provide adequate circulatory support to maintain appropriate end-organ function in patients with end-stage heart failure, and the advantages of the newer continuous-flow devices can be safely applied to an increasing number of patients.
Abstract: Purpose Newer continuous-flow left ventricular assist devices (LVAD) have the advantage of smaller size and increased durability. Questions remain regarding the safety and effects of long-term nonpulsatile flow, despite some animal and human studies showing that end-organ function is well maintained with pulsatile or axial-flow devices. This study investigated whether centrifugal devices have similar effects on end-organ function. Methods All patients who underwent LVAD implantation as bridge-to-transplant (BTT) therapy from January 2004 through May 2007 were reviewed. Excluded were patients on biventricular support, destination therapy, temporary support, and patients who died within 30 days after LVAD implantation. The centrifugal device was the VentrAssist (Ventracor Ltd, Sydney, Australia); axial, the HeartMate II; and pulsatile, the HeartMate XVE (Thoratec Corp, Pleasanton, CA). Results During the study, 10 VentrAssist, 30 HeartMate II, and 18 HeartMate XVE devices were implanted. Among the 3 groups, age, gender, weight, duration of LVAD support, and cause of heart failure were comparable. No significant differences were found between groups with respect to baseline renal function, hepatic function, or hematologic function. At 1 and 3 months of follow-up, renal and hepatic function either improved or remained within normal limits in all groups. Conclusions Centrifugal, axial, and pulsatile LVADs all provide adequate circulatory support to maintain appropriate end-organ function in patients with end-stage heart failure. The advantages of the newer continuous-flow devices can be safely applied to an increasing number of patients. Long-term studies (>1 year) are needed to assess effects on end-organ function with continuous-flow devices, which may have important implications for use as destination therapy.
147 citations
TL;DR: The blood flow dynamics of a stenosed, subject-specific, carotid bifurcation were numerically simulated using the spectral element method and demonstrated the transitional or weakly turbulent state of the blood flow, which featured rapid velocity and pressure fluctuations in the post-stenotic region of the internal carotids artery (ICA) during systole and laminar flow during diastole.
147 citations
TL;DR: In this study, patient-specific computational fluid dynamics (CFD) models of blood flow were constructed from MRA data for three patients who had fusiform basilar aneurysms that were thrombus free and then proceeded to develop intralumenalThrombus.
Abstract: The deposition of intralumenal thrombus in intracranial aneurysms adds a risk of thrombo-embolism over and above that posed by mass effect and rupture. In addition to biochemical factors, hemodynamic factors that are governed by lumenal geometry and blood flow rates likely play an important role in the thrombus formation and deposition process. In this study, patient-specific computational fluid dynamics (CFD) models of blood flow were constructed from MRA data for three patients who had fusiform basilar aneurysms that were thrombus free and then proceeded to develop intralumenal thrombus. In order to determine whether features of the flow fields could suggest which regions had an elevated potential for thrombus deposition, the flow was modeled in the baseline, thrombus-free geometries. Pulsatile flow simulations were carried out using patient-specific inlet flow conditions measured with MR velocimetry. Newtonian and non-Newtonian blood behavior was considered. A strong similarity was found between the intra-aneurysmal regions with CFD-predicted slow, recirculating flows and the regions of thrombus deposition observed in vivo in the follow-up MR studies. In two cases with larger aneurysms, the agreement between the low velocity zones and clotted-off regions improved when non-Newtonian blood behavior was taken into account. A similarity was also found between the calculated low shear stress regions and the regions that were later observed to clot.
140 citations
TL;DR: A robust and elastic small-diameter artery was engineered from three types of vascular cells using the physiological pulsatile bioreactor and Tensile tests demonstrated that engineered vessels acquired equivalent ultimate strength and similar elastic characteristics as native arteries.
Abstract: Background— There is an essential demand for tissue engineered autologous small-diameter vascular graft, which can function in arterial high pressure and flow circulation. We investigated the potential to engineer a three-layered robust and elastic artery using a novel hemodynamically-equivalent pulsatile bioreactor.
Methods and Results— Endothelial cells (ECs), smooth muscle cells (SMCs), and fibroblasts were harvested from bovine aorta. A polyglycolic acid (PGA) sheet and a polycaprolactone sheet seeded with SMCs, and a PGA sheet seeded with fibroblast, were wrapped in turn on a 6-mm diameter silicone tube and incubated in culture medium for 30 days. The supporting tube was removed, and the lumen was seeded with ECs and incubated for another 2 days. The pulsatile bioreactor culture, under regulated gradual increase in flow and pressure from 0.2 (0.5/0) L/min and 20 (40/15) mm Hg to 0.6 (1.4/0.2) L/min and 100 (120/80) mm Hg, was performed for an additional 2 weeks (n=10). The engineered vessels acquired distinctly similar appearance and elasticity as native arteries. Scanning electron microscopic examination and Von Willebrand factor staining demonstrated the presence of ECs spread over the lumen. Elastica Van Gieson and Masson Tricrome Stain revealed ample production of elastin and collagen in the engineered grafts. Alpha-SMA and calponin staining showed the presence of SMCs. Tensile tests demonstrated that engineered vessels acquired equivalent ultimate strength and similar elastic characteristics as native arteries (Ultimate Strength of Native: 882±133 kPa, Engineered: 827±155 kPa, each n=8).
Conclusions— A robust and elastic small-diameter artery was engineered from three types of vascular cells using the physiological pulsatile bioreactor.
137 citations
TL;DR: A novel perfusion bioreactor capable of providing pulsatile fluid flow at physiologically relevant shear stresses and flow rates was constructed and the enhanced hypertrophy index observed for the PP‐LF group was consistent with the highest cellular length and diameter in this group.
Abstract: Cardiovascular disease is the number one cause of mortality in North America. Cardiac tissue engineering aims to engineer a contractile patch of physiological thickness to use in surgical repair of diseased heart tissue. We previously reported that perfusion of engineered cardiac constructs resulted in improved tissue assembly. Because heart tissues respond to mechanical stimuli in vitro and experience rhythmic mechanical forces during contraction in vivo, we hypothesized that provision of pulsatile interstitial medium flow to an engineered cardiac patch would result in enhanced tissue assembly by way of mechanical conditioning and improved mass transport. Thus, we constructed a novel perfusion bioreactor capable of providing pulsatile fluid flow at physiologically relevant shear stresses and flow rates. Pulsatile perfusion (PP) was achieved by incorporation of a normally closed solenoid pinch valve into the perfusion loop and was carried out at a frequency of 1 Hz and a flow rate of 1.50 mL/min (PP) or 0.32 mL/min (PP-LF). Nonpulsatile flow at 1.50 mL/min (NP) or 0.32 mL/min (NP-LF) served as controls. Static controls were cultivated in well plates. The main experimental groups were seeded with cells enriched for cardiomyocytes by one preplating step (64% cardiac Troponin I+, 34% prolyl-4-hydroxylase+), whereas pure cardiac fibroblasts and cells enriched for cardiomyocytes by two preplating steps (81% cardiac Troponin I+, 16% prolyl-4-hydroxylase+) served as controls. Cultivation under pulsatile flow had beneficial effects on contractile properties. Specifically, the excitation threshold was significantly lower in the PP condition (pulsatile perfusion at 1.50 mL/min) than in the Static control, and the contraction amplitude was the highest; whereas high maximum capture rate was observed for the PP-LF conditions (pulsatile perfusion at 0.32 mL/min). The enhanced hypertrophy index observed for the PP-LF group was consistent with the highest cellular length and diameter in this group. Within the same cultivation groups (Static, NP-LF, PP-LF, PP, and NP) there were no significant differences in the diameter between fibroblasts and cardiomyocytes, although cardiomyocytes were significantly more elongated than fibroblasts under PP-LF conditions. Cultivation of control cell populations resulted in noncontractile constructs when cardiac fibroblasts were used (as expected) and no overall improvement in functional properties when two steps of preplating were used to enrich for cardiomyocytes in comparison with only one step of preplating.
111 citations
TL;DR: Numerical results obtained for the positive taper angle show that the blood flow characteristics such as the axial velocity profiles, flow rate and wall shear stress have lower values, while the resistive impedances have higher values than the Newtonian model.
109 citations
TL;DR: The present study indicates increased ocular rigidity in patients with POAG, compatible with a number of previous animal experiments and supports the concepts that the biomechanical properties of ocular tissues play a role in the diseases process.
Abstract: PURPOSE. There is evidence from theoretical models and animal studies that the biomechanical properties of the optic nerve head and the sclera play a role in the pathophysiology of glaucoma. There are, however, only a few data available that demonstrate such biomechanical alterations in vivo. In this study, the hypothesis was that patients with primary openangle glaucoma (POAG) have an abnormal ocular structural stiffness based on measurements of intraocular pressure amplitude and ocular fundus pulsation amplitude (FPA). METHODS. Seventy patients with POAG and 70 healthy control subjects matched for age, sex, intraocular pressure and systemic blood pressure were included. The ocular PA and pulsatile ocular blood flow were assessed with pneumotonometry. The FPA was measured by using laser interferometry. Based on the Friedenwald equation, a coefficient of ocular rigidity (E1) was calculated relating PA to FPA. RESULTS. There was no difference in systemic blood pressure, intraocular pressure, and ocular perfusion pressure (OPP) between the patients with glaucoma and the healthy control subjects. Both, FPA and PA were lower in the patients with glaucoma than in the control subjects. The calculated factor E1 was significantly higher in the patients with POAG (0.0454 0.0085 AU) than in the control subjects (0.0427 0.0058 AU, P 0.03). Multiple regression analysis revealed that E1 was independent of age and sex, and correlated only slightly with OPP. CONCLUSIONS. The present study indicates increased ocular rigidity in patients with POAG. This is compatible with a number of previous animal experiments and supports the concepts that the biomechanical properties of ocular tissues play a role in the diseases process. (Invest Ophthalmol Vis Sci. 2008;49: 4046‐4050) DOI:10.1167/iovs.07-1342
108 citations
TL;DR: This study demonstrates that CFD models constructed from patient-specific magnetic resonance (MR) angiography and velocimetry data predict flow fields that are in good agreement with in vivo measurements and therefore can provide valuable information for clinicians and suggests that realistic patient- specific flow conditions are required for numerical simulations of the flow in aneurysmal blood vessels.
Abstract: Computational fluid dynamics (CFD) methods can be used to compute the velocity field in patient-specific vascular geometries for pulsatile physiological flow. Those simulations require geometric and hemodynamic boundary values. The purpose of this study is to demonstrate that CFD models constructed from patient-specific magnetic resonance (MR) angiography and velocimetry data predict flow fields that are in good agreement with in vivo measurements and therefore can provide valuable information for clinicians. The effect of the inlet flow rate conditions on calculated velocity fields was investigated. We assessed the internal consistency of our approach by comparing CFD predictions of the in-plane velocity field to the corresponding in vivo MR velocimetry measurements. Patient-specific surface models of four basilar artery aneurysms were constructed from contrast-enhanced MR angiography data. CFD simulations were carried out in those models using patient-specific flow conditions extracted from MR velocity measurements of flow in the inlet vessels. The simulation results computed for slices through the vasculature of interest were compared with in-plane velocity measurements acquired with phase-contrast MR imaging in vivo. The sensitivity of the flow fields to inlet flow ratio variations was assessed by simulating five different inlet flow scenarios for each of the basilar aneurysm models. In the majority of cases, altering the inlet flow ratio caused major changes in the flow fields predicted in the aneurysm. A good agreement was found between the flow fields measured in vivo using the in-plane MR velocimetry technique and those predicted with CFD simulations. The study serves to demonstrate the consistency and reliability of both MR imaging and numerical modeling methods. The results demonstrate the clinical relevance of computational models and suggest that realistic patient-specific flow conditions are required for numerical simulations of the flow in aneurysmal blood vessels.
103 citations
TL;DR: In general, the three-layer stents seem not as effective as the two- layer stents in reducing the magnitude of aneurysm inflow rate and WSS.
TL;DR: Blood flow in end-to-side autogenous or prosthetic graft anastomoses is of great interest to biomedical researchers because the biomechanical force profile engendered by blood flow disturbances at such geometric transitions is thought to play a significant role in vascular remodeling and graft failure.
Abstract: Blood flow in end-to-side autogenous or prosthetic graft anastomoses is of great interest to biomedical researchers because the biomechanical force profile engendered by blood flow disturbances at such geometric transitions is thought to play a significant role in vascular remodeling and graft failure. Thus, investigators have extensively studied anastomotic blood flow patterns in relation to graft failure with the objective of enabling the design of a more optimal graft anastomotic geometry. In contrast to arterial bifurcations, surgically created anastomoses can be modified to yield a flow environment that improves graft longevity. Understanding blood flow patterns at anastomotic junctions is a challenging problem because of the highly varying and complex three-dimensional nature of the geometry that is subjected to pulsatile and, occasionally, turbulent flow.
TL;DR: In this article, the authors show that suitable initial disturbances to steady or long-period pulsatile flows in a straight tube with an axisymmetric 75-occlusion stenosis can produce very large transient energy growths.
Abstract: We show that suitable initial disturbances to steady or long-period pulsatile flows in a straight tube with an axisymmetric 75%-occlusion stenosis can produce very large transient energy growths. The global optimal disturbances to an initially axisymmetric state found by linear analyses are three-dimensional wave packets that produce localized sinuous convective instability in extended shear layers. In pulsatile flow, initial conditions that trigger the largest disturbances are either initiated at, or advect to, the separating shear layer at the stenosis in phase with peak systolic flow. Movies are available with the online version of the paper.
TL;DR: The reduced pulsatility produced by a continuous flow LVAD implantation induced severe periarteritis in the kidneys, and the local renin-angiotensin system was up-regulated in the inflammatory cells only in the continuous flowLVAD group.
TL;DR: In this study, newly developed two-equation turbulence models and transitional variants are employed for the prediction of blood flow patterns in a diseased carotid artery where the growth, progression, and structure of the plaque at rupture are closely linked to low and oscillating wall shear stresses.
Abstract: In this study, newly developed two-equation turbulence models and transitional variants are employed for the prediction of blood flow patterns in a diseased carotid artery where the growth, progression, and structure of the plaque at rupture are closely linked to low and oscillating wall shear stresses. Moreover, the laminar-turbulent transition in the poststenotic zone can alter the separation zone length, wall shear stress, and pressure distribution over the plaque, with potential implications for stresses within the plaque. Following the validation with well established experimental measurements and numerical studies, a magnetic-resonance (MR) image-based model of the carotid bifurcation with 70% stenosis was reconstructed and simulated using realistic patient-specific conditions. Laminar flow, a correlation-based transitional version of Menter's hybrid k-epsilon/k-omega shear stress transport (SST) model and its "scale adaptive simulation" (SAS) variant were implemented in pulsatile simulations from which analyses of velocity profiles, wall shear stress, and turbulence intensity were conducted. In general, the transitional version of SST and its SAS variant are shown to give a better overall agreement than their standard counterparts with experimental data for pulsatile flow in an axisymmetric stenosed tube. For the patient-specific case reported, the wall shear stress analysis showed discernable differences between the laminar flow and SST transitional models but virtually no difference between the SST transitional model and its SAS variant.
TL;DR: Various systems like capsular systems, osmotic systems, pulsatile system based on the use of soluble or erodible polymer coating, use of rupturable membranes and pulsatileSystem based on membrane permeability are summarized in this article.
Abstract: Pulsatile drug delivery system is the most interesting time- and site-specific system. This system is designed for chronopharmacotherapy which is based on circadian rhythm. The principle rationale for the use of pulsatile release is for the drugs where a constant drug release, i.e., a zero-order release is not desired. Pulsatile drug delivery system is defined as the rapid and transient release of certain amount of molecules within a short time period immediately after a predetermined off-release period, i.e., lag time. Various systems like capsular systems, osmotic systems, pulsatile system based on the use of soluble or erodible polymer coating, use of rupturable membranes and pulsatile system based on membrane permeability are summarized in this article.These systems are beneficial for the drugs having chronopharmacological behavior where night time dosing is required and for the drugs having high first-pass effect and having specific site of absorption in gastrointestinal tract.
TL;DR: Substantial left ventricular unloading and hemodynamic improvement is achieved with the HeartMate XVE and theHeartMate II, and it is concluded that continuous-flow LVADs are as effective as pulsatile-flowLVADs with regard to degree ofleft ventricularunloading and cardiac hemodynamics.
Abstract: Background In patients with end-stage heart failure, the use of left ventricular assist devices (LVADs) has improved clinical outcomes. Although newer continuous-flow devices have significant advantages, the effect of continuous flow on left ventricular unloading and hemodynamics is less well established. The aim of this investigation was to compare the effects of pulsatile- vs continuous-flow LVADs on left ventricular reverse remodeling and hemodynamic indices. Methods Thirty-five patients undergoing implantation with a pulsatile volume displacement pump operating at fixed speed ( n = 15; HeartMate XVE; Thoratec Corp., Pleasanton, CA) or a continuous-flow rotary pump with an axial design operating at a fixed rotor speed ( n = 20; HeartMate II; Thoratec) were evaluated. Right heart catheterization and echocardiography were performed pre-operatively, and at 1- and 6-month follow-up intervals. Results Thirty-five of 40 eligible patients with end-stage heart failure were included in this study. When used at fixed speed, use of both devices led to a substantial reduction in left ventricular volumes and dimensions at 1 month ( p p p -values not statistically significant). Conclusions Substantial left ventricular unloading and hemodynamic improvement is achieved with the HeartMate XVE and the HeartMate II. We conclude that continuous-flow LVADs are as effective as pulsatile-flow LVADs with regard to degree of left ventricular unloading and cardiac hemodynamics.
TL;DR: After LVAD implantation, patients with continuous flow devices and patients with pulsatile flow devices have comparable renal function and no significant increase occurred in mean GFR/CrCl to transplantation.
Abstract: Background This study was designed to determine the effect of continuous vs pulsatile flow devices on renal function after left ventricular assist device (LVAD) implantation. Methods Ninety-two patients undergoing LVAD implantation as bridge-to-transplant therapy were retrospectively analyzed. Patients receiving continuous flow devices (n = 63, 68.5%) were compared with patients receiving pulsatile flow devices (n = 29, 31.5%). Renal function was assessed by 2 calculated glomerular filtration rates (GFR) using the Modification of Diet in Renal Disease (MDRD)-derived GFR (ml/min/1.73 m 2 ) and the Cockcroft-Gault–derived creatinine clearance (CrCl, ml/min). Results Mean GFR/CrCl was comparable between the groups at LVAD implantation, in the post-implantation period, and at transplantation. Both groups had a significant increase in mean GFR at Week 1 post-implantation (continuous, 59.4 ± 22.8 to 76.4 ± 38.6, p = 0.001; pulsatile, 52.5 ± 21.1 to 69.2 ± 34.7; p = 0.007), Week 4 (continuous, 59.9 ± 23.0 to 84.3 ± 32.9; p p = 0.007), and Week 12 (continuous, 60.3 ± 23.1 to 75.3 ± 30.2, p = 0.004; pulsatile, 55.5 ± 23.1 to 74.2 ± 27.2, p = 0.037) that was also seen with the Cockcroft-Gault–calculated CrCl. No significant increase occurred in mean GFR/CrCl to transplantation. Incidence of post-implantation renal failure was comparable between the groups (continuous, 38.1%; pulsatile, 31.0%; p = 0.512). Conclusions After LVAD implantation, patients with continuous flow devices and patients with pulsatile flow devices have comparable renal function.
TL;DR: Three-phase computational fluid dynamics approach including plasma, RBCs, and leukocytes was used to numerically simulate the local hemodynamics in such a flow regime and the predicted higher leukocyte concentration was correlated with relatively low WSS near the stenosis having a high WSS.
TL;DR: The engineered vessels under dynamic culture exhibited significant improvements on biomechanical property over the one from static culture, indicating that the approach developed in the current work is efficient for large vessel engineering.
TL;DR: The unsteady pulsatile flow of blood in an artery is studied, where the effects of body acceleration are included and the blood is modeled as a modified second-grade fluid where the viscosity and the normal stress coefficients depend on the shear rate.
Abstract: We study the unsteady pulsatile flow of blood in an artery, where the effects of body acceleration are included. The blood is modeled as a modified second-grade fluid where the viscosity and the normal stress coefficients depend on the shear rate. It is assumed that the blood near the wall behaves as a Newtonian fluid, and in the core as a non-Newtonian fluid. This phenomenon is also known as the Fahraeus-Lindqvist effect. The equations are made dimensionless and solved numerically.
TL;DR: It is hypothesized that avoiding ischemia of the lungs during CPB by active pulmonary perfusion would decrease pulmonary inflammatory response and apoptosis in the lungs observed during conventional CPB.
TL;DR: An analytically-based computational model based on the Womersley equations for pulsatile blood flow within elastic and viscoelastic arteries concludes that longitudinal wall displacements comparable to the radial displacements can be present and should be considered when studying the effects of tissue movement on Doppler ultrasound clutter.
Abstract: The existing computational model studies of pulsatile blood flow in arteries have assumed either rigid wall characteristics or elastic arterial wall behavior with wall movement limited to the radial direction. Recent in vivo studies have identified significant viscoelastic wall properties and longitudinal wall displacements over the cardiac cycle. Determining the nature of these movements is important for predicting the effects of ultrasound clutter in Doppler ultrasound measurements. It is also important for developing an improved understanding of the physiology of vessel wall motion. We present an analytically-based computational model based on the Womersley equations for pulsatile blood flow within elastic and viscoelastic arteries. By comparison with published in vivo data of the human common carotid artery as well as uncertainty and sensitivity analyses, it is found that the predicted waveforms are in reasonable quantitative agreement. Either a pressure, pressure gradient or volumetric flow rate waveform over a single cardiac cycle is used as an input. Outputs include the pressure, pressure gradient, radial and longitudinal fluid velocities and arterial wall displacements, volumetric flow rate and average longitudinal velocity. It is concluded that longitudinal wall displacements comparable to the radial displacements can be present and should be considered when studying the effects of tissue movement on Doppler ultrasound clutter.
TL;DR: Assessment of arterial stiffness and vascular load in systolic heart failure and in heart failure with a normal ejection fraction is described, and the importance of optimal ventricular-vascular coupling to maximize the efficiency of cardiac ejection is discussed.
Abstract: Vascular load is an important determinant of ventricular function This is particularly true of the failing heart, which is exquisitely load-sensitive Vascular load comprises 2 major components: resistive load, which arises primarily at the arteriolar resistance vessels, and pulsatile load, which is primarily determined by aortic stiffness and early return of reflected waves from the periphery to the heart Assessment of pulsatile load is gaining increasing prominence as evidence grows of a significant pathophysiologic role for arterial stiffness in cardiovascular disease, including heart failure Assessment of arterial stiffness and vascular load is reviewed here The importance of optimal ventricular-vascular coupling to maximize the efficiency of cardiac ejection is discussed Current knowledge of arterial stiffness, vascular load, and ventricular-vascular coupling in systolic heart failure and in heart failure with a normal ejection fraction ("diastolic failure") is described Reducing aortic stiffness may form an important future therapeutic target in patients with heart failure
TL;DR: The present chapter details new aspects of the cyclic blood pressure curve that should be characterized from pulsatile arterial hemodynamics, leading to the definition of novel indices in CV epidemiology.
Abstract: For many years, the cyclic blood pressure (BP) curve was described exclusively from two specific points of this curve, the highest, called systolic blood pressure, and the lowest, called diastolic blood pressure, both dominating the basis of cardiovascular (CV) hypertensive epidemiology. Nowadays, it is largely admitted that the BP curve should be characterized from pulsatile arterial hemodynamics, thus leading to the definition of novel indices in CV epidemiology. The present chapter details these new aspects.
TL;DR: Results show that conductivity correlates with the spatial average blood velocity and that features of the velocity waveform are reproduced in the conductivity signal, supporting the reliability of the model.
Abstract: The electrical impedance of blood is used in biomedical applications such as impedance cardiography for monitoring blood flow. Impedance cardiography assumes a constant value for the conductivity of blood. However, this assumption has been shown to be invalid for the case of flowing blood since the conductivity is affected by flow induced changes in the orientation of red blood cells. A number of previous studies have modeled the conductivity of blood in constant flow. This study investigates the conductivity changes due to pulsatile flow as experienced during the cardiac cycle. This is achieved through the development of a theoretical model of the conductivity of pulsatile blood flowing through rigid tubes. Conductivity waveforms of pulsatile blood were generated by incorporating realistic physiological flow and cell orientation dynamics into previously reported steady flow conductivity models. Results show that conductivity correlates with the spatial average blood velocity and that features of the velocity waveform are reproduced in the conductivity signal. Conductivity was also shown to be dependent on the shape of the velocity profile. The modeled conductivity change is comparable with previously published experimental results for pulsatile blood flow, supporting the reliability of the model.
TL;DR: The traditional approach of total artificial heart (TAH) and ventricular assist device (VAD) development has been the mimicking of the native heart while the combination of bioengineering superiority and the maintenance of physiologic homeostasis has directed future TAH and VAD research towards nonpulsatile systems.
Abstract: The traditional approach of total artificial heart (TAH) and ventricular assist device (VAD) development has been the mimicking of the native heart. Nonpulsatile flow using cardiopulmonary bypass has provided evidence of short-term physiologic tolerances. The design of nonpulsatile TAHs and VADs has eliminated the need for valves, flexing diaphragms, and large ventricular volumes. However, these devices require high efficiency power sources and reliable bearing seals or electromagnetic bearings while simultaneously attempting to avoid thromboemboli. The physiologic response to nonpulsatile flow is complex and variable. When compared to a pulsatile device, a nonpulsatile TAH or VAD needs to produce increased flow and higher mean intravascular pressures to maintain normal organ function. Despite its maintaining normal organ function, nonpulsatile flow does cause alterations in biochemical functions and organ specific blood flow. The combination of bioengineering superiority and the maintenance of physiologic homeostasis has directed future TAH and VAD research towards nonpulsatile systems.
TL;DR: The detailed three-dimensional pulsatile hemodynamics, mechanical loading, and perfusion characteristics of a patient-specific neonatal aortic arch during cardiopulmonary bypass (CPB) will aid the surgical decision making process of the perfusion strategies in complex congenital heart surgeries.
Abstract: The objective of this study is to quantify the detailed three-dimensional (3D) pulsatile hemodynamics, mechanical loading, and perfusion characteristics of a patient-specific neonatal aortic arch during cardiopulmonary bypass (CPB). The 3D cardiac magnetic resonance imaging (MRI) reconstruction of a pediatric patient with a normal aortic arch is modified based on clinical literature to represent the neonatal morphology and flow conditions. The anatomical dimensions are verified from several literature sources. The CPB is created virtually in the computer by clamping the ascending aorta and inserting the computer-aided design model of the 10 Fr tapered generic cannula. Pulsatile (130 bpm) 3D blood flow velocities and pressures are computed using the commercial computational fluid dynamics (CFD) software. Second order accurate CFD settings are validated against particle image velocimetry experiments in an earlier study with a complex cardiovascular unsteady benchmark. CFD results in this manuscript are further compared with the in vivo physiological CPB pressure waveforms and demonstrated excellent agreement. Cannula inlet flow waveforms are measured from in vivo PC-MRI and 3 kg piglet neonatal animal model physiological experiments, distributed equally between the head-neck vessels and the descending aorta. Neonatal 3D aortic hemodynamics is also compared with that of the pediatric and fetal aortic stages. Detailed 3D flow fields, blood damage, wall shear stress (WSS), pressure drop, perfusion, and hemodynamic parameters describing the pulsatile energetics are calculated for both the physiological neonatal aorta and for the CPB aorta assembly. The primary flow structure is the high-speed canulla jet flow (approximately 3.0 m/s at peak flow), which eventually stagnates at the anterior aortic arch wall and low velocity flow in the cross-clamp pouch. These structures contributed to the reduced flow pulsatility (85%), increased WSS (50%), power loss (28%), and blood damage (288%), compared with normal neonatal aortic physiology. These drastic hemodynamic differences and associated intense biophysical loading of the pathological CPB configuration necessitate urgent bioengineering improvements--in hardware design, perfusion flow waveform, and configuration. This study serves to document the baseline condition, while the methodology presented can be utilized in preliminary CPB cannula design and in optimization studies reducing animal experiments. Coupled to a lumped-parameter model the 3D hemodynamic characteristics will aid the surgical decision making process of the perfusion strategies in complex congenital heart surgeries.
TL;DR: In the experience, when compared to pulsatile LVAD, continuous-flow pumps are similarly effective in transplant rate and post-transplant outcome.
Abstract: Background: Long-term implantable continuous axial-flow pumps are increasingly used in bridging heart failure patients to heart transplant. Compared to pulsatile left ventricular assist devices (LVADs), they offer smaller dimensions, less surgical trauma and less thromboembolisms. However concerns still remain about the long-term effects of continuous-flow on patients’ outcome. The aim of this study was to review our mechanical bridge to transplant experience to compare pre- and post-transplant outcomes between pulsatile and continuous-flow LVAD recipients. Methods: Thirty-six patients with a continuous-flow device (Micromed DeBakey, Houston, TX or InCor Berlin Heart, Berlin, Germany — group A) were compared with 41 patients supported with a pulsatile device (Novacor W , WorldHeart, Oakland, CA — group B). Results: Mean age (48.6 12.4 vs 47.2 12.5) and LVAD duration (119.3 115.4 vs 128.3 198.3) were similar in the two groups. Group A recipients were smaller compared to group B (mean body surface area = 1.77 0.18 vs 1.93 0.16; p < 0.001). Idiopathic dilated cardiomyopathy was not significantly greater between the two groups (78% vs 58.3%; p = 0.085). Successful bridging to transplantation was similar in group A compared to group B (52.8% vs 63.4%; p = non significant). On-VAD mortality was similar between the two groups (A vs B = 33.3% vs 36.6%; p = non significant). Thirtyday mortality after HTx in group A was 10.5% compared to 7.7% in group B (p = non significant). First year post-transplant incidence of treated rejections(36.8%vs46%;p = nonsignificant)asthemeannumberofrejection/patient(0.38 0.5vs0.53 0.83;p = nonsignificant)weresimilar in group A compared to group B. Conclusions: In our experience, when compared to pulsatile LVAD, continuous-flow pumps are similarly effective in transplant rate and post-transplant outcome. # 2008 European Association for Cardio-Thoracic Surgery. Published by Elsevier B.V. All rights reserved.
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01 Mar 2008TL;DR: The data reported are consistent with the hypothesis that low wall shear stress is associated with the localization of atherosclerotic lesions, and the results demonstrate the importance of aortic flow on flow patterns in the proximal segments of the coronary arteries.
Abstract: Atherosclerotic plaques in human coronary arteries are focal manifestations of systemic disease, and biomechanical factors have been hypothesized to contribute to plaque genesis and localization. We developed a computational fluid dynamics (CFD) model of the ascending aorta and proximal sections of the right and left coronary arteries of a normal human subject using computed tomography (CT) and magnetic resonance imaging (MRI) and determined the pulsatile flow field. Results demonstrate that flow patterns in the ascending aorta contribute to a pro-atherosclerotic flow environment, specifically through localization of low and oscillatory wall shear stress in the neighborhood of coronary orifices. Furthermore, these patterns differ in their spatial distribution between right and left coronary arteries. Entrance effects of aortic flow diminish within two vessel diameters. We examined relationships between spatial distributions of wall shear stress and reports of plaque occurrence in the literature. Results indicate low wall shear stress is co-located with increased incidence of lesions, and higher wall shear stresses are associated with lesion-resistant areas. This investigation does not consider plaque progression or advanced lesions, inasmuch as the CFD model was developed from a normal individual and the clinical data used for comparisons were obtained from autopsy specimens of subjects who died from non-cardiovascular causes. The data reported are consistent with the hypothesis that low wall shear stress is associated with the localization of atherosclerotic lesions, and the results demonstrate the importance of aortic flow on flow patterns in the proximal segments of the coronary arteries.