Biomechanical Manifestations of Diastolic and Systolic Function in Rats with Heart Failure with Preserved Ejection Fraction

Objective Heart failure(HF)is divided into two types:Heart failure with reduced ejection fraction(HFrEF)and heart failure with preserved ejection fraction(HFpEF).The latter always results in diastolic dysfunction,characterized by changes in mechanical properties.The objective of this study is to build a finite element(FE)model of HFpEF and analyze diastolic and systolic function in rats.Methods Ten Dahl salt-sensitive rats were fed either a low-salt(LS)(n=5)or highsalt(HS)(n=5)diet beginning at 7 weeks of age and scanned by ultrasonic machine at 14 weeks of age.A non-linear FE model of the left ventricle(LV)was built from cardiac echo images at end-diastole and passive material properties of the LV were prescribed using Fung’s transversely isotropic constitutive law.Fiber angles of the endocardium and epicardium were prescribed as 53°°and-52°,respectively,with respect to the circumferential direction and varied linearly through the LV wall.The method developed by Krishnamurthywas used to determine the unloaded geometry to estimate the Fung passive material parameters.LV end-diastolic pressure(EDP)was determined from the measured pressure waves and applied to the endocardium at the unloaded geometry to simulate passive filling.Active material properties of the LV were prescribed using Guccione’s time-varying elastance model and maximum isometric tension was scaled to match the measured peak systolic pressure.The finite element model was then coupled to the Windkessel model,whose parameters were adjusted to the measured hemodynamics.Results Measured LVEDPs of LS and HS rats were 4.9±3.4 mmHg and 13.2±5.4 mmHg(P-0.030 8),respectively.End-diastolic Cauchy stress along the fiber direction for LS rats was significantly lower than for HS rats(0.91±0.60 kPa vs 3.00±0.63 kPa,P=0.001 4)and there was a similar trend in end-diastolic Green Strain along the fiber direction(0.058±0.003 vs 0.072±0.010,P=0.012 8,Figure 1b),as well.There was no distinctive difference between end-systolic Cauchy stress along the fiber direction for LS rats and HS rats(17.2±4.3 kPa vs 17.2±5.5 kPa,P=0.991 9)but end-systolic Green Strain along the fiber direction for LS rats was significantly higher than for HS rats(-0. 108±0.017 vs-0.065±0.024,negative sign represents direction).Conclusions For rats with HFpEF,it is the elevated LVEDP that induces the increase in end-diastolic stress and strain,thereby leading to diastolic dysfunction.Because of the preserved ejection fraction,HFpEF has less effect on systolic function.

Fluid-Structure Interaction Modeling of the Living Artery: Based on the Zero-Pressure Status and the Anisotropic Hyperelastic Constitutive Model

Vascular diseases such as aneurysm,hemadostenosis,aortic dissection are the primary causes of people’s death around world.As a result,it is significant to improve our knowledge about them,which can help to treat the disease.Measuring the hemodynamic factor like the blood pressure,the wall shear stress(WSS)and the oscillatory shear index(OSI)is,however,still beyond the capabilities of in-vivo measurement techniques.So the use of mathematical models and numerical simulations for the studies of the blood flow in arteries and,in general,of the cardiovascular system,both in physiological and pathological conditions,has received an increasing attention in the biomedical community during the last two decades.Indeed,such studies aims at enhancing the current knowledge of the physiology of the cardiovascular system,as well as providing reliable tools for the medical doctors to predict the natural course of pathologies and,possibly,the occurrence of cardiovascular accidents.The computational vascular fluid-structure interaction(FSI)methodology is a numerical simulation method which is used to explain the hemodynamic factors.The WSS on the luminal wall and the mechanical stress in the vascular wall are directly related to the location of the lesion,and the blood flow strongly interacts with the vascular wall motion.The arterial wall continually adapts to the charge of its mechanical environment(due to,for example,growth,atrophy,remodelling,repair,ageing,and disease)and consequently undergoes several irreversible processes.Primary acute mechanisms of vascularFSI numerical simulation seem to be associated with(1)the arterial histology and the patient-specific complex geometry,(2)the typical mechanical properties of the layer,(3)properties of the blood is assumed as Newtonian fluid or non-Newtonian fluid based on the scale ofthe diameter of a vessel,(4)residual stress in the zero-pressure configuration.The arterial system naturally function under permanent physiological loading conditions.Fung defined the residual stress and measured the opening angle which varies greatly along the aortic tree.Consequently,most of these systems never experience a stress-free state in their’service life’,so a stress and strain fields are present in any in vivo obtained patientspecific cardiovascular geometry.The residual stress always be ignored in FSI simulation or be assumed to equal zero,and the vivo patient-specific artery geometry is assumed as zero-pressure configuration.To define the in vivo stress state of artery,an inverse problem needs to be solved:the undeformed shape of a body or its stress state in its deformed state needs to be determined given the deformed configuration and the loads causing this deformation.The modular inverse elastostatics method is used to resolve the pressure-induced stress state for in vivo imaging based on cardiovascular modeling proposed by Peirlinck.Here,we build a living vessel FSI model based on 4 key factors.In order to get the universal simulation results,we focus on idealized geometries of the vessel that represent healthy(physiological)conditions of the cerebral vasculature.Blood can be assumed as the Newtonian fluid at this scale.The anisotropic hyperelastic constitutive law(Gasser-Holzapfel-Ogden)is used in zero-pressure configuration.Afterwards,we propose the material parameters for the different constitutive models and the computational configurations.We demonstrate the importance of introducing the residual stress into vascular blood flow modeling by performing a comparing zero-pressure configuration and no-resistance configuration.We get the conclusion that the zero-pressure status model has smaller displacement and larger stress distribution compared with no-resistance stress model.Hence,the methodology presented here will be particularly useful to study the mechanobiological processes in the healthy and diseased vascular wall.

A Texture-Based Multi Scale Analysis on Rat’s Arteries Relating to Location and Aging

The bridge between macro and micro scale has been arousing people’s attention for years.As for the vessel wall,the link between material property and microstructural network remains unknown,leaving potential possibility to discover the intrinsic mechanism of biological compound material.The objective of the study is to perform a novel analysis method to investigate how microstructure unit contributes to its mechanical characteristics and what kind of factors relating to macro properties of vessel wall may affect its micro characteristics.In this study,we chose to employ a texture analysis to describe and measure spatial network-like structure and collagen fiber alignment patterns in abdominal aorta,femoral artery and carotid artery of rats,respectively.Several first order texture statistics and second order texture statistics have been selected to be embedded into a feature matrix to characterize significance structural distinction(P<0.01)of the aforementioned types of arteries.Also,aging would also be considered as a chronic factor to affect microstructural network.The featuring matrix was then used for training a SVM classifier to predict the artery’s types,age and mechanical properties based on mechanical tests data.(Accuracy=0.86)This analysis methodreveals the link between micro and macro scale of arterial mechanics and more findings will be uncovered based on the framework in the future.

A novel stochastic reaction-diffusion model of Ca^2＋ blink in cardiac myocytes

In cardiac myocytes,the sarcoplasmic reticulum(SR)is the main storage organelle of free Ca^(2+).The concentration of free Ca^(2+)in the SR is 0.5–1.0 mmol/L and is 2–3 orders of magnitude greater than that in the cytosol.The SR is composed of interconnected cisternae(junctional SR,i.e.,JSR)and tubules(free SR network,i.e.,FSR)that extend throughout the cytosol[1].Ca^(2+)is released from the JSR into the cytosol via Ca^(2+)release units(CRUs,

基于Nb6八面体结构单元的立体芳香性性质的过渡金属一氧化物

通过对NbO氧化物的研究,本文发现NbO的周期性晶体结构中存在Nb6立体芳香性结构基元.每个Nb原子周围有4个O原子在平面配位,形成相对罕见的平面四配位结构基元.氧的空缺打破了通常的NbO6八面体对称性,因而其轨道能级也发生分裂重排.原本八面体高对称性下简并的eg和t2g轨道发生了分裂,eg中分裂出的dz2能级与t2g中分裂出dxz,dyz能量靠近和交错,增加了不同Nb原子间d轨道能级在能量上的匹配.在Nb3O3晶体中,由于Nb原子间的d轨道的能量和空间对称性的互相匹配,d轨道可以互相叠加成强烈的金属键,这些金属键有助于形成芳香性的Nb6八面体原子簇.这些八面体再共用顶点的Nb连接成三维骨架,而使得NbO具有金属Nb那样的金属光泽和导电性.

Intra-and inter-specific scaling laws of plants and animals

The allometric scaling laws of metabolism in 447 animal and 1200 plant species showed convex and concave curvatures between mass and metabolic rate,respectively.The objective of the study is to explain the difference of curvatures between animals and plants based on fractal models.Several intraspecific scaling laws were derived from an asymmetric vascular tree with the fractal dimension(i.e.,a in k^(a)_(1)+k^(a)_(2)+…-=1,where k_(i)refers to the ratio of daughter to mother diameters).Based on the intraspecific scaling laws,the allometric scaling exponent of metabolism(i.e.,an interspecific scaling law)was shown to be equal to one-third of fractal dimension.Moreover,a novel piecewise-defined function in conjunction with the intraspecific scaling laws was proposed to explain the diverse metabolic scaling in animals and plants.The intraspecific and interspecific scaling laws showed good agreement with morphometric measurements.The experimentally-validated scaling models predict the diversity of intraspecific and interspecific scaling seen in nature.To our knowledge,this is the first study to use fractal models to explain the convex and concave forms of metabolic scaling in animals and plants.The study resolves the long-term controversies to use the resource-transport network models for explanation of the allometric scaling law of metabolism.