Effect of the biochemical composition of the wall of the vessels of the human thigh on its mechanical properties

The principal characteristics of the mechanical properties of the walls of the human femoral artery and great saphenous vein and their variation with age have been experimentally determined. Macroscopic and microscopic analyses have revealed characteristic age-related changes in the artery and vein walls. The concentrations of six principal biochemical components of the vessel walls have been determined for each age group and the rank correlation coefficients for the principal mechanical properties and biochemical components have been analyzed.Institute of Polymer Mechanics, Academy of Sciences of the Latvian SSR, Riga; Riga Institute of Traumatology and Orthopedics. Translated from Mekhanika Polimerov, No. 2, pp. 316–327, March–April, 1974.     

Determination of the optical density of human coronary arterial walls

Conclusions 1. The greatest thickness is found for the segment of a coronary artery adjacent to the myocardium; this effect is observed even in a neonate.2. At a young age, the greatest thickness is found for the middle and outer wall layers of both coronary arteries.3. In individuals reaching age 40 and having atherosclerosis of the major branches of the cardiac arteries, the walls of both coronary arteries become thicker due to the inner and middle layers, but the thickening of the individual layers is most pronounced in the wall of the left coronary artery.4. The method of optical densitometry relative to stained histological sections of the vascular wall may be used for the relative determination of the densities of tissues and their distributions over the individual wall layers.5. The optical density of elastic tissue of the walls of the coronary arteries reaches a maximum in the third decade of life in the human and decreases after age 40 (especially in the distal segment of the left coronary artery).6. The optical density of the total connective tissue in the walls of the left coronary artery increases with increasing age, especially in the distal segment of this artery. In youth, the optical density of connective tissue is greater in the wall of the right coronary artery, but with increasing age this density decreases markedly.Institute of Polymer Mechanics, Academy of Sciences of the Latvian SSR, Riga. Translated from Mekhanika Polimerov, No. 2, pp. 312–318, March–April, 1978.     

Effect of age on the mechanical properties and biochemical composition of human cardiac arteries

Conclusions 1. The human left coronary arterial wall in subjects from age 15 to 28 has better deformative properties than the right artery.2. With increasing age, a worsening of mechanical properties of the walls is observed specifically for the left coronary artery in comparison with the right coronary artery.3. Quantitative biochemical analysis of the major components of the connective tissue of the human coronary arteries (fibrillar and nonfibrillar proteins and glycoproteins) also disclosed differences among the age groups and the position of the artery (left or right).4. As a result of a dispersion analysis carried out by computer, it was found that both age and position of the artery have a significant effect on the elastin content in the arterial wall and only the age of the subject has a significant effect on the contents of collagen, tyrosine, and hexuronic acids.5. Neither age nor type of artery have a significant effect on the contents of arginine, hexosamines, and hexoses in the arterial wall.Institute of Polymer Mechanics, Academy of Sciences of the Latvian SSR, Riga. Riga Scientific-Research Institute of Traumatology and Orthopedics. Translated from Mekhanika Polimerov, No. 3, pp. 502–506, May–June, 1978.     

Change in several mechanical properties of human blood vessels with aging

A method is suggested for the determination of the initial length of a sample of a blood vessel wall at a longitudinal loading. It was found that at loading levels of up to 0.01 kg/mm², the deformation properties of the wall of a large subcutaneous vein and femoral artery differ inappreciably, but on further loading substantial differences were observed between the deformation and strength properties of the walls of vessels.     

Rheological properties of the human great saphenous vein in normal subjects and in the presence of varicose conditions

The "quasiequilibrium" and certain relaxation properties of the material of the wall of the human great saphenous vein have been experimentally determined, and the differences for two age groups and for subjects with varicose conditions have been established. The relation between the rheological characteristics of the vein wall and its histological structure is discussed.     

Non-linear peristaltic transport in an inclined asymmetric channel

The problem of peristaltic transport of a hydromagnetic (electrically conducting) viscous incompressible fluid in an inclined planar channel having electrically insulated walls has been investigated under long-wavelength and low-Reynolds number assumptions. The channel asymmetry is produced by choosing the peristaltic wave train on the walls to have different amplitudes and phase. The flow is investigated in a wave frame of reference moving with the velocity of the wave. Expressions for velocity field, shear stress and pressure gradient on the wall are obtained. The effects of different parameters entering into the problem are discussed numerically and explained graphically.     

Power law fluid model for blood flow through a tapered artery with a stenosis

In the present paper, blood flow through a tapered artery with a stenosis is analyzed, assuming the flow is steady and blood is treated as non-Newtonian power law fluid model. Exact solution has been evaluated for velocity, resistance impedance, wall shear stress and shearing stress at the stenosis throat. The graphical results of different types of tapered arteries (i.e. converging tapering, diverging tapering, non-tapered artery) have been examined for different parameters of interest. Some special cases of the problem are also presented.     

主动脉弓及分支血管内非稳态血流分析

运用流体力学中的三维非定常Navier-Stokes方程作为血液流动的控制方程,并采用计算流体力学方法对人体主动脉弓及分支血管内非Newton(牛顿)血液黏度模型下血流进行瞬态数值模拟.分析了一个心动周期内不同时刻血流动力学特征参数的分布对动脉粥样硬化斑块形成的影响,并与Newton血液黏度模型下的血管壁面压力和壁面切应力特征参数进行对比.结果表明:与Newton血液模型相比,非Newton血液模型下血流分布更符合真实血流特性;在心动收缩期,分支血管外侧壁附近存在面积较大的低速涡流区,该区域内血管壁面压力与壁面切应力具有较大的变化量,血液中的血小板、脂质和纤维蛋白等易沉积,血管内壁易疲劳损伤并发生血管重构,促使动脉粥样硬化斑块形成;而在心动舒张期,分支血管内血流速度分布均匀,血管壁面压力与壁面切应力变化量较小,血管壁受到较小的应力作用,对动脉粥样硬化斑块形成的作用较小.     

肾动脉变窄和流-固结构相互作用对非Newton脉动流的影响——一个真实的腹部主动脉和肾动脉模型

研究肾动脉狭窄(RAS)对血液流动和血管壁的影响.根据CT扫描图像,重建腹部主动脉和肾动脉的解剖模型,通过模型的脉动流进行了仿真计算,计算中考虑了流体-固体结构的相互作用(FSI).研究RAS对血管壁剪切应力和位移的影响,RAS使得肾动脉中流量减少,肾素-血管紧缩素系统可能被激活,从而导致严重的高血压.     

A new model for study the effect of wall properties on peristaltic transport of a viscous fluid

The present study extends the two-dimensional analysis of peristaltic motion to include a compliant wall. The fluid-solid interaction problem is investigated by considering equations of motion of both the fluid and the deformable boundaries. The driving mechanism of the muscle is represented by assuming the channel walls to be compliant. A perturbation solution of the stream function for zeroth, first and second order in a small amplitude ratio is obtained. The phenomenon of the “mean flow reversal” is found to exist both at the center and at the boundaries of the channel. The effect of wall damping, wall elastance and wall tension on the mean axial velocity and reversal flow has been investigated. The numerical results show that the possibility of flow reversal increases by increasing the wall damping and decreases by increasing the wall elastance and wall tension.     

Heat transfer in channel flow of a micropolar fluid

The study of heat transfer in channel flow has been done by previous authors for Newtonian and elastico-viscous fluids. It is the aim of the present paper to study the temperature profile for flow of a micropolar fluid in a channel induced by a constant axial pressure gradient, when the walls are maintained at constant temperatures. We have examined the effects of microrotation on the temperature profile and on the kinetic energy of the fluid. Three cases have been chosen by us for detailed study: (i) both the walls are maintained at different constant temperatures, (ii) both the walls are maintained at the same constant temperature, (iii) one wall is kept at a constant temperature and there is no heat flux at the other wall.     

Model of vascular tonus

The use of the general theory of the mechanics of muscle tissue for constructing a simplified model describing the mechanical behavior of a blood vessel wall containing muscle layers is dicussed. A formalization of the concept of tonus is proposed and the activator concentration in the myofibrils is introduced as a measure of that characteristic. The properties of vessels having a static characteristic with a descending branch are considered, particular attention being given to the case where the descending branch is associated with a strong dependence of the tonus on the state of stress of the vessel wall.     

Artificial stenoses for computational hemodynamics

Atherosclerosis is a major cause of death in developed countries. Mass accumulation in artery walls causes obstruction to the blood flow, stenoses, giving origin to life threatening events. This work focuses on the use of a simple and effective methodology for creating three-dimensional irregular stenosis in artery models for numerical and in vitro hemodynamic studies. The method infers the artery location prone to stenoses appearance by identifying areas of low wall shear stress. Then, by using a diffusional process, irregular shaped stenoses are artificially created. This simple diffusional process mimics aspects of the growth of stenoses, such as the growth rate dependence of a time dependent flux. The method was demonstrated using different artery models, one of them being taken from a healthy patient CT scan. The generated stenoses are irregularly shaped and are highly dependent on the flow patterns developed in each artery type. The method disclosed allows a fast hemodynamic comparison between healthy and a stenotic case for a given artery geometry.     

Pulsatile flow of Herschel–Bulkley fluid through catheterized arteries – A mathematical model

The pulsatile flow of blood through catheterized artery has been studied in this paper by modeling blood as Herschel–Bulkley fluid and the catheter and artery as rigid coaxial circular cylinders. The Herschel–Bulkley fluid has two parameters, the yield stress θ and the power index n. Perturbation method is used to solve the resulting quasi-steady nonlinear coupled implicit system of differential equations. The effects of catheterization and non-Newtonian nature of blood on yield plane locations, velocity, flow rate, wall shear stress and longitudinal impedance of the artery are discussed. The existence of two yield plane locations is investigated and their dependence on yield stress θ, amplitude A, and time t are analyzed. The width of the plug core region increases with increasing value of yield stress at any time. The velocity and flow rate decrease, whereas wall shear stress and longitudinal impedance increase for increasing value of yield stress with other parameters held fixed. On the other hand, the velocity, flow rate and wall shear stress decrease but resistance to flow increases as the catheter radius ratio (ratio of catheter radius to vessel radius) increases with other parameters fixed. The results for power law fluid, Newtonian fluid and Bingham fluid are obtained as special cases from this model.     

Significance of plaque morphology in modifying flow characteristics in a diseased coronary artery: Numerical simulation using plaque measurements from intravascular ultrasound imaging

The paper deals with numerical investigation of the effect of plaque morphology on the flow characteristics in a diseased coronary artery using realistic plaque morphology. The morphological information of the lumen and the plaque is obtained from intravascular ultrasound imaging measurements of 42 patients performed at Cleveland Clinic Foundation, Ohio. For this data, study of Bhaganagar et al. (2010) [1] has revealed the stenosis for 42 patients can be categorized into four types – type I (peak-valley), type II (ascending), type III (descending), and type IV (diffuse). The aim of the present study is to isolate the effect of shape of the stenosis on the flow characteristics for a given degree of the stenosis. In this study, we conduct fluid dynamic simulations for the four stenosis types (type I–IV) and analyze the differences in the flow characteristics between these types. Finely refined tetrahedral mesh for the 3-D solid model of the artery with plaques has been generated. The 3-D steady flow simulations were performed using the turbulence (k–ε) model in a finite volume based computational fluid dynamics solver. The axial velocity, the radial velocity, turbulence kinetic energy and wall shear stress profiles of the plaque have been analyzed. From the axial and radial velocity profiles results the differences in the velocity patterns are significantly visible at proximal as well as distal to the throat, region of maximum stenosis. Turbulent kinetic energy and wall shear stress profiles have revealed significant differences in the vicinity of the plaque. Additional unsteady flow simulations have been performed to validate the hypothesis of the significance of plaque morphology in flow alterations in diseased coronary artery. The results revealed the importance of accounting for plaque morphology in addition to plaque height to accurately characterize the turbulent flow in a diseased coronary artery.     

Starting solutions for oscillating motions of an Oldroyd-B fluid over a plane wall

In this paper, we establish the starting solutions for oscillating motions of an Oldroyd-B fluid between two side walls perpendicular to a plane wall. The expressions for the velocity field and the associated tangential stress at the bottom wall are obtained, presented under integral and series form. These satisfy all imposed initial and boundary conditions. The obtained solutions are graphically analyzed for the variations of interesting flow parameters. In the absence of side walls, all solutions that have been obtained reduce to those corresponding to the motion over an infinite plate. Moreover, the obtained solutions can be specialized to give similar solutions for Maxwell, second grade and Newtonian fluids performing the same motions.     

Mathematical modeling of pulsatile flow of non-Newtonian fluid in stenosed arteries

The pulsatile flow of blood through mild stenosed artery is studied. The effects of pulsatility, stenosis and non-Newtonian behavior of blood, treating the blood as Herschel–Bulkley fluid, are simultaneously considered. A perturbation method is used to analyze the flow. The expressions for the shear stress, velocity, flow rate, wall shear stress, longitudinal impedance and the plug core radius have been obtained. The variations of these flow quantities with different parameters of the fluid have been analyzed. It is found that, the plug core radius, pressure drop and wall shear stress increase with the increase of yield stress or the stenosis height. The velocity and the wall shear stress increase considerably with the increase in the amplitude of the pressure drop. It is clear that for a given value of stenosis height and for the increasing values of the stenosis shape parameter from 3 to 6, there is a sharp increase in the impedance of the flow and also the plots are skewed to the right-hand side. It is observed that the estimates of the increase in the longitudinal impedance increase with the increase of the axial distance or with the increase of the stenosis height. The present study also brings out the effects of asymmetric of the stenosis on the flow quantities.     

流固耦合作用下狭窄颈动脉内非Newton血流分析

采用计算流体力学方法分别对6种狭窄率的颈动脉内非Newton瞬态血流进行流固耦合数值分析.研究了狭窄率对颈动脉内血流动力学分布的影响,以探索狭窄率与颈动脉内粥样斑块形成的关系.结果表明,狭窄率不同的颈动脉内血流动力学分布特性明显不同,与0.05,0.1,0.2,0.3和04这5种狭窄率的颈动脉内血流动力学分布特性相比,狭窄率为0.5的颈动脉内血流动力学分布独特,狭窄部位附近区域存在面积较大的低速涡流区;复杂血流作用下,该区域分布低壁面压力,异常壁面切应力,较大管壁形变量和von Mises应力;血流速度低使血液中脂质、纤维蛋白等大分子易沉积,低壁面压力引起的明显“负压”效应引发脑部供血障碍,异常壁面切应力作用下粥样斑块易破裂与脱落,并堵塞脑血管,较大的von Mises应力易引起应力集中,导致血管破裂,为脑卒中发生提供有利条件.因此,狭窄率越大对颈动脉内血流动力学分布的影响越显著,促进颈动脉粥样斑块形成与发展,并引发缺血性脑卒中.     

Three-dimensional numerical simulation of blood flow in mouse aortic arch around atherosclerotic plaques

Atherosclerosis is a progressive disease, involving the build-up of lipid streaks in artery walls, leading to plaques. Understanding the development of atherosclerosis and plaque vulnerability is critically important since plaque rupture can result in heart attack or stroke. Plaques can be divided into two distinct types: those likely to rupture (vulnerable) or less likely to rupture (stable). In the last decade, researchers have been interested in studying the influence of the mechanical effects (blood shear stress, pressure forces and structural stress) on the plaque formation, progression and rupture processes but no general agreement has been found. The purpose of the present work is to include more realistic conditions for the numerical calculations of the blood flow by implementing real geometries with plaques in the numerical model. Hemodynamical parameters are studied in both diseased and healthy configurations. The healthy configuration is obtained by removing numerically the plaques from three dimensional geometries obtained by micro-computed tomography. A new hemodynamical parameter is also introduced to relate the location of plaques to the characteristics of the flow in the healthy configuration.     

On the plane couette flow of a variable viscosity fluid

In the present paper the Plane Couette flow for three cases, (i) Walls at unequal temperatures, (ii) Walls at equal temperatures and (iii) One of the walls is insulated, has been studied by taking a non-linear relation between viscosity and temperature. Exact solutions of the conpled momentum and energy equations have been obtained. A modified law for the transfer of heat at the upper wall is found in the case of unequal wall temperatures.