Effect of asymmetry on the flow behavior in an idealized arterial bifurcation

Influence of Wavy Arteries and Veins on Hemodynamic Characteristics: A Numerical Study

The present work is focused on the study of hemodynamic characteristics for tortuous arteries/veins. Tortuosity in arteries/veins is defined by introducing waviness in the wall of the tube. Analysis is further extended for bifurcated veins with and without wavy walls. Waviness is defined by two geometric parameters; pitch and depth of the wave. Four different combinations of pitch and depth are studied and compared with a plain straight wall. The present study is carried out numerically by using a computational fluid dynamics tool. Hemodynamics for a steady flow of blood is investigated through pressure, velocity, and wall shear stress distribution. Waviness in the wall of arteries/veins creates a recirculation zone at the crest and trough of the wall. Occurrence of the recirculation zone leads to reduction in velocity which in turn reduces wall shear stress. Variation in the magnitude of the velocity and corresponding wall shear stress at the crest and trough of the wavy wall depends on the pitch and depth of the artery/veins (tube).

Numerical computation of pulsatile hemodynamics and diagnostic concern of coronary bifurcated artery flow for Newtonian and non-Newtonian fluid

Atherosclerotic with the high occurrence of plaque formation due to stenosis has attracted wide attention among researchers. The left coronary artery has been studied in two-dimensional and in three-dimensional (3D) bifurcation as the models of blood flow through Newtonian and non-Newtonian fluids to better understand the physical mechanism. The computational Fluid Dynamics (CFD) technique is incorporated in COMSOL Multiphysics and then it is justified by satisfactory validation. It is found that the Newtonian model shows larger recirculation zones than non-Newtonian does. The present study also focuses on the evaluations of the lesion of diagnostic and the coefficient of pressure drop assessments on the basis of the diagnostic parameter's critical values affected by the rheological model. Nevertheless, the leading concentration of the subsisting investigation works is confined to the change of importance factor (IFc) affected by arterial blockage. But the IFc of non-Newtonian fluid for 3D left coronary artery bifurcation model decreases with increasing bifurcation angle and the time-averaged inlet pressure is the least for smaller bifurcation angles. The current research further concentrates that the flow separation length reduces with developing bifurcation angle in bifurcated geometry. It is significant to mention that non-Newtonian blood flow model incorporating hemodynamic and diagnostic parameters has great impacts on instantaneous flow systems.

Hemodynamic simulation of abdominal aortic aneurysm on idealised models: Investigation of stress parameters during disease progression

BACKGROUND AND OBJECTIVE

Analysis and prediction of rupture risk of abdominal aortic aneurysms (AAA) facilitates planning for surgical interventions and assessment of plausible treatment modalities. Present approach of using maximum diameter criterion, is giving way to hemodynamic and bio-mechanical based predictors in conjunction with Computational fluid dynamic (CFD) simulations. Detailed studies on hemodynamic and bio-mechanical parameters at the stage of maximum growth/rupture is of practical importance to the clinical community. However, understanding the changes in these parameters at different stages of growth, will be useful for clinicians, in planning routine monitoring to reduce the risk of sudden rupture. This is particularly useful in medical resource starved nations. Present study investigates the hemodynamic and bio-mechanical changes occurring during the growth stages of aortic aneurysms using fluid structure interaction (FSI) studies.

METHOD

Six idealized fusiform aneurysm models spanning high (shorter) and low (longer) values of the shape index (DHr), have been analysed at three different stages of growth viz, a D_max of 3.5cm, 4.25cm, 5cm. Pulsatile Newtonian blood flow, passing through an elastic arterial vessel wall with uniform thickness is assumed. Two-way coupled fluid structure interaction have been employed for the numerical simulation of blood flow dynamics and arterial wall mechanics.

RESULTS

Wall shear stress (WSS) parameters and vonmises stress indicators, co-relating rupture and thrombus formation, have been extracted and reported, at each growth stage. When the aneurysm progresses in diameter, the areas recording abnormally low TAWSS, as well as areas of high/low OSI were found to increase at different rates for shorter and longer aneurysms. Moreover, drastic increase in the maximum wall stresses (MWS) and wall displacement were observed as the aneurysm approached the critical diameter.

CONCLUSION

Hemodynamic predictors were found to be highly dependent on the shape index (DHr), when the aneurysm was small, whereas significant influence of DHr on the wall stresses happens, as the aneurysm approaches the critical diameter. Inconsistent variation of these indicators exhibited by shorter aneurysms (high DHr) at different growth stages, demands routine monitoring (using scans), of such aneurysms, to prevent unexpected rupture.

Hemodynamic study in 3D printed stenotic coronary artery models: experimental validation and transient simulation

Atherosclerosis is a progressive disease that can significantly reduce blood supply to vital organs, being one of the main causes of death worldwide. In this work, a numerical and experimental study in 3D printed stenotic coronary arteries, considering both steady and pulsatile blood flow conditions, is presented. The results revealed that a degree of stenosis superior to 50% creates disturbed flows downstream of the contraction, with an accented increase in the wall shear stress measurements at the stenosis throat. Finally, the multiphase mixture was investigated and compared with a single-phase modelling, and only slight differences were observed right after the stenosis throat.

Numerical study of hemodynamic and diagnostic parameters affected by stenosis in bifurcated artery

Stenosis in the bifurcated coronary artery has attracted wide attention among the researchers. Many investigations have been carried out by means of Computational Fluid Dynamics (CFD) to better understand the physical mechanism inside the stenotic bifurcated artery. However, the main focus of the existing publications is limited to the variation of hemodynamic parameters affected by the stenosis and bifurcation structure. The present study aims to make further evaluations of stenosis development and diagnostic lesion assessments based on the critical values of hemodynamic and practical diagnostic parameters. The bifurcated coronary artery with initial stenosis source has been studied in 2 D unsteady model. Different locations of initial stenosis source have been found to greatly affect the orientation of the further stenosis development. In addition, different stenosis severities (diameter stenosis: 30%, 50% and 70%), different stenosis lengths (3 mm, 6 mm and 9 mm) and different pulse rates (75 bpm, 100 bpm and 120 bpm) as controlling parameters have been investigated.