Computational modelling of blood flow through curved stenosed arteries

Numerical investigation of quantitative pulmonary pressure ratio in different degrees of stenosis

BACKGROUND

Pulmonary artery stenosis endangers people's health. Quantitative pulmonary pressure ratio (QPPR) is very important for clinicians to quickly diagnose diseases and develop treatment plans.

OBJECTIVE

Our purpose of this paper is to investigate the effects of different degrees (50% and 80%) of pulmonary artery stenosis on QPPR.

METHODS

An idealized model is established based on the normal size of human pulmonary artery. The hemodynamic governing equations are solved using fluid-structure interaction.

RESULTS

The results show that the QPPR decreases with the increase of stenosis degree, and it is closely related to the pressure drop at both ends of stenosis. Blood flow velocity and wall shear stress are sensitive to the stenosis degree. When the degree of stenosis is 80%, the amplitude of changes of blood flow velocity and wall shear stress at both ends of stenosis is lower.

CONCLUSIONS

The results suggest that the degree of pulmonary artery stenosis has a significant impact on QPPR and hemodynamic changes. This study lays a theoretical foundation for further study of QPPR.

Numerical analysis of hemodynamics in pulmonary artery stenosis

BACKGROUND: Pulmonary artery stenosis is a serious threat to people’s life and health. OBJECTIVE: The hydrodynamic mechanism of pulmonary artery stenosis is investigated. METHODS: Numerical analysis of hemodynamics in pulmonary artery stenosis using computational fluid dynamics techniques is a well-established method. An idealized model of pulmonary stenosis is established, and the model is divided into main pulmonary artery, right and left pulmonary arteries, and their branches. The sections at different positions are intercepted to study the distribution trend of maximum velocity, pressure and wall shear stress. RESULTS: The numerical simulation results show that the pressure drop at both ends of the narrow is large. High velocity and wall shear stress exist in the center of stenosis, and the wall shear stress at the distal end of stenosis gradually decreases, resulting in endothelial dysfunction. CONCLUSIONS:  To some extent, this study helps clinicians make diagnosis and treatment plans in advance and improve prognosis. This method could be used in the numerical simulation of practical models.

Numerical simulation of pulsatile blood flow characteristics in a multi stenosed coronary artery

BACKGROUND

Coronary artery disease is reported as one of the most common sources of death all over the world. The presence of stenosis (plaque) in the coronary arteries results in the restriction of blood supply, which leads to myocardial infarction.

OBJECTIVE

The aim of this study was to investigate the effect of multi stenosis on hemodynamics parameters in idealized coronary artery models with varying degrees of stenosis and interspace distance between the stenosis.

METHODS

A finite volume-based software package (Ansys CFX version 17.2) was employed to model the blood flow. The hemodynamic stenosis parameters of blood, such as the pressure, velocity, and wall shear stress were obtained.

RESULTS

The computed results showed that the pressure drop is maximum across the 90% area stenosis (AS). The pressure drop is increased as the distance between the proximal and distal stenosis is decreased across the proximal stenosis for the model P70_D70 during the systolic period of the cardiac cycle. A recirculation zone is formed behind the stenosis and is restricted by the occurrence of distal stenosis as the interspacing distance decreases, which could lead to further progression of stenosis in the flow-disturbed area. The wall shear stress was found to increase as the distance between the proximal and distal stenosis is increased across the distal stenosis. The maximum wall shear stress was found at 90% AS.

CONCLUSIONS

In the clinical diagnosis, an overestimation of distal stenosis severity could be possible. Furthermore, the low wall shear stress zone in between the proximal and distal stenosis may help atherosclerotic growth or merge adjacent stenosis.

Numerical investigation of unsteady pulsatile Newtonian/non-Newtonian blood flow through curved stenosed arteries

A numerical investigation of Newtonian/non-Newtonian unsteady pulsatile entry blood flow inside a 3D curved stenosed artery is presented. For considering the non-Newtonian effect (shear thinning or shear thickening behavior), the blood viscosity is characterized by the power-law model (Ostwald de Waele Equation). At the inlet of the artery, a realistic pulsatile waveform is utilized according to the experimental data reported by other researchers. This study belongs to the analysis of the curvature ratios, percentage and length ratio of stenosis, and blood thickening on hemodynamic characteristics of the flow. The results emphasize that the maximum wall shear stress happens near the stenosis neck and as expected, by decreasing the stenosis length, the maximum value of wall shear stress increases. In addition, the results indicate that the shear thickening fluid shows a more stable velocity profile rather than the shear thinning fluid flow.

The influence of artery wall curvature on the anatomical assessment of stenosis severity derived from fractional flow reserve: a computational fluid dynamics study

This study aims to investigate the influence of artery wall curvature on the anatomical assessment of stenosis severity and to identify a region of misinterpretation in the assessment of per cent area stenosis (AS) for functionally significant stenosis using fractional flow reserve (FFR) as standard. Five artery models of different per cent AS severity (70, 75, 80, 85 and 90%) were considered. For each per cent AS severity, the angle of curvature of the arterial wall varied from straight to an increasingly curved model (0°, 30°, 60°, 90° and 120°). Computational fluid dynamics was performed under transient physiologic hyperemic flow conditions to investigate the influence of artery wall curvature on the pressure drop and the FFR. The findings in this study may be useful in in vitro anatomical assessment of functionally significant stenosis. The FFR decreased with increasing stenosis severity for a given curvature of the artery wall. Moreover, a significant decrease in FFR was found between straight and curved models discussed for a given severity condition. These findings indicate that the curvature effect was included in the FFR assessment in contrast to minimum lumen area (MLA) or per cent AS assessment. The MLA or per cent AS assessment may lead to underestimation of stenosis severity. From this numerical study, an uncertainty region could be evaluated using the clinical FFR cutoff value of 0.8. This value was observed at 81.98 and 79.10% AS for arteries with curvature angles of 0° and 120° respectively. In conclusion, the curvature of the artery should not be neglected in in vitro anatomical assessment.

Effect of geometrical assumptions on numerical modeling of coronary blood flow under normal and disease conditions

Shear stress plays a pivotal role in pathogenesis of coronary heart disease. The spatial and temporal variation in hemodynamics of blood flow, especially shear stress, is dominated by the vessel geometry. The goal of the present study was to investigate the effect of 2D and 3D geometries on the numerical modeling of coronary blood flow and shear stress distribution. We developed physiologically realistic 2D and 3D models (with similar geometries) of the human left coronary artery under normal and stenosis conditions (30%, 60%, and 80%) using PROE (WF 3). Transient blood flows in these models were solved using laminar and turbulent (k-ω) models using a computational fluid dynamics solver, FLUENT (v6.3.26). As the stenosis severity increased, both models predicted a similar pattern of increased shear stress at the stenosis throat, and in recirculation zones formed downstream of the stenosis. The 2D model estimated a peak shear stress value of 0.91, 2.58, 5.21, and 10.09 Pa at the throat location under normal, 30%, 60%, and 80% stenosis severity. The peak shear stress values at the same location estimated by the 3D model were 1.41, 2.56, 3.15, and 13.31 Pa, respectively. The 2D model underestimated the shear stress distribution inside the recirculation zone compared with that of 3D model. The shear stress estimation between the models diverged as the stenosis severity increased. Hence, the 2D model could be sufficient for analyzing coronary blood flow under normal conditions, but under disease conditions (especially 80% stenosis) the 3D model was more suitable.

Assessment of blood volume flow in slightly curved arteries from a single velocity profile

Non-invasive estimation of arterial blood volume flow (BVF) has become a central issue in assessment of cardiovascular risk. Poiseuille and Womersley approaches are commonly used to assess the BVF from centerline velocity, but both methods neglect the influence of curvature. Based on the assumption that the velocity in curved tubes as function of the circumferential position for a given radial position can be approximated by a cosine, the BVF can also be estimated by averaging velocities at opposite radial positions, referred to as the cosine theta model (CTM). This study investigates the accuracy of BVF estimation in slightly curved arteries for BVF waveforms obtained in the brachial artery of 6 volunteers. Computational fluid dynamics simulations were used to compute the influence of curvature on velocity profiles. The BVF was then estimated from the simulation results with the CTM and methods based on Poiseuille, Womersley and using the center stream velocity and the velocity waveform at the position where the maximum velocity is observed, and compared to the prescribed BVF. The simulations show that the influence of curvature is strongest when the flow decelerates. For Poiseuille and Womersley, the time average BVF was underestimated by maximally 10.4% and 7.8% for a radius of curvature of 50 and 100 mm, respectively. The estimation error is lower for the CTM and equals 4.2% and 1.2% for a radius of curvature of 50 and 100mm, respectively. From this study, we can conclude that the velocity waveform at the position of the maximum rather than the center stream velocity waveform combined with the Womersley method should be chosen. The CTM improves current estimation techniques if in-vivo velocity distributions are available.

Four-dimensional analysis of cyclic changes in coronary artery shape

The objective of this study was to derive a method for quantifying the dynamic geometry of coronary arteries. Coronary artery geometry plays an important role in atherosclerosis. Coronary artery geometry also influences the performance of coronary interventions. Conversely, implantation of stents may alter coronary artery geometry. Clinical tools to define vessel shape have not been readily available. Using a Frenet-Serret curvature analysis applied to 3D reconstruction data derived from standard coronary angiograms, 21 coronary arteries were analyzed at end-diastole (ED) and end-systole (ES). Vessels were divided anatomically: type 1 consisted of vessels lying in the AV groove (left circumflex, right coronary) and type 2 consisted of vessels overlying actively contracting myocardium (left anterior descending, diagonal, obtuse marginal, right ventricular marginal, posterior descending, posterolateral). Vessel segments were analyzed by assessing the changes in curvature, torsion, and discrete flexion points (FPs), areas of systolic bending in the arterial contour. The curvature from ED to ES of type 1 vessels was unchanged (-0.02 +/- 0.03 cm(-1)), while the curvature change of type 2 vessels showed a 38% increase (0.33 +/- 0.04 cm(-1); P < 0.001). Type 1 vessels had fewer FPs per vessel than type 2 vessels (0.38 +/- 0.18 and 2.40 +/- 0.23 FP/vessel, respectively; P < 0.001). FPs were more common in distal segments and branch vessels. A method to quantify cyclic changes in coronary artery shape was applied to 3D data sets derived from standard coronary angiograms. Coronary arteries undergo a cyclic change in shape resulting in changes in overall curvature as well as formation of discrete flexion points. These changes in vessel shape are asymmetrically distributed in coronary arteries.