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Intracranial aneurysms (ICAs) pose significant health risks, and endovascular coiling remains a widely adopted technique for their treatment. This study investigates the hemodynamic effects of coiling in ICA aneurysms by introducing an equivalent porous condition to simulate realistic coil deployments. The equivalent porous model enables a computationally efficient representation of coil-induced flow alterations without compromising the fidelity of hemodynamic analysis. Using computational fluid dynamics (CFD), we simulate blood flow within aneurysms treated with varying coil densities and configurations to evaluate their impact on flow velocity, wall shear stress and vorticity. The study aims to provide insights into how coil deployment affects intra-aneurysmal hemodynamics, including potential flow stagnation and clot formation. This work presents the evaluated coiling for the real coiling by comparison of the hemodynamic factors of wall shear stress. Our findings demonstrate the validity of the equivalent porous condition for predicting treatment outcomes, offering a valuable framework for optimizing coil design and placement strategies in clinical settings. This work contributes to advancing patient-specific treatment planning and improving therapeutic efficacy for ICA aneurysms.

Arterial stenosis, a narrowing of the artery, significantly impacts blood flow dynamics and heat transfer. Although this phenomenon has been studied broadly, there is very less study about the complex interactions between nonNewtonian blood behavior, complicated artery geometry and temperature fluctuations. Using the Sisko model to represent the nonNewtonian blood nature in a trapezoidally stenotic artery, this study looks to clarify impact of arterial stenosis on blood flow dynamics. This study specifically looks into the temperature, pressure and velocity profiles in these circumstances. A Sisko structural equation-based mathematical model is created to represent blood flow via a trapezoidally stenosed artery. The governing equations which include momentum, energy conservation and continuity are numerically solved with the proper boundary conditions. Under various parametric values, the study shows complex fluctuations in the temperature, pressure and velocity profiles within the stenosed artery. These profiles are greatly impacted by the nonNewtonian conduct of blood, especially in the stenosis zone. It is discovered that the degree of stenosis is important in determining heat transmission, shear stress and flow resistance. Important new information about the hemodynamics and thermal behavior of blood in stenosed arteries is provided by this study. The results increase our understanding of vascular disorders and have the potential to guide the creation of innovative diagnostic and medical techniques.

The lattice Boltzmann formulation on unstructured grids (ULBE) is compared against semi-analytical solutions of non-Newtonian flows in straight channels, as well as with finite-element simulations in stenosed geometries. In all cases, satisfactory agreement is found, lending further credit to the ULBE method as a potentially useful method for the numerical simulation of small-scale hemodynamic flows, such as blood flow in capillaries and arterioles.

We present a lattice Boltzmann (LB) model for the simulation of hemodynamic flows in the presence of compliant walls. The new scheme is based on the use of a continuous bounce-back boundary condition, as combined with a dynamic constitutive relation between the flow pressure at the wall and the resulting wall deformation. The method is demonstrated for the case of two-dimensional (axisymmetric) pulsatile flows, showing clear evidence of elastic wave propagation of the wall perturbation in response to the fluid pressure. The extension of the present two-dimensional axisymmetric formulation to more general three-dimensional geometries is currently under investigation.

Computational modeling plays an important role in biology and medicine to assess the effects of hemodynamic alterations in the onset and development of vascular pathologies. Synthetic analytic indices are of primary importance for a reliable and effective a priori identification of the risk. In this scenario, we propose a multiscale fluid-structure interaction (FSI) modeling approach of hemodynamic flows, extending the recently introduced three-band decomposition (TBD) analysis for moving domains. A quantitative comparison is performed with respect to the most common hemodynamic risk indicators in a systematic manner. We demonstrate the reliability of the TBD methodology also for deformable domains by assuming a hyperelastic formulation of the arterial wall and a Newtonian approximation of the blood flow. Numerical simulations are performed for physiologic and pathologic axially symmetric geometry models with particular attention to abdominal aortic aneurysms (AAAs). Risk assessment, limitations and perspectives are finally discussed.

In this paper, we deploy the hybrid Lattice Boltzmann - Particle Dynamics (LBPD) method to investigate the transport properties of blood flow within arterioles and venules. The numerical approach is applied to study the transport of Red Blood Cells (RBC) through plasma, highlighting significant agreement with the experimental data in the seminal work by Fåhræus and Lindqvist. Moreover, the results provide evidence of an interesting hand-shaking between the range of validity of the proposed hybrid approach and the domain of viability of particle methods. A joint inspection of accuracy and computational cost, indicate that LBPD offers an appealing multiscale strategy for the study of blood transport across scales of motion, from macroscopic vessels, down to arterioles and venules, where particle methods can eventually take over.

The objective of the present study was to evaluate the effect of a six-month Tai Chi (TC) exercise cardiac rehabilitation program on two prognostic factors of cardiac events, rate-pressure product and rate-pressure product reserve, in patients with coronary artery disease (CAD). Patients (N = 54) with CAD were recruited from the clinics of cardiology and cardiovascular surgery at a regional hospital in Taiwan. Twenty-two of them enrolled in the TC rehabilitation program which consisted of weekly 90-min sessions of Yang's style TC for six months in addition to receiving usual care. The remaining 32 patients received usual care only. Modified Bruce treadmill exercise test was performed to evaluate their exercise test responses at baseline and at six months. The change over time was significantly different between the TC and control group in peak rate-pressure product (RPP) (interaction between group and time, p = 0.029) and in RPP reserve (interaction between group and time p = 0.009) over the six-month period, there was a decrease in peak RPP of 32.0 mmHg × bpm × 10^-2 and in RPP reserve of 37.4 mmHg × bpm × 10^-2 in the TC group. In conclusion, participating in a six-month TC exercise-based cardiac rehabilitation program was associated with improved peak RPP and RPP reserve during exercise testing in patients with CAD. TC exercise program may lead to a better prognosis for cardiac events in patients with CAD.

The low-frequency portion of the power spectrum of human heartbeat intervals exhibits a 1/f-like scaling behavior. Despite its clinical significance, the mechanism remains unknown. By recording heartbeat intervals, renal sympathetic nerve activity (SNA), and blood pressure (BP) in conscious rats with normal or high BP, we reported that the scaling slope of heartbeat intervals is steeper in the rats with high BP, and that SNA leads to heartbeat interval and BP changes, and also the dynamics of these three variables, heartbeat intervals, BP, and SNA, results from a low-dimensional chaos. This hemodynamics is modeled excellently by modification of a known chaotic electrical circuit, Chua circuit. Increasing the resistive element between SNA and BP in the circuit increases the scaling slope and abolishes the low-dimensional chaos. Therefore, sensitivity of BP to sympathetic control is likely to determine the scaling slopes of heartbeat intervals in health and disease.

Chaotic models as a rule are based on nonlinear recursive discrete equations, often illustrated by the logistic equation. In this paper, a conjecture is presented that gives an approximate solution to the continuous logistic equation. It is shown that if certain chaotic models are viewed as continuous rather than discrete, the strict borderline mathematical concept of the onset of chaos no longer retains its importance in some practical problems. In fact, it is more important to look at the degree of chaos, as illustrated in two medical problems dealing with blood flow and heart rate variability. The chaotic modeling approach is seen to be useful in analyzing experimental data.

The models of viscoelasticity are considered from the point of view of their applicability to describe the behavior of blood vessel wall material. First, some convenient and popular models are considered briefly. These models are widely used, particularly in engineering applications, because of their simplicity and clear physical treatment. At the same time, these models are not representative of many real (and particularly anatomical) materials. As a result, new nonlinear models have been developed by Fung and other researchers for biomaterials. However before them, one of the generalized model of viscoelasticity has been developed by Knopoff and MacDonald. Here this model is considered and applied for evaluation of blood vessel wall characteristics. Unlike the convenient models, this model is based on fundamental thermodynamic concepts, and takes into account some more realistic features of viscoelastic solids. Application of this model to determine the characteristics of blood vessel material is presented.

The present study deals with an appropriate mathematical model describing blood flow through a constricted artery that is used to analyze the physiological flow field. The time-variant geometry of the arterial segment having an overlapping type of constriction in the arterial lumen — which frequently occurs in diseased arteries, causing flow disorder and leading to malfunction of the cardiovascular system — is framed mathematically. Blood flow contained in the stenosed artery is treated as non-Newtonian (having shear-dependent viscosity) and is considered to be two-dimensional. The motion of the arterial wall and its effect on local fluid mechanics are not ruled out from the present pursuit. The flow analysis applies the time-dependent, two-dimensional incompressible nonlinear Navier–Stokes equations for non-Newtonian fluids. The flow field can be obtained by first transforming radial coordinates with the use of appropriate boundary conditions, and then adopting a suitable finite difference scheme numerically. The unsteady response of the system and the influence of the arterial wall distensibility, the non-Newtonian rheology of blood, and the presence of stenosis on the important aspects of the physiological flow phenomena are quantified in order to indicate the susceptibility to atherosclerotic lesions and thereby validate the applicability of the present theoretical model.

This study extracted hemodynamic information from echocardiogram to complement the left ventricle ejection fraction and the stroke volume for cardiac evaluation and diagnosis. The dynamic characteristics of irregular wall motions can be analyzed by kinetic energy fluxes transferred from the left ventricle to the blood flow. A set of cardiac indices is developed for quantification and classification of echocardiogram for clinical application. The pumping characteristics can be further quantified through the work done by pressure and viscous stresses of the ventricle.

Venous valves and sinuses are frequently observed in vein grafts in the coronary artery bypass grafts (CABG). However, from the biomedical engineering viewpoint, vein grafts are always assumed as smooth tubes in the existing simulations, and no effort has been made to investigate the effects of jaggedness of the graft inner wall due to the valve cusps remnants and valve sinus (in case of valve-stripped saphenous vein (SV) grafts) on the blood flow patterns and hemodynamic parameters (HPs). In this paper, the effects of the inner surface irregularities of a vein graft on the blood flow is investigated in the graft as well as in the distal anastomotic region, with a more realistic geometry of valve-stripped SV, by means of numerical simulation of pulsatile, Newtonian blood flow. The simulation results demonstrate that the valve remnants and sinuses cause disturbances in the flow field within the graft (due to vortices formation within the valve sinuses) and undesirable distribution of HPs, which can result in early atherosclerotic lesion development in the graft.

A novel recursive algorithm was proposed to calculate the input impedance of human systemic arterial tree, and to simulate the human systemic arterial hemodynamics with an 55 segment transmission line model. In calculation of input impedance, the structure of the arterial tree was expressed as a single linked list. An infinitesimal constant was used to replace 0 Hz frequency to calculate the DC and AC part of input impedance simultaneously. The input impedance at any point of the arterial tree can obtain easily by the proposed recursive algorithm. The results of input impedance are in accord with experimental data and other models' results. In addition, some comparisons were conducted about the effects of arterial compliance, length, internal radius and wall thickness on the input impedance of ascending aorta. The results showed input impedances of ascending aorta displayed significantly different characteristics for different kinds of parameters. Finally, the blood pressure and flow waveforms of all arterial segments were calculated and displayed in 3D. The arterial elasticity and viscosity were discussed by changing the Young's modulus and the phase difference, respectively. The simulation results showed that the blood pressure and flow waveforms of the arterial tree reflected accurately the main characteristic features of physiopathological changes, which demonstrated the effectiveness of the proposed model.

Intimal hyperplasia developed at the end-to-side anastomosis of artery bypass is closely related to unphysiological hemodynamics. The helical flow as a normal physiological phenomenon in arteries is beneficial to endothelial damage repair. To deeply understand the physiological flow properties in a S-type bypass (StB) graft, four end-to-side bypass models including 30°, 45°, 60° conventional bypasses and a 45° StB were compared numerically under physiological pulsatile flow. The results showed that strong helical flow was observed at the distal anastomosis of StB. The distribution of hemodynamic parameters such as helicity, average wall shear stress and oscillating shear index, etc. were significantly improved at the S-type anastomosis as compared with those of three conventional models. The area-averaged normalized helicity in StB reached maxima at the moments of maximum flow rate and systolic deceleration. The hemodynamic performance in a 45° StB was improved as compared with a 30° conventional model. It is concluded that large StB anastomosis angle can be taken to achieve good hemodynamic performance while much smaller anastomosis angle has to be adopted for conventional bypass. As such, a S-type anastomosis should be a feasible choice of clinical artery bypass grafting due to its significant improvement in hemodynamic performance.

Stents have been used successfully for treating stenosis in the vertebral artery ostium. The size of stent is found to be an important link in stent design, implantation strategy, and clinical outcome. However, there is no direct evidence of a relationship between stent expansion ratio and the stented artery. This study investigated the influence of stent expansion ratio on local hemodynamics (such as pressure distribution and pressure gradient) of vertebral artery ostial stenosis to determine a possible biomechanical mechanism. Computer-aided design of models with stents with different expansion ratios (i.e., 1.00, 1.125, and 1.25) and internal flow fields were created. All the models were meshed and simulated using computational fluid dynamics (CFD) tools. The comparisons of pressure distribution and pressure gradient are specifically presented. The results showed that the pressures increase and the pressure gradient decreases after stent implantation. The mean pressure at the stented region rises significantly with the increase of stent oversize. The heterogeneity of the pressure gradient was reduced at the stented region in the case with the expansion ratio of 1.125, whereas this effect was not obvious in other expansion ratio cases. Additionally, the combination of higher pressure and a lower pressure gradient in the case with the expansion ratio of 1.125 was significantly observed. This study demonstrated that the proper size of stent, especially with regards to the expansion ratio, is an important factor influencing the treatment of vertebral artery ostial stenosis. It is the recognition of the necessity to consider the relationship between expansion ratio and stenosis in vertebral artery ostium. These findings could help to address the optimization of hemodynamic performance for stent implantation.

The changes of hemodynamics and drug distribution caused by the implantation of drug-eluting stents (DES) have a significant influence on the in-stent restenosis. The present study numerically carried out a comparative study of hemodynamics and drug distribution using four different links of DES: Cordis BX velocity (Model A), Jostent flex (Model B), Sorin Carbostent (Model C), and DT-2 (Model D). The results showed that (1) low wall shear stress (WSS) distribution region spread widely in Model C (16.16%), with the least in Model B (10.35%); (2) Model C has relatively uniform drug concentration and causes of fewer low drug concentration region; and (3) Model A has the largest drug concentration, but also the most uneven distribution of drug. It was concluded that DES with circumferential links helps to improve in-stent restenosis as compared with that with longitudinal designs, and flexible links led to more uniformly and smoothly distributed blood flow than rigid links. However, the links with longitudinal designs had a better performance as drug release carrier than that with circumferential design. And if the links are too close together, the drug cannot be released effectively in the blood vessels. The current study helps to enhance our understanding of the performance of DES and provides assistance for optimal design and selection of DES.

Portal vein thrombosis (PVT) is an important complication that is associated with cirrhotic portal hypertension. The etiology is as yet unclear but could be closely related to the hemodynamics of the portal vein system. This paper investigated the hemodynamics in the portal vein model, both with and without thrombosis, as well as the effect of obstructions on the hemodynamics of the portal vein system using the computational fluid dynamics (CFD) method. PVT can probably develop in the inlets of the portal vein as well as the left/right branches of the portal vein because the distribution of wall shear stress satisfies the conditions for PVT formation based upon the simulation of the hemodynamics in the normal portal vein model. According to the above results, geometric models for a portal vein with a thrombus were constructed and the influence of different degrees (26%, 39%, 53% and 64%) of obstructions was studied. In the model with the maximum obstruction (64% blocked), the maximum velocity of portal vein (PV) increased up to twice than in the model without thrombosis, and the maximum wall shear stress of PV in the model with thrombosis (64% blocked) increased up to 9.4 Pa, whereas it was only 1.9 Pa in the model without thrombosis (nearly one fifth of the maximum wall shear stress). Excessive wall shear stress may cause mechanical damage to the blood vessels and induce physiological changes.

The progression of intimal hyperplasia is considered to be the main cause of bypass failure and is directly related to the individual blood rheology, local arterial geometry and placement of the junctions, graft diameter and graft surface characteristics as well as the degree of compliance. In this paper we use commercial computational fluid dynamics (CFD) ANSYS to examine under the correct physiological flow conditions the hemodynamic forces of composite bypass with internal mammary artery in Y-grafting and consequence grafting which is known to achieve high patency rate and highly recommended by clinicians. Particular emphasis is given here on the parameters that could initiate the development of intimal hyperplasia within these bypass configurations. The hemodynamic flow patterns between the consequence grafting and the composite Y-grafting are observed here to be different. Moreover, on both end-to-side and side-to-side configurations, the circulating flows are detected in the vicinity of the junction area, while the Dean flow vortexes are only observed on the end-to-side configuration. Likewise, the hemodynamic flow on the end-to-side configuration on the LCX of both 45° and 90° Y-grafting is found to be smoother than that of the junction on the LCA, regardless of the changing of anastomosis angles. The high WSS gradients are observed at the vicinity of the toe and on the bed of the junction, while the low WSS are presented at the distal of the stenosis and at the stagnation point. The clinical relevance of the results are presented and discussed with particular focus on the factors and the flow patterns that trigger the development of intimal hyperplasia.

Purpose: Hypoplastic left heart syndrome (HLHS) is a congenital heart disease and is usually associated with pulmonary artery stenosis. The superior vena cava-to-pulmonary artery (bidirectional Glenn) shunt is used primarily as a staging procedure to the total cava-to-pulmonary connection for single-ventricle complex. When HLHS coexists with pulmonary artery stenosis, the surgeons then face a multiple problem. This leads to high demand of optimized structure of Glenn surgery. The objective of this article is to investigate the influence of various anastomotic structures and the direction of superior vena cava (SVC) in Glenn on hemodynamics under pulse inflow conditions and try to find an optimal structure of SVC in Glenn surgery with unilateral pulmonary artery stenosis.

Method: First, 3D patient-specific models were constructed from medical images of a HLHS patient before any surgery by using the commercial software Mimics, and another software Free-form was used to deform the reconstructed models in the computer. Four 3D patient-specific Glenn models were constructed: model-1 (normal Glenn), model-2 (lean the SVC back to the stenotic pulmonary artery), model-3 (lean the SVC towards the stenotic pulmonary artery), model-4 (add patch at junction of the SVC toward stenosis at pulmonary artery). Second, a lumped parameter model (LPM) was established to predict boundary conditions for computational fluid dynamics (CFD). In addition, numerical simulations were conducted using CFD through the finite volume method. Finally, hemodynamic parameters were obtained and evaluated.

Results: It was showed that model-4 have relatively balanced vena cava blood perfusion into the left pulmonary artery (LPA) and right pulmonary artery (RPA), this may be due to less helical flow and the patch at junction of the SVC. Near stenosis of pulmonary artery, model-4 performed with the higher wall shear stress (WSS), which would benefit endothelial cell function and gene expression. In addition, results showed that model-4 performed with the lower oscillatory shear index (OSI) and wall shear stress gradient (WSSG), which would decrease the opportunity of vascular intimal hyperplasia.

Conclusion: It is benefited that surgeons adds patch at junction of the SVC towards stenosis at pulmonary artery. These results can impact the surgical design and planning of the Glenn surgery with unilateral pulmonary artery stenosis.