A seepage outlet boundary condition in hemodynamics modeling

Numerical simulation of hemodynamics in patient-specific pulmonary artery stenosis

BACKGROUND

The incidence rate of pulmonary artery stenosis is increasing year by year and its numerical simulation has become a key project of biomedical engineering.

OBJECTIVE

The purpose of this work is to study the changes of hemodynamic parameters in patient-specific pulmonary artery stenosis.

METHODS

A pulmonary artery stenosis model is established based on patient-specific computed tomography (CT) images. According to the actual anatomy of patient-specific pulmonary artery stenosis, the stenosis area is simulated using a porous medium to study its hemodynamic changes. The computational fluid dynamics (CFD) method is used to simulate the hemodynamic changes of pulmonary artery stenosis, and to explore the mechanical characteristics between blood flow and vessel wall.

RESULTS

The results suggest that the blood pressures of arterial branches increase and the pressure drop at both ends of the stenosis is higher. There is a high flow rate and wall shear stress at the stenosis.

CONCLUSION

This study shows that the hemodynamic model of pulmonary artery stenosis can be accurately reconstructed by achieving numerical simulation of the local stenosis through CT images, and this work has important implications for improving the confidence of clinical diagnosis and treatment of pulmonary artery diseases.

Numerical modeling in arterial hemodynamics incorporating fluid-structure interaction and microcirculation

Background

The effects of arterial wall compliance on blood flow have been revealed using fluid-structure interaction in last decades. However, microcirculation is not considered in previous researches. In fact, microcirculation plays a key role in regulating blood flow. Therefore, it is very necessary to involve microcirculation in arterial hemodynamics.

Objective

The main purpose of the present study is to investigate how wall compliance affects the flow characteristics and to establish the comparisons of these flow variables with rigid wall when microcirculation is considered.

Methods

We present numerical modeling in arterial hemodynamics incorporating fluid-structure interaction and microcirculation. A novel outlet boundary condition is employed to prescribe microcirculation in an idealised model.

Results

The novel finding in this work is that wall compliance under the consideration of microcirculation leads to the increase of wall shear stress in contrast to rigid wall, contrary to the traditional result that wall compliance makes wall shear stress decrease when a constant or time dependent pressure is specified at an outlet.

Conclusions

This work provides the valuable study of hemodynamics under physiological and realistic boundary conditions and proves that wall compliance may have a positive impact on wall shear stress based on this model. This methodology in this paper could be used in real model simulations.

Influence of microcirculation load on FFR in coronary artery stenosis model

BACKGROUND

The coronary artery hemodynamics are impacted by both the macrocirculation and microcirculation. Whether microcirculation load impact the functional assessment of a coronary artery stenosis is unknown. The purpose of this study is to investigate the effect of porous media of the microcirculation on fractional flow reserve (FFR) in stenotic coronary artery model.

METHODS

A three dimensional computational simulation of blood flow in coronary artery symmetric stenotic model was constructed. The computational fluid dynamics (CFD) model was developed with Fluent 16.0. Blood was modeled as a shear thinning, non-Newtonian fluid with the Carreau model. A seepage outlet boundary condition and transient inlet conditions were imposed on the model. Coronary physiologica diagnostic parameter such as pressure, velocity and fractional flow reserve (FFR) were investigated in the model and compared with the microcirculation load (ML) and constant pressure load (PL) condition.

RESULTS

The present study showed the different hemodynamics in the ML and PL condition. The pre-stenotic pressure is almost the same in the two model. However the pressure in the post-stenotic artery domain is much lower in the PL model. The fluctuation range of the pressures is much higher in ML model than those in PL model. The velocity flow was more steady and lower in the ML model. For the PL model with 75% artery stenosis the FFR was 0.776, while for the ML model with the same stenosis, the FFR was 0.813.

CONCLUSIONS

This study provides evidence that FFR increased in the presentation of ML condition. There is a strong hemodynamic effect of microcirculation on coronary artery stenosis.

A hemodynamic model with a seepage condition and fluid-structure interactions for blood flow in arteries with symmetric stenosis

To strengthen the detailed understanding of arterial stenosis, we construct a novel hemodynamic model. Frequently used symmetric stenosis is employed in this work. Being different from a traditional model, this numerical model adopts microcirculation resistance as an outlet boundary condition, which is called a seepage condition. Meanwhile, fluid-structure interactions are used in the numerical simulation considering the interrelationship of blood and arterial wall. Our results indicate that (i) the region upstream of stenosis experiences very high pressures during cardiac cycles, (ii) pressure drops much faster as the flow moves into the stenotic region, and (iii) high flow velocities and high shear stresses occur in the post-stenosis region. This work provides evidence that there is a strong effect of the function of microcirculation on stenosis. This contributes to evaluating potential stenotic behavior in arteries and is pivotal in guiding disease treatment.

EFFECTS OF POROSITY IN A SEEPAGE MODEL ON HEMODYNAMICS

In this paper, we numerically investigate the effects of porosity on hemodynamics using a seepage outlet boundary condition. The results with the porosities [Formula: see text] and [Formula: see text] are compared. The comparison of the results shows that there are identical pressure, velocity and wall shear stress distributions in the artery zone; however, the velocities and wall shear stresses in the microcirculation zone with [Formula: see text] are almost as twice as those with [Formula: see text]. This work suggests that the porosity changes do not provoke variations in the artery zone, but they lead to the differences of the velocities and wall shear stresses in the microcirculation zone. The results may be the explanation of syndrome X.