Fluid-solid interaction: benchmarking of an external coupling of ANSYS with CFX for cardiovascular applications

Verification of the coupled-momentum method with Womersley's Deformable Wall analytical solution

In this paper, we perform a verification study of the Coupled-Momentum Method (CMM), a 3D fluid-structure interaction (FSI) model which uses a thin linear elastic membrane and linear kinematics to describe the mechanical behavior of the vessel wall. The verification of this model is done using Womersley's deformable wall analytical solution for pulsatile flow in a semi-infinite cylindrical vessel. This solution is, under certain premises, the analytical solution of the CMM and can thus be used for model verification. For the numerical solution, we employ an impedance boundary condition to define a reflection-free outflow boundary condition and thus mimic the physics of the analytical solution, which is defined on a semi-infinite domain. We first provide a rigorous derivation of Womersley's deformable wall theory via scale analysis. We then illustrate different characteristics of the analytical solution such as space-time wave periodicity and attenuation. Finally, we present the verification tests comparing the CMM with Womersley's theory.

Anatomic and flow dynamic considerations for safe right axillary artery cannulation

OBJECTIVES

Neuroprotection is of paramount interest in cardiac surgery. Right axillary artery cannulation is well established in aortic surgery because it significantly improves survival and outcome, but malperfusion of the right brain after direct cannulation has been reported. Anatomically, 4 vessel segments are potentially amenable for cannulation of the subclavian and axillary arteries. Clinical studies vary widely in dissection sites and cannulation techniques. We investigated critical flow dynamics in the right brain caused by arterial inflow after direct cannulation and specified cannulation positions that provide optimal cerebral perfusion.

METHODS

Distances from the lateral margin of the axillary artery and the subclavian artery to the origin of the vertebral artery were measured in 14 human corpses by a flexible ruler. We calculated the hemodynamics within the vertebral artery, depending on different positions of the cannula tip, in a computer-calculated model.

RESULTS

The mean distance from the axillary artery to the vertebral artery was 8.5 cm, and the mean distance from the subclavian artery to the vertebral artery was 6.7 cm. Computed flow calculations demonstrated reversed flow in the vertebral artery when the cannula tip was positioned too close to its orifice. To ensure safe supra-aortic flow, a cannula can be inserted securely up to 6.0 cm into the axillary artery and 4.2 cm into the subclavian artery.

CONCLUSIONS

Direct cannulation of the right axillary artery can lead to cerebral malperfusion, caused by an obstruction of the vertebral artery's orifice by the arterial cannula or a subclavian steal phenomenon due to flow reversal. The safety of direct axillary artery cannulation can be improved by a well-considered dissecting site and insertion length of the cannula.

Adaptation and development of software simulation methodologies for cardiovascular engineering: present and future challenges from an end-user perspective

This paper describes the use of diverse software tools in cardiovascular applications. These tools were primarily developed in the field of engineering and the applications presented push the boundaries of the software to address events related to venous and arterial valve closure, exploration of dynamic boundary conditions or the inclusion of multi-scale boundary conditions from protein to organ levels. The future of cardiovascular research and the challenges that modellers and clinicians face from validation to clinical uptake are discussed from an end-user perspective.

Fluid—structure interaction in axially symmetric models of abdominal aortic aneurysms

Abdominal aortic aneurysm disease progression is probably influenced by tissue stresses and blood flow conditions and so accurate estimation of these will increase understanding of the disease and may lead to improved clinical practice. In this work the blood flow and tissue stresses in axially symmetric aneurysms are calculated using a complete fluid—structure interaction as a benchmark for calculating the error introduced by simpler calculations: rigid walled for the blood flow, homogeneous pressure for the tissue stress, as well as one-way-coupled interactions. The error in the peak von Mises stress in a homogeneous pressure calculation compared with a fluid—structure interaction calculation was less than 3.5 per cent for aneurysm diameters up to 7 cm. The error in the mean wall shear stress, in a rigid-walled calculation compared with a fluid—structure interaction calculation, varied from 30 per cent to 60 per cent with increasing aneurysm diameter. These results suggest that incorporation of the fluid—structure interaction is unnecessary for purely mechanical modelling, with the aim of evaluating the current rupture probability. However, for more complex biological modelling, perhaps with the aim of predicting the progress of the disease, where accurate estimation of the wall shear stress is essential, some form of fluid—structure interaction is necessary.

A three-dimensional model of fluid–structural interactions for quantifying the contractile force for cardiomyocytes on hybrid biopolymer microcantilever

Quantitatively analysis of the contractility of cardiomyocytes is important for understanding the mechanism of heart failure as well as the molecular alterations in diseased heart cells. This paper presents a realistic computational model, which considers the three-dimensional fluid-structural interactions (FSI), to quantify the contractile force of cardiomyocytes on hybrid biopolymer microcantilevers. Prior to this study, only static modeling of the microscale cellular force has been reported. This study modeled the dynamics of cardiomyocytes on microcantilevers in a medium using the FSI. This realistic model was compared with static finite element modeling (FEM) analysis and the Stoney's equation-based analytical solution, and was validated by the deflections of the microcantilevers in the experimental results. Using harmonic response analysis in FSI modeling, the motion of a hybrid biopolymer microcantilever in the medium was identified as a second-order system and the influence of the dynamics of cardiomyocytes could be evaluated quantitatively.

Finite element modelling and simulations in cardiovascular mechanics and cardiology: A bibliography 1993–2004

The paper gives a bibliographical review of the finite element modelling and simulations in cardiovascular mechanics and cardiology from the theoretical as well as practical points of views. The bibliography lists references to papers, conference proceedings and theses/dissertations that were published between 1993 and 2004. At the end of this paper, more than 890 references are given dealing with subjects as: Cardiovascular soft tissue modelling; material properties; mechanisms of cardiovascular components; blood flow; artificial components; cardiac diseases examination; surgery; and other topics.