Accuracy vs. computational time: translating aortic simulations to the clinic.

It has long been recognized that the forces and stresses produced by the blood flow on the walls of the cardiovascular system are central to the development of different cardiovascular diseases (CVDs). However, up to now, the reason why arterial diseases occur at preferential sites is still not fully understood. This paper reviews the progress, made largely within the last decade, towards the use of 3D computational fluid dynamics (CFD) models to simulate the blood flow dynamics and its interaction with the arterial wall within the human thoracic aorta (TA). We describe the technical aspects of model building, review methods to create anatomic and physiologic models, obtain material properties, assign boundary conditions, solve the equations governing blood flow, and describe the assumptions used in running the simulations. Detailed comparative information is provided in tabular format about the model setup, simulation results, and a summary of the major insights and contributions of each TA article reviewed. Several syntheses are given that summarize the research carried out by influential research groups, review important findings, discuss the methods employed, limitations, and opportunities for further research. We hope that this review will stimulate computational research that will contribute to the continued improvement of cardiovascular health through a strong interaction and cooperation between engineers and clinicians.

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A Review on Computational Fluid Dynamics Modelling in Human Thoracic Aorta

Analysis of the effects of different pulsatile inlet profiles on the hemodynamical properties of blood flow in patient specific carotid artery with stenosis

Pulsatile extracorporeal circulation during on-pump cardiac surgery enhances aortic wall shear stress.

The development of an engineering transitional turbulence model and its subsequent evaluation and validation for some diseased cardiovascular flows have been suggestive of its likely utility in normal aortas. The existence of experimental data from human aortas, acquired in the early 1970s with catheter-mounted hot film velocimeters, provided the opportunity to compare the performance of the model on such flows. A generic human aorta, derived from magnetic resonance anatomical and velocity images of a young volunteer, was used as the basis for varying both Reynolds number (Re) and Womersley parameter (α) to match four experimental data points from human ascending aortas, comprising two with disturbed flow and two with apparently undisturbed flow. Trials were made with three different levels of inflow turbulence intensity (Tu) to find if a single level could represent the four different cases with 4000 < Re < 10,000 and 17 < α < 26. A necessary boundary condition includes the inflow "turbulence" level, and convincing results were obtained for all four cases with inflow Tu = 1.0%, providing additional confidence in the application of the transitional model in flows in larger arteries. The Reynolds-averaged Navier-Stokes (RANS)-based shear stress transport (SST) transitional model is capable of capturing the correct flow state in the human aorta when low inflow turbulence intensity (1.0%) is specified.

A numerical study of aortic flow stability and comparison with in vivo flow measurements

Simulation of blood flow in human aorta with emphasis on outlet boundary conditions

Extracorporeal circulation is a standard technique in cardiac surgery. Nevertheless, many different variations have been developed. Using computational fluid dynamics the impact of a particular perfusion technique can be simulated preoperatively. The aim of our study was to examine changes of the blood flow characteristics when perfusing the aorta with different techniques. At first we created a numerical model of a human aorta and its outlets. Then we performed simulations of antegrade pulsatile and non-pulsatile blood flow and simulated antegrade and retrograde perfusion via extracorporeal circulation canulas. At perfusion originating from canulas the flow became turbulent and its speed regionally increased up to 3,54 m/s. Otherwise perfusing retrogradely only marginal blood flow remained in the ascending aorta. Canula stream caused up to ten-fold higher local wall shear stress values, especially in the vessel roots next to the canulas and in the proximate aortic wall. Under these conditions mobilization of arteriosclerotic plaques has to be considered. Our study shows that antegrade and retrograde perfusion via canulas change important blood flow characteristics as flow speed, turbulent stream and wall shear stress.

D. Schubert

Papers

Simulation of blood flow in human aorta with emphasis on outlet boundary conditions

Aortic blood flow characteristics of different extracorporeal circulation techniques during cardiac surgery - a computational fluid dynamics study