Boundary Conditions in Simulation of Stenosed Coronary Arteries

Abstract

A powerful alternative means to studying hemodynamics in diseased or healthy coronary arteries can be achieved by providing a numerical model in which blood flow can be virtually simulated, for instance, using the computational fluid dynamics (CFD) method. In fact, it is well documented that CFD allows reliable physiological blood flow simulation and measurements of flow parameters. A requisite for obtaining reliable results from coronary CFD is to use exact anatomical models and realistic boundary conditions. To date, in almost all of the modeling studies on hemodynamics of stenosed coronary arteries, a velocity based boundary conditions has been assigned. The objective of this study is to show that inlet velocity actually depends on the degree of stenosis and thus for severe constriction in coronary artery, a velocity based boundary conditions cannot be realistic. We then prove that regardless of severity of stenosis in coronary arteries, the upstream pressure, systemic pressure, is always constant, thus, should be used as boundary conditions instead. The two sets of boundary conditions are implemented to demonstrate the robustness of each in modeling of stenosed coronary artery in a CFD study. These boundary conditions are applied in a stenosed cylindrical pipe including three categories of symmetrical stenosis (mild, moderate and severe stenosis starting from 15 to 95% diameter reduction) for steady state and pulsatile flow. Results strongly indicate that inlet velocity boundary conditions are no longer valid when effective diameter in stenosis goes below approximately 2.8 mm (a healthy diameter is considered 3.2 mm) which corresponds to 10-15% diameter reduction. Further work will determine the effect of flow reduction on the oxygen tension in blood to better define conditions for clinical symptoms such as angina.

Prosthetic Aortic Heart Valves

“…The arterial branch is then connected to the sinoatrial node and the obtuse marginal branch covers the posterior left ventricular wall towards the apex. It should be noted that veins usually follow the same pattern as the distribution of the distal arteries [22].…”

“…First, blood is pumped through the tricuspid and mitral valves as the atria contract. Following the ventricle contraction, blood is pushed backward, flowing between the flaps and walls of the ventricles [20][21][22][23]. The flaps are consequently pushed upward sothat the valvesare closed completely.…”

“…The closing phase of the heart valves is associated with an audible sound, known as the heartbeat. The first sound is because of the closure of the mitral and tricuspid valves, and the second one is when the pulmonary and aortic valves close [18][19][20][21][22].…”

“…The mechanism by which valves open and close during the cardiac cycle is known to be almost passive as the pressure gradient before and after the valves is the driving force. This pressure gradient is generated within the heart and highly depends on the compliance of the heart and arteries [10][11][12][13][14][15][16][17][18][19][20][21][22][23][24][25]. However,in the mitral valve, the opening and closing phases are not completely passive as the papillary muscles and the chordae tendineaelocated within the left ventricle partly contribute, as mentioned before.…”

Application Of Numerical Modeling In Quantitative Assessment Of BHT Dispersion In PE-HD Pipes

“…CFD is now being used with great success in many areas of science and technology, including the modeling of hydraulic parameters in water supply systems, as well as in the sewer systems [35][36][37][38][39]. One of the most popular commercial CFD software with wide range of computing capabilities is Fluent, Ansys Inc. [40][41][42][43][44]. Fluent is a comprehensive tool for the numerical analyses of single-and multi-phase phenomena in connection with heat and mass exchange, as well as with chemical reactions.…”