טכניון מכון טכנולוגי לישראל
הטכניון מכון טכנולוגי לישראל - בית הספר ללימודי מוסמכים  
M.Sc Thesis
M.Sc StudentIshay Mark
SubjectSteady Flow in a Fully Opened Mitral Valve Shaped Orifice
DepartmentDepartment of Mechanical Engineering
Supervisors Professor Emeritus David Degani
Research Professor E Daniel Weihs
Clinical Professor Simcha Milo
Full Thesis text - in Hebrew Full thesis text - Hebrew Version


Abstract

The human heart consists of four chambers and four one-directional heart valves. Two of them have a perfectly rounded base, and two other (including mitral valve) - D-shaped bases. During an operation on diseased mitral valve, round mechanical valve is implanted into the mitral D-shaped opening. The goal of this work was to examine the possible influence of such constraint. For this purpose two numerical models were built. Each model consists of a pipe with an orifice which simulates a fully opened mitral valve for steady flow. In the first model the pipe, with a circular cross section, and the orifice are concentric and it consists of ten cases of different D-shape orifices. In the second model the pipe has a D-shape cross section and is not concentric with the orifice. This model includes three cases: the first one with D-shaped orifice at the center of the pipe; the last two - a D-shaped and a circular orifice - shifted down relative to the center of the pipe’s axis.

The concentric model results showed that there is no difference in pressure along the pipe for various orifice cross-sections and expected differences in the bubble’s size for all cases. The second model showed different bubble shapes for centered and shifted orifice cases. In addition, for both shifted orifice cases of the non-circular model, the wall shear stress is higher at the top and the side of the orifice throat in comparison to the bottom of the orifice throat. A short distance downstream of the orifice, the situation is reversed: the higher wall shear stress is at the bottom of the pipe.

For the steady flow, for the orifice simulating a fully opened heart valve, the comparison between the two models with centered orifice and the same cross section area, gave similar results. The comparison of different cases of non-circular pipe model, along with the question: "Why nature created the D-shaped orifice and why is it placed in this position?" showed advantage of the shifted circular orifice over the D-shaped one. The total power to maintain a steady flow in the pipe with a D-shaped orifice is higher by 25% than in the case of the circular one, as a result of higher values of wall shear stress and bubble length. This means that the circular orifice in the center of the pipe is preferable over the other cases.