Numerical Methods for Design and Evaluation of Prosthetic Heart Valves

Abstract

The need for mechanical analyses in heart valve prosthesis development was recognized in the mid-1900s as Dr. Hufnagel began the development and introduction of prosthetic heart valves [1]. It was recognized that the “ball valve” designs diverted the blood flow from a central flow to a flow around the balls. This can cause damage to the blood cells and also may cause the heart to work harder [2]. Tilting disc prosthetic heart valves helped restore the desirable central flow, reducing the damage to blood cells. However one design (the Bjork-Shiley valve) developed a reliability issue which resulted in multiple fatal events; this reliability issue was related to the weld used for the struts, and the valve was removed from the market by 1986. Later some structural finite element analyses were completed in attempts to quantify the stresses related to the failures and to develop differing methods of failure detection [3, 4]. The methods for failure detection involved acoustic and harmonic analyses. Experimentally, the resonant frequencies for intact and fractured struts were measured and were found to be significantly different. A finite element modal analysis of the Bjork-Shiley valve was created [5] and the responses compared favorably to the experimental studies [6, 7]. Chondros (2010) improved on these acoustic methods, and suggested a method of monitoring fatigue crack propagation in the valve strut [7]. Well-validated methods like this would be useful in identification of broken valve struts prior to any clinical symptoms.

Appendix I: Documentation Report Template

• 1.0 Introduction/Background

• 2.0 Project Objective

  (Describe the objectives of the project. For example: “The goal of this project is to determine the structural integrity of the heart valve prosthesis.” Include a description of how analysis will be used to address this project objective.)

• 3.0 Methods

  • 3.1 Approach used to address the project objectives

    (Describe how analysis and/or experiments will be used. Also describe the type of analysis being used (i.e., thermal, nonlinear structural, etc.))

  • 3.2 Significant Assumptions

    (Describe significant assumptions used in the analysis. For example: use of symmetry)

  • 3.3 Analytical Methods (Model Specifications)

    Hardware and software used:

    (Describe the system used to assemble and solve the computer model, i.e., computers, computer code, and versions.)

    Material properties:

    (List material properties used in the model. Also reference where these properties are documented.)

    Geometry:

    (Describe the geometry being used. Also reference where the geometries are documented, including part numbers if available.)

    Boundary conditions:

    (List the boundary conditions applied. Reference where these conditions are documented if appropriate.)

    Model verification: In the context of numerical simulation, the intended meaning of the term “verification” is as follows: Demonstration that a computer model is correct (mathematically) and performs as intended [50].

    (List the steps taken to ensure the model is mathematically accurate. For example: Check the mesh density to show the model is stable and has sufficient accuracy. Check the element types used to show they are appropriate for the analysis.)

    Model validation: In the context of numerical simulation, the intended meaning of the term “validation” is as follows: Demonstration that a computer model has accuracy which is satisfactory with respect to the intended use of the model, and within the intended range of application [50].

    Model objectives (What is the intended use of the model?):

    (Essentially answer this question. For example: “the model is intended to calculate stress in the screw” or “the model is intended to calculate the final temperature in the material.”)

    Model accuracy goal (What model output accuracy is satisfactory?):

    (Essentially answer this question. For example: “the model should calculate strain within 10 % of strain determined from experimental measurements” or “the model should calculate temperature to within 5 % of that measured using experiments.”)

    Test the model validation:

    (Discuss whether the model has enough accuracy as specified above. Highlight any model limitations.)

  • 3.4 Experimental Methods

    (Describe experimental testing done to support this project. Document where experimental data are stored. Document the experimental reports if not included in this report.)

• 4.0 Results

  (Describe and list the results of the simulation model as it relates to the project objective. Describe and list the results of the experimental tests as they relate to the project objective. List where these numerical and experimental results are documented.)

• 5.0 Conclusions

  (Make conclusions from the results listed above to address the project objectives.)

• 6.0 Recommendations

  (If appropriate make recommendations, such as specific types of testing, alternate directions to investigate a design, etc.)

• 7.0 References

  (Knepell PL, Arangno DC. Simulation Validation A Confidence Assessment Methodology. IEEE Computer Society Press 10662 Los Vaqueros Circle, PO Box 3014 Los Alamitos, CA 90720-1264, 1993. Add any additional references used.)

• 8.0 Appendices

  (Any other supporting documentation.)