Evaluation of Fluid Mechanics and Cavitation Generated by Mechanical Heart Valves During the Closing Phase

Open Access
Author:
Herbertson, Luke Herschel
Graduate Program:
Bioengineering
Degree:
Doctor of Philosophy
Document Type:
Dissertation
Date of Defense:
January 05, 2009
Committee Members:
  • Keefe B Manning, Dissertation Advisor
  • Keefe B Manning, Committee Chair
  • Steven Deutsch, Committee Member
  • Arnold Anthony Fontaine, Committee Member
  • Donna Hope Korzick, Committee Member
  • Herbert Herling Lipowsky, Committee Member
Keywords:
  • mechanical heart valve
  • cavitation
  • hemodynamics
  • laser Doppler velocimetry
  • cardiovascular
  • fluid mechanics
Abstract:
Significant advances have been made in the field of heart valve replacement, especially in terms of anticoagulation therapy and valve design. However, heart valve patients remain susceptible to complications such as hemolysis and thrombosis. For this thesis work, the closing dynamics of mechanical heart valves have been evaluated to better understand the roles of valve design and environmental conditions on the local fluid mechanics. Optical flow diagnostic tools, such as laser Doppler velocimetry, were applied to investigate near valve fluid structures suspected of causing blood damage. Modifications were made to the valve housing to enable visual access to previously inaccessible regions of flow. Specifically, the near-valve flow fields generated by the Bjork-Shiley Monostrut, St. Jude Medical, and On-X mechanical heart valves were studied. The three-dimensional flow patterns presented here reveal regions of turbulence, flow stagnation, vorticity, and flow separation near the leaflet tip. These flow conditions, in combination with cavitation, are the primary factors contributing to blood trauma induced during valve closure. Mechanisms for blood damage were further investigated by analyzing high frequency pressure fluctuations, which represent cavitation intensity. Mitral valve closing sounds contain characteristics that, when appropriately isolated, can help to diagnose cavitation, asynchronous leaflet closure, and valve impact forces. The effect of ventricular pressure, valve size, valve composition, leaflet geometry, and fluid properties on cavitation were evaluated through this work. The risk of blood damage in patients with mechanical heart valves was minimized when valve impact and rebound were dampened. Potential improvements to implantation techniques and valve design may evolve from these results.