The use of porcine or bovine pericardium biological cardiac valves has as its main disadvantage a relatively short lifespan, with failures due to calcification and fatigue. Increasing these valves' durability constitutes a great challenge. An understudied phenomenon is the effect of flutter, an oscillation of the leaflets that can cause regurgitation and accelerate calcification and fatigue. As a starting point to study how to reduce or prevent these oscillations, a method was developed to quantify the flutter frequencies occurring at the point of the valve's full opening. On a test bench that simulates the heart flow, the cusp behaviors of eight biological valves were filmed with a high speed camera at 2000 frames per second at different flow rates and motion capture software obtained the frequencies and amplitudes of the vibrations of each leaflet. Oscillations in the range of 200 Hz with average amplitudes of 0.4 mm were found; larger nominal diameter valves obtained lower values, and bovine pericardial valves had superior performance compared to porcine valves. A dimensionless analysis was performed to find a relationship between the geometric and mechanical properties of the valves with the critical speed of the onset of fluttering. This relationship inspired a method to predict whether flutter will occur in the bioprosthesis. This method is a new tool for the consideration of maximizing the life of prosthetic valves.
Biological prosthetic valves are known for having good hemodynamics and resistance to clot formation, but they also have the disadvantage of possessing a short lifespan. An understudied effect is the fluttering of cusps, which is associated with calcification, hemolysis, and fatigue. The present study used a mathematical model of eigenvalues calculation to predict the critical speed of flutter onset in porcine and bovine pericardium valves, comparing the results with experiments on a test bench. Most results were below the speeds found experimentally, an outcome usually found in other flutter analytical theories. The analytical method demonstrated that pericardial valves have greater resistance to the onset of flutter than porcine valves, which agrees with experimental results. The sensitivity analysis showed that the internal diameter has a high impact on the critical speed, while thickness has greater importance when considering critical flow. The same analysis demonstrated that the higher thickness and elastic modulus values of pericardial valves explain why it has an increased resistance to cusps oscillation in comparison with porcine. The mathematical model in this paper is the first flutter analytical theory focused on heart valves. It can assist in new bioprosthesis projects that can be more resistant to oscillations and early fatigue failure.
The use of biological prosthetic valves has increased considerably in recent decades since they have several advantages over mechanical ones, but they still possess the great disadvantage of having a relatively short lifetime. An understudied phenomenon is the flutter effect that causes oscillations in the cusps, which is associated with regurgitation, calcification and fatigue, which can reduce even more the lifetime of bioproteses. In an experimental bench that simulates the cardiac flow, the behavior of a porcine and a bovine pericardium valves was recorded by a high-speed camera to quantify the oscillations of the cusps and an experiment using particle image velocimetry was conducted to study the velocity profiles and shear stresses and their relations with flutter. Results showed that the pericardial valve has lower values of frequencies and amplitudes compared to the porcine valve. Lower velocity values were found in the cusps that did not have flutter, but no relationship was observed between shear stress values and leaflet vibrations. These results may assist in future projects of biological prosthetic valves that have less flutter and longer lifespan.
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