Durability of a cardiac valve leaflet made of calf pericardium: fatigue and energy consumption.

We studied the mechanical behavior of membranes of calf pericardium, similar to those employed in prosthetic valve leaflets, when subjected to tensile fatigue. The objective was to assess its durability, as a fundamental property of cardiac bioprosthesis, and analyze the energy consumption. For this purpose, the authors built a hydraulic simulator to subject a spherical valve leaflet made of calf pericardium to cyclic stress mimicking cardiac function. A total of 522 assays were performed in 40 samples, subjected to cyclic pressures greater than 6 atm, and 482 subjected to pressures ranging between 2 and 6 atm. The mathematical expression that establishes the relationship between the pressure exerted and the frequency was obtained. If we assume that the function is continuous, this equation provides the range of fatigue tolerated for a given number of cycles. Using the optimal values (the five highest values per series), the expression was found to be y = 9.95x(-0 1214) (R(2) = 0.955), where x represents the frequency in cycles per second and y the pressure in atmospheres. In addition, we established the mathematical relationship between the energy consumed and the frequency, which was a function of the pressure exerted, regardless of the region or zone from which the samples had been obtained. The methods of manual and morphology-based selection employed produced widely dispersed results. When a mechanical criterion was included, the similarity in the energy consumed during fatigue testing markedly improved the correlation, with a coefficient of determination between paired samples of R(2) = 0.7477. A mechanical criterion, such as energy consumption, can help to improve sample selection and produce more consistent results. Finally, we obtained the mathematical expression that relates the energy consumed to the pressure exerted and the number of cycles per second to which the valve leaflet was subjected. This procedure enables us to establish the limit to the energy that a biomaterial can consume over a period of time during which it is subjected to a working pressure and, thus, calculate more precisely its durability.