Comparative in-vitro fluid dynamics characterization of heart valve bioprostheses under accelerated fatigue conditions and under physiologic conditions

An accelerated fatigue testing system and a pulse duplicator (heart simulator) were used to evaluate the fluid dynamics characteristics of 12 cardiac bioprostheses. Pressure differences and pulsatile flow rates across the valves, as well as machine rates, were measured using a real-time on-line data-acquisition system. All other valve hydrodynamic parameters were internally calculated. For the same pressure difference, the pulsatile flow rate was higher at higher pulse rates. Regurgitation fraction values were higher for valves tested at higher speeds. Closing volumes, however, remained fairly constant. Mean transvalvular pressure difference (delta p) and root mean square pulsatile flow rate (QRMS) under accelerated testing conditions were related according to the particular case of a parabolic regression through the origin of the form (type 1), delta p = Co Q2RMS. Prosthetic valves tested in the fatigue tester presented in general a more effective area for flow than did valves tested in the pulse duplicator. Calculated discharge coefficients and performance indexes were accordingly higher. In both testing devices pericardial valves had higher effective orifice areas, discharge coefficients, and performance indexes than did porcine xenografts, and large valves performed more efficiently than small valves. Differences among regression coefficients for the same valves tested in both machines appeared to be significant in 100% of the cases. There were differences in the degrees of stenosis among valves tested in the pulse duplicator and in the fatigue tester. Understanding of fluid dynamics data obtained for undamaged valves at accelerated speeds and their relation to data obtained at physiologic speeds permitted the detection and quantification of rupture and malfunctioning of these valves without removing them from the fatigue tester.