In vitro fluid dynamic characteristics of aortic bioprostheses: old versus new.

The in vitro fluid dynamic characteristics of a variety of old- and new-generation porcine and pericardial aortic bioprostheses were investigated under pulsatile flow conditions. The pressure drop results indicate that the old valve designs have performance indices in the range of 0.30 to 0.42, while the new, low-pressure fixed designs have performance indices of 0.50 to 0.70. Leaflet photography indicated that the new designs also have superior opening and closing characteristics. Flow visualization, and velocity and turbulent shear stress measurements, conducted with a two-dimensional laser Doppler anemometer system, indicated that all the tissue valve designs create jet-type flow fields. The intensity of the jets and turbulence levels were less severe with the new designs. The old designs created turbulent shear stresses of as little as 1500 dynes/cm2, while the new designs created turbulent shear stresses of as little as 750 dynes/cm2.