The influence of open leaflet geometry on the haemodynamic flow characteristics of polyurethane trileaflet artificial heart valves.

In vitro velocity data were obtained downstream of two versions of the Leeds polyurethane trileaflet heart valve in a simulated pulsatile flow regime using laser Doppler velocimetry. The main difference between the two valves studied was the manufacturing method used to create the valves. The film-fabricated valve was constructed from solvent-cast sheets of polyurethane, thermally formed into the correct leaflet geometry. The dip-cast valve used a stainless steel mould which was dipped into a polyurethane solution to produce the valve leaflets. Significant differences were visible between the fully open leaflet shape of each valve. The distribution of mean axial velocity and Reynolds normal stress (RNS) was shown to be dependent on the shape of the fully open valve orifice. For the film-fabricated valves, flow recirculation and high values of RNS were present downstream of the frame posts. The maximum value of RNS obtained downstream of the film-fabricated valve at peak systole was 147 N/m2. Results for the dip-cast valve showed a more uniform distribution of mean axial velocity and RNS resulting from the more circular central orifice produced by the dip-cast leaflets. The maximum value of RNS obtained downstream of the dip-cast valve at peak systole was 109 N/m2. These results demonstrate the effect of the open valve geometry on the flow characteristics downstream of trileaflet valves and that minor changes to the open leaflet geometry can significantly affect the flow characteristics and the possibility of flow-related blood damage occurring in vivo.