Hydrodynamic function of polyurethane prosthetic heart valves: influences of Young's modulus and leaflet thickness

The development of flexible polyurethane heart valves has been hindered by material degradation in vivo. Low modulus polyurethane leaflets are regarde d as desirable to achieve good hydrodynamic function. However, low modulus materials may suffer high strain accumulation, hence poor durability. Highe r modulus materials may improve durability, but may have poor hydrodynamic function. This study examines the hydrodynamic behaviour of biostable polyurethane va lves, varying Young's modulus from 5 to 63.6 MPa and mean leaflet thickness from 48-238 mum. Parameters studied included mean pressure gradient, energy losses and regur gitation over 5 equivalent cardiac outputs (3.6, 4,9, 6.4, 8.0 and 9.61 min (-1)). At low cardiac output, modulus was not significantly correlated with any parameter of valve opening. At 9.6 1 min(-1), modulus significantly in fluenced mean pressure gradient (p = 0.033). Mean leaflet thickness signifi cantly correlated with mean pressure gradient and energy losses during forw ard flow at all cardiac outputs (p <0.001). This study demonstrates that, over a wide range of moduli, valve hydrodynam ic function is not affected significantly by the material modulus. Leaflet thickness is a highly significant factor. Higher modulus elastomers in a ra nge up to 32.5 MPa may be useful in prosthetic heart valve leaflet manufact ure, retaining good hydrodynamic function while potentially extending the l ifetime of the valve. (C) 2001 Elsevier Science Ltd. All rights reserved.