In vitro strain measurement of a mechanical heart valve in a pulse simulator

To ascertain the stress magnitude at the stress concentration areas, in vitro strain measurements on a St. Vincent's mechanical heart valve were carried out in a pulse simulator. Results were combined with a finite element (FEM) stress analysis of the titanium valve housing. The maximum stress at the site of stress concentration of the titanium valve housing was 51 MPa. This is well below the fatigue endurance limit of titanium. The imposed stress on the occluder by the upper strut was less than 2 MPa. This is below the lower stress limit of Delrin and may explain why no fracture of the Delrin disk occluder has been reported. The combined use of microstrain analysis and FEM proved to be essential in the determination of dynamic stresses during the opening and closing of the mechanical heart valve.