STRUCTURAL-ANALYSIS OF THE BJORK-SHILEY DELRIN(R) HEART-VALVE OCCLUDER

Background and aims of the study: Impact wear grooves were evident in some Delrin(R) occluder discs of explanted Bjork-Shiley Delrin (BSD) h eart valves. This study focuses on the finite element analysis (FEA) m ethod to understand the maximum principal stresses experienced during the peak in vivo loading of valves in the closed position. Materials a nd methods: The maximum pressure difference across the valve was measu red to be 130 mmHg in a pulse duplicator simulating normal sinus rhyth m obtained clinically by cardiac catheterization. The corresponding me asured strain was 1.81 x 10(-3). The FEA model incorporated four point s of contact between the disc and the orifice ring to estimate the max imum principal stresses in the disc of the BSD heart valve. A linear p ressure distribution averaging 130 mmHg was applied so that the finite element results gave a strain of 1.81 x 10(-3) at the gauge location as experimentally observed. Results: The largest stress in the Delrin disc of the BSD valve occurred when the occluder made four-point conta ct with the orifice ring struts. The resulting localized compressive s tress on the inflow side could be as high as 42 ksi, assuming the Hert zian contact theory. The magnitude of tensile stresses were less, but were highest on the outlet surface opposite the point of contact. The highest tensile stress for an ungrooved disc was found to be 8.35 ksi, which was below the ultimate tensile strength and yield stress in fle xure for Delrin. Therefore, it is unlikely that yielding or tensile fa ilure will occur at this level of stress. Maximum tensile stresses wer e found to be 1.442 and 1.448 ksi for discs with single and multiple g rooves respectively. Conclusion: The model predicts that as a wear gro ove is created, the area of contact between the disc and the inlet str ut of the BSD valve will increase, thereby reducing average compressiv e contact stress and hence, the wear rate.