The monostrut strength.
The fatigue endurance limit for Haynes 25 from which the Björk-Shiley (B-S) valve is made is 4900 kg per square centimeter (70000 pounds per square inch). A welded strut may have a variation of fatigue endurance limit from 4900 kg per square centimeter (70000 pounds per square inch) in an incomplete weld with phase segregation. To avoid a weld with this variation, the monostrut has been developed, where the valve is made by electrochemical machining from one piece of Haynes 25. The homogenous outflow monostrut will then have a stable fatigue endurance limit of 4900 kg per square centimeter (70000 pounds per square inch). In a pulse duplicator at a pulse rate of 120 and a peak ventricular pressure of 200 mmHg, the maximum inservice tensile stresses for the 29 mm valve outflow strut do not exceed 700 kg per square centimeter (9800 pounds per square inch). Therefore, a seven times safety limit is present for the monostrut under maximal physiological stress conditions. The struts in the B-S monostrut valve cannot be fractured even under extreme experimental conditions and never under peak physiological conditions.
D004867:Equipment Design / Q000592:standards*; D004869:Equipment Safety; D006350:Heart Valve Prosthesis / Q000592:standards*; D006801:Humans