Mechanical Properties of Human Mitral Valve Chordae Tendineae: Variation with Size and Strain Rate

Abstract

A knowledge of the mechanical properties of valve tissue is a necessary prerequisite for a better understanding of valvular behavior and the design of prosthetic heart valves. Elastic response of chordae tendineae under strain rates of 0.05 cm min−1(6.25% min−1) to 12.7 cm min−1 (1600% min−1) were obtained by the application of an uniaxial tensile stress using an Instron machine. The chordae exhibited viscoelastic properties in that extensibility decreased with increasing strain rates. The approximate maximum physiological strain rate of the chordae was estimated from echocardiographic traces at the instant of valve closure, and a high value of 29 (S.D. = 9) cm s−1 (2000% s−1) was found. The breaking strain and stress were found to have values of 21.4 ± 0.5% and 3.1 ± 0.1 × 108 dyn cm−2 respectively, and were independent of strain rates (1 dyn = 10−5 N). These values are typical of collagen fibers. The final modulus, before the proportional limit, was found to be about 109 dyn cm−2, which is again typical of collagen fibers. In addition, smaller chordae exhibited less extensibility than the larger chordae. This behavior could be due to structural and functional differences and allows the more centrally inserted chordae to maintain an even valve surface during valve closure.