Low frequency dynamic viscoelastic properties of human mitral valve tissue

The dynamic viscoelasticity of the anterior leaflet of human mitral valves was investigated by subjecting the ventricular aspect of membranous samples of the tissue to sinusoidal fluid pressures. The frequency range of the stressing function used was from 0.5 Hz to 5 Hz. The storage modulus of the tissue was found to be independent of the stressing frequency and an average value of 2.55 (SE = 0-12) X 10(8) dyn cm-2 was observed. Losses were small and the phase shift between stressing function and resulting strain and hence the loss modulus increased with frequency. For the frequency range investigated the phase shift varied from 0.04 to 0.06 rad and the loss modulus was of the order of 10(7) dyn cm-2. From the observed data it was concluded that any tissue substitute used in mitral valve replacement should be rather inextensible and have a low loss modulus. Also under normal physiological conditions, the mitral valve cannot bulge into the left atrium during peak ventricular systole and hence events in the cardiac cycle, such as the presence of the atrial pressure 'c' wave, that involve the distensibility of the valve need to be re-examined.