ESTIMATION OF LEFT-VENTRICULAR MYOCARDIAL ELASTICITY AND VISCOSITY BYA THICK-WALLED SPHERICAL MODEL

The authors measured the transfer function (TF) of the left ventricle (LV) in an isolated canine preparation. Here TF indicates the ratio of induced vibration in LV to input vibration when an external mechanica l oscillation is applied. TF had a single peak the frequency of which changed from 40 Hz to 80 Hz when LV pressure (LVP) increased from 6 mm Hg to 96 mm Hg. A mathematical model was formulated to estimate the v iscoelasticity of the spherical shell. This model was constructed of t he material points, elastic components which connected all the materia l points, and viscous components placed in series with elastic compone nts. Theoretical TF can be computed if the viscoelastic values are giv en. The value of viscoelasticity at which the theoretical TF best fitt ed the experimental TF was considered to be the viscoelasticity of the model. The validity of this approach was verified using a silicone sp herical shell. The estimated myocardial elasticity was 40 kPa when LVP was 6 mm Hg, 160-170 kPa when LVP was 96 mm Hg and was approximately proportional to LVP, whereas viscosity showed small change. The inclin ation of elasticity was consistent with previous reports. These result s proved that myocardial elasticity can be estimated by analysing the transfer function of the left ventricle.