Estimation of left ventricular myocardial elasticity and viscosity by a 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 mechanical 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 viscoelasticity of the spherical shell. This model was constructed of the material points, elastic components which connected all the material points, and viscous components placed in series with elastic components. Theoretical TF can be computed if the viscoelastic values are given. The value of viscoelasticity at which the theoretical TF best fitted the experimental TF was considered to be the viscoelasticity of the model. The validity of this approach was verified using a silicone spherical 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 inclination of elasticity was consistent with previous reports. These results proved that myocardial elasticity can be estimated by analysing the transfer function of the left ventricle.