INCREASED REGIONAL SYSTOLIC MYOCARDIAL STIFFNESS OF THE LEFT-VENTRICLE DURING CORONARY-ARTERY OCCLUSION IN A DOG - ANALYSIS OF THE FINITE-ELEMENT MODEL

(1) We measured the instantaneous systolic transfer function of an iso lated canine left ventricle (LV) before and after the ligation of the left anterior descending coronary artery (LAD). The instantaneous tran sfer function before the ligation of the LAD showed a resonance curve whose peak frequency was 30 to 70 Hz. On the other hand, the transfer function 40 min after the ligation of the LAD showed a divided peak in the resonance curve. (2) We constructed a finite element model of a t hick-walled spherical shell with a non-uniform structure. In this mode l, the myocardial elasticity and viscosity of the ischemic region are different from those of nonischemic regions. One can calculate the the oretical transfer function using modal analysis and also estimate the elasticity and the viscous coefficient of both nonischemic and ischemi c myocardium by fitting the theoretical transfer function to the exper imental one. (3) The estimated elasticity of the ischemic myocardium w as three to five times larger than that of the non-ischemic myocardium . The estimated viscous coefficient of the ischemic myocardium was abo ut half that of the non-ischemic myocardium. These results showed that ischemia alters the viscoelastic properties of the myocardium during systole as well as during diastole.