Development of a device to impose myocardial mechanical stress for the quant itative reproduction of volume and pressure overload in vivo

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We have developed a framework to translate ventricular load into myocardial load in this study. By finite element analysis using nonlinear homogenous isotropic material and thick-walled sphere geometry, we obtained transmural stress and strain distribution. While the law Laplace does not give stress distribution, finite element analysis requires a large computational cost and was unsuited for real-time application. To circumvent these problems, we developed a new method to calculate stress distribution by applying the law of Laplace to each layer of a multi-layer myocardial model. This method enabled us to calculate stress distribution without too much computational cost, but taking nonlinear material property and finite geometric deformation into consideration. This method is, however, only applicable to spheric ventricular model with homogenous isotropic material. Analogous to finite element analysis, subendocardial stress is larger than subepicardial stress. In volume overload such as aortic regurgitation, myocardial stress became pronounced during late diastole and early ejection phase, while (in press)ure overload such as aortic stenosis, stress and strain became pronounced during ejection phase. With this method, one can calculate myocardial strain distribution in quantitative manners in real-time. We have also custom made circuitry and software to impose mechanical strain, thus calculated by computers.