A model study of isovolumic and non-isovolumic left ventricular contractions

A model of the left ventricle is proposed. It consists of a thick-walled cylinder-like cavity, the wall of which contains muscle fibres. Orientation and length of the fibres are functions of their position in the wall. During changes of preload and during ejection the dimensions of the cylinder change in a prescribed way. A sliding filament model in series with a real or apparent elastic element is applied to simulate wall tension from which the pressure in the ventricle results. To test the model and to fit the relevant parameters, experiments on isolated perfused rabbit hearts were carried out. The model could simulate isovolumic and non-isovolumic contractions reasonably well in the case when a series elasticity allowing about 6% fibre shortening was present and a preload dependent activation function was applied. Finally it must be concluded that for an accurate estimation of the parameters, not only pressure development and flow must be recorded, but also certain overall ventricular dimensions