A hybrid (numerical-physical) model of the left ventricle

Hydraulic models of the circulation are used to test mechanical devices and for training and research purposes; when compared to numerical models, how ever, they are not flexible enough and rather expensive. The solution propo sed here is to merge the characteristics and the flexibility of numerical m odels with the functions of physical models. The result is a hybrid model w ith numerical and physical sections connected by an electro-hydraulic inter face - which is to some extent the main problem since the numerical model c an be easily changed or modified. The concept of hybrid model is applied to the representation of ventricular function by a variable elastance numerical model. This prototype is an ope n loop circuit and the physical section is built out of a reservoir (atrium ) and a modified windkessel (arterial tree). The corresponding equations ar e solved numerically using the variables (atrial and arterial pressures) co ming from the physical circuit. Ventricular output flow is the computed var iable and is sent to a servo amplifier connected to a DC motor-gear pump sy stem. The gear pump, behaving roughly as a flow source, is the interface to the physical circuit. Results obtained under different hemodynamic conditi ons demonstrate the behaviour of the ventricular model on the pressure-volu me plane and the time course of output flow and arterial pressure.