For investigation concerning the interaction of the natural heart with various types of assist devices, a computer model was developed. The development process starts in 1992 using a specialized simulation language (AGO). Know the actual version is implemented in Matlab^â/Simulink^â. The numerical model is based on concentrated parameters and mimics the behavior of the whole circulatory system. The actual version simulates properly the dynamic pressure volume characteristics of both left and right ventricle, respectively left and right atrium, the Frank-Starling-behavior, the impedance of the proximal vessels as well as arterial and pulmonary autoregulation mechanism. It is capable to realize multidimensional parameter variations of heart rate, arterial pressure, blood volume, left ventricular contractility, right ventricular contractility as well as any degree of heart valve insufficiency in order to study hemodynamic effects and cardiac energetics based on various clinical indicators. Further it is useful to simulate parameters, which cannot be measured directly in vivo, and it is able to mimic pathologic conditions, which should be avoided in in-vivo-experiments and particularly in patients.

The system was used successfully for the development of various kinds of control algorithms and strategies, to investigation cardiac energetics in case of weaning from rotary blood pump. Previous applications of the model are the evaluation of pressure-volume loops in cases of aortic valve stenosis, determination of heart work during skeletal muscle support and, with particular refinements of the aorta and investigation of compliance mismatch effects, as they occur in aortic prostheses.

Currently the system is used to investigate the differences in hemodynamic and heart work at continuous versus pulsatile assistance. The following movies shows pulsatile PV-loops of the left ventricle in "Full to Empty" mode and "Synchronized" mode at different left ventricular contractility's and ejection delays, as well as PV-loops of the continuous assisted left ventricle at various contractilities.

The features of axial pumps allow reducing pump flow for extended times and make them, therefore, excellent candidates for patients that appear capable of ventricular recovery and weaning. However, if such pumps are adjusted to low rotational speeds   and mean flows near zero, forward-backward flow pulsations through the pump will cause considerable positive and negative instantaneous values of flow. Consistent with these observations, some currently available controllers do not allow speed to be adjusted below a set level for reasons of safety. These flow conditions are already somewhat equivalent to aortic valve insufficiency, because they require the heart to eject an additional volume during systole that is returned by backflow through the pump during diastole. Thus, a mean flow of zero is not equivalent to a unassisted patient, as it would be in a patient with a pulsatile, valved assist device, where pump stoppage causes valve closure.