The IABP model, inserted in the arterial tree, is considered as a source flow QIABP(t) in the following way: during the diastole the balloon inflates and the flow is positive, during the next systole the balloon deflates and the flow is negative. The flow source QIABP(t) may be replaced by a pneumatic pressure source P(t), representing the compressed gas reservoir, and by resistance (R) representing the total gas delivery resistance of the system. The pneumatic source P(t) has been modelled by describing separately the ejection and the filling phase as the air outflow from high-pressure tank, connected to the pressure source, and the air outflow from a lower-pressure tank connected to the vacuum source.
The open loop network consists of: atrial reservoir (preload), left ventricle and systemic arterial tree composed of aortic, thoracic and abdominal tracts. RAT, CAT and LAT are the resistance, compliance and inertance describing the behavior of the aortic tract. RTT (RABT), CAT (CABT) and LAT (LABT) are the resistance, compliance and inertance describing the behavior of the thoracic (abdominal) tract. LAP is the left atrial pressure, LVP is the left ventricular pressure. MV is the mitral valve and AV is the aortic valve. MV and AV are modelled using resistances and diodes. Ras is the systemic arterial peripheral (variable) resistance. Qli (Qlo) is the input (output) ventricular flow. In the electric analogue the behavior of the heart was implemented using the equations reported in the Numerical Heart Model (1) section.