Energetic parameters changes with mechanical ventilation in conjunction with BVAD assistance

BVAD is used for assistance in cases of global cardiac dysfunction and is supposed to provide an adequate peripheral perfusion. It can further help heart recovery when it is used to this aim. The study of ventricular energetics can give information on the assistance effects. Simultaneous presence of mechanical ventilation of the lungs causes some side-effects that influence ventricular energetics. Aim: To assess the influence of BVAD on ventricular energetics parameters (external work - EW, oxygen consumption - VO2, cardiac mechanical efficiency - CME) in cases when mechanical ventilation is applied. Methods: The experiments were performed using a computer simulator of cardiovascular system (CARDIOSIM(C)). It is a modular lumped parameter model where Starling's law of the heart is reproduced for both ventricles by a variable elastance model. Experiments were conducted assisting both ventricles after modelling a pathological state of the left ventricle (Emax= 0.9 mmHgocm-3) and increasing pulmonary resistance (0.3 mmHgocm-3os). To simulate the effect of mechanical ventilation, mean intrathoracic pressure (Pt) was changed from -2 to 5 mmHg. The experiments were repeated for three values of systemic arterial resistance. Results: Together with EW, VO2 and CME as a function of Pt, potential energy (PE) too is presented. PE contributes to the calculation of VO2 and is significant to evaluate the position of ventricular work cycle. Conclusions: This simulation showed that application of BVAD: ?Reduces EW and that this effect is stressed by positive Pt. ?Reduces CME that is quite insensitive to Pt. ?Increases VO2. This effect is progressively reduced by positive Pt. The increase of PE at the onset of BVAD assistance evidences a rightwards shift of ventricular work cycle (unloading of the ventricles). Positive Pt values reduce this effect. This simulation showed that, in general, positive Pt values during BVAD assistance adversely affect ventricular energetics.