Continuous-flow pump model study: The effect on pump performance of pump characteristics and cardiovascular conditions

This model study evaluates the effect of pump characteristics and cardiovascular data on hemodynamics in atrio-aortic VAD assistance. The model includes a computational circulatory sub-model and an electrical sub-model representing two rotary blood pumps through their pressure-flow characteristics. The first is close to a pressure generator - PG (average flow sensitivity to pressure variations, -0.047 l mmHg^-1); the second is closer to a flow generator - FG (average flow sensitivity to pressure variations, -0.0097 l mmHg^-1). Interaction with VAD was achieved by means of two interfaces, behaving as impedance transformers. The model was verified by use of literature data and VAD onset conditions were used as a control for the experiments. Tests compared the two pumps, at constant pump speed, in different ventricular and circulatory conditions: maximum ventricular elastance (0.44-0.9 mmHg cm^-3), systemic peripheral resistance (781-1200 g cm ^-4 s^-1), ventricular diastolic compliance C _p (5-10-50 cm³ mmHg^-1), systemic arterial compliance (0.9-1.8 cm³ mmHg^-1). Analyzed variables were: arterial and venous pressures, flows, ventricular volume, external work, and surplus hemodynamic energy (SHE). The PG pump generated the highest SHE under almost all conditions, in particular for higher C _p (+50 %). PG pump flow is also the most sensitive to E _max and C _p changes (-26 and -33 %, respectively). The FG pump generally guarantees higher external work reduction (54 %) and flow less dependent on circulatory and ventricular conditions. The results are evidence of the importance of pump speed regulation with changing ventricular conditions. The computational sub-model will be part of a hydro-numerical model, including autonomic controls, designed to test different VADs.