Although continuous flow (CF) and pulsatile flow (PF) ventricular assist devices (VADs) are being clinically used, their effects on aortic blood flow, as a measure of overall blood distribution, remain unclear. In acute VAD support animal experiments, our group has described a zone of turbulent mixing in the aortic arch. The objective of this study was to confirm this finding in the controlled setting of an adult mock circulation, simulating ventricular pathophysiologic states (normal and failing ventricle). CF and PF flow VADs were connected to ventricular apical inflow and ascending aorta (AA) or descending aorta (DA) outflow cannulae. Cardiovascular pressure and flow waveforms were recorded at varying levels of VAD bypass resulting in four test conditions: (i) CF-AA; (ii) CF-DA; (iii) PF-AA; and (iv) PF-DA. Confirming the animal data, no differences in mean aortic flow between CF and PF VADs were found, and significantly lower mean aortic arch flow with DA cannulation was noted. Mean aortic root flow decreased with increasing VAD bypass flow. As in the animal studies, despite similar mean flow rates, significant differences in waveform morphology were observed for AA and DA outflow graft locations and varying levels of VAD bypass. At 100% VAD support in the failing heart, PF restored waveform pulsatility to normal baseline while CF resulted in little pulsatility. These results confirm our earlier findings in the animal model, suggesting that outflow graft location may have a significant effect on aortic blood flow distribution. The long-term implications of these findings are being examined in ongoing studies.

Ventricular assist devices (VADs) have been used successfully as a bridge to transplant in heart failure patients by unloading ventricular volume and restoring the circulation. An artificial vasculature device (AVD) is being developed that may better facilitate myocardial recovery than VAD by controlling the afterload experienced by the native heart and controlling the pulsatile energy entering into the arterial system from the device, potentially reconditioning the arterial system properties. The AVD is a valveless, 80 ml blood chamber with a servo-controlled pusher plate connected to the ascending aorta by a vascular graft. Control algorithms for the AVD were developed to maintain any user-defined systemic input impedance (IM) including resistance, elastance, and inertial components. Computer simulation and mock circulation models of the cardiovascular system were used to test the efficacy of two control strategies for the AVD: 1) average impedance position control (AIPC)-to maintain an average value of resistance during left ventricular (LV) systole and 2) instantaneous impedance force feedback (IIFF) and position control (IIPC)-to maintain a desired value or profile of resistance and compliance. Computer simulations and mock loop tests were performed to predict resulting cardiovascular pressures, volumes, flows, and the resistance and compliance experienced by the native LV during ejection for simulated normal, failing, and recovering LV. These results indicate that the LV volume and pressure decreased, and the LV stroke volume increased with decreasing IM, resulting in an increased ejection fraction. Although the AIPC algorithm is more stable and can tolerate higher levels of sensor errors and noise, the IIFF and IIPC control algorithms are better suited to maintain any instantaneous IM or an IM profile. The developed AVD impedance control algorithms may be implemented with current VADs to promote myocardial recovery and facilitate weaning.

Ventricular assist devices (VADs) have been used successfully as a bridge to transplant in heart failure patients by unloading ventricular volume and restoring the circulation. An artificial vasculature device (AVD) that may better facilitate myocardial recovery than VAD by controlling the afterload seen by the ejecting heart is being developed. The AVD concept is to enable any user-defined input impedance (IM) with resistance (R) and compliance (C) components. In this study, a pulse duplicator was used to test the efficacy of the AVD concept for two control strategies in an adult mock circulation: (1) R-C in series and (2) 2-element Windkessel (R-C in parallel) using instantaneous impedance position control (IIPC) to maintain a desired value or profile of R and C. In vitro experiments were performed and the resulting cardiovascular pressures, volumes, flows, and the afterload (R and C) seen by the LV during ejection for simulated cardiac failure were recorded and analyzed. Our results indicate that setting the AVD to lower IM reduced LV volume and pressure, restored LV stroke volume, and increased coronary flow. The IIPC control algorithms are better suited to maintain any instantaneous IM or an IM profile, but are susceptible to measurement noise.