Design and control of the atrio-aortic left ventricular assist device based on O2 consumption.

The left ventricular assist device (LVAD) is used in parallel with the left ventricle to temporarily assist patients with diminished cardiac function for the purpose of minimizing heart workload and to maintain systemic arterial perfusion. The proper adjustment and timing of the pneumatic LVAD is important such that this goal is achieved. Previous investigations into the left ventricular assist device are inconclusive regarding the optimal utilization of this device. This paper documents a protocol for optimal timing of the LVAD. Timing is studied using a closed-loop analog model of the heart, vascular system, and the LVAD. The model is tested for basic representation of the physiological system. The LVAD is incorporated into the model to discover its interaction with cardiac preload and afterload. Heart workload is computed via the pressure-volume-area method. The normal and impaired heart are modeled, in each case the pump control variables are adjusted. A protocol for adjustment of the LVAD is proposed based on reduced heart oxygen consumption. It was found that the pump should begin ejection immediately after the close of the aortic valve and that the pump filling pressure should be set to a value which produces maximum filling of the pump. Although aortic pressure and flow could be improved at pump rates above the heart rate, oxygen utilization of the heart could only be minimized for synchronous pumping. The adjustment of the pump ejection pressure is a tradeoff between d/dt (LVO2) and stroke volume and mean arterial pressure. The LVAD should be designed to minimize inflow and outflow resistance and to maximize pump compliance. The process of weaning the patient from the LVAD is considered. The overall results provide quantitative guidance for the use of the AA-LVAD.