Continuous Flow Left Ventricular Assist Devices (CF-LVADs) generally operate at a constant speed, which causes a decrease in pulse pressure and pulsatility in the arteries. In the long run, this may lead to shape adaptation of the vascular system to better comply with the altered load. The aim of this study is to enhance the arterial pulsatility by driving the CF-LVAD at a varying speed over a cardiac cycle, such that physiological levels of time-dependent pressure change are maintained. To drive the pump at a varying speed, a feedback control mechanism was used by selecting the pump flow rate as the control variable. The varying speed pump drive mode was assessed by numerical simulations, in-vitro and ex-vivo experiments. In the simulations, a lumped parameter model was used for simulating the cardiovascular system including the heart chambers, heart valves, and systemic and pulmonary arteries and veins. A model of the Micromed DeBakey CF-LVAD was used to simulate the relation between pressure difference across the pump and flow rate. A model simulating the flow rate through the aortic valve served as reference control application. In the invitro experiments, a mock circulatory system featuring the Frank-Starling mechanism of the both left and right ventricle was used for mimicking the ventricular pressures and circulatory flows. A Micromed DeBakey CF-LVAD was used as the assisting device in this model. In the ex-vivo experiment, an isolated porcine heart was used, again with a Micromed DeBakey CF-LVAD as the assisting device. The same control mechanism as in the simulations was applied, with a reference flow rate derived from a trigonometric function. The heart was paced at 140 bpm to obtain a constant cardiac beat duration each cycle. For comparison, the CF-LVAD was also operated at a constant speed, being the mean CF-LVAD speed as applied in pulsatile mode in both simulations and experiments. The mean arterial pressure level was the same under different CF-LVAD assistance modes while the pulse pressure and pulsatility were significantly higher under varying speed pump support. Simulations and experimental results showed that it is possible to generate more pulsatile hemodynamics in arteries by operating the CF-LVAD at a varying speed over a cardiac cycle. This may avoid long-term complications such as Aortic Insufficiency (AI) and Gastro-intestinaI (GI) bleeding in CF-LVAD patients.
|Title of host publication||Medical Devices and Design in Cardiovascular Applications|
|Publication status||Published - 2013|