Description
In December 2013, the American Heart Association (AHA) determined that approximately 5.1 million Americans over the age of 20 suffer from heart failure. About 3000 of these patients are in need of a heart transplant, with an approximation of only 2000 available donor hearts. Given the expectation of an increase in patients who will be diagnosed with end stage heart failure and an insufficient number of donor hearts for these patients, there is an urgency for the development of an effective artificial device. Currently, a common device which continues to gain acceptance is the Left Ventricle Assist Device (LVAD), an implantable blood pump that assists in improving the heart's cardiac output. Unfortunately during LVAD support, approximately 20% of patients develop aortic insufficiency (AI) within the first year of implantation primarily due to a reduction of the opening of the aortic valve. The aortic valve opening is critical in preventing valve fusion, AI and thrombosis formation during LVAD assistance. A speed control algorithm was developed to allow intermittent aortic valve opening without significantly reducing cardiac output. The Programmed Low Speed Algorithm (PLSA) developed by the Thoratec Corporation, and tested using a HeartMate II LVAD in the San Diego State Bioengineering, mock circulatory loop. This algorithm provides a continuous motor speed with a dwell time where the speed is decreased to a low speed. Experiments performed using the mock loop assessed the hemodynamics using two levels of cardiac support, while at the same time testing the LVAD using non-PLSA and PLSA conditions. The LVAD speeds were adjusted to test non-PLSA speeds LVADOff (LVAD conduit clamped) and 6-11 krpms, while the PLSA conditions varied high speeds of 8-11 krpms with low speeds of 6-8 krpms, with a constant dwell time of 6s. During the experimental process, left ventricle and aortic pressures were recorded along with LVAD and total aortic flows. Aortic root pulsatility, aortic valve opening duration and area, and LVAD back flow were analyzed using MATLAB software. The LVADOff conditions characterized the baseline cardiac function; and the Low setting corresponded to a cardiac output of 2.8 L/min, stroke volume of 40 ml, and ejection fraction of 22%. The Medium setting produced 3.5 L/min, 50 ml and 28%. Results indicated that the PLSA controller with a high speed of 10 krpm, and dropping to a 7 krpm low speed, was necessary to open the aortic valve for all levels of cardiac function tested. Total aortic flow acquired from the experimental procedure revealed a slight reduction (<10%) compared to non-PLSA conditions. Aortic root pulsatility significantly increased during LVAD speeds with aortic valve opening. In summary, all results from this study suggest that the developed PLSA controller generates the ability to create sufficient aortic valve opening without diminishing the heart's cardiac output and allowing for the improvement of flow mixing.
