P19: Modeling the Effects of Heartbeat Synchronized Speed Modulation for a Pediatric LVAD

Study: Increasing the pulsatility of combined LVAD and heart output can be done by modulating the speed of the pump driver in synchrony with the heart rhythm. Increased pulsatility is closer to the physiological norm, lessens blood stagnation, and improves baroreceptor feedback for pressure regulation. This study is a first step to model the systemic response to pump speed modulation to develop the precise synchronization timing and controls for an optimized outcome and to analyze the results. Methods: A previously validated computational model of a mock circulatory loop is used as a platform to observe the hemodynamic effects of synchronized pump speed modulation on the heart. A model of a brushless DC motor used to drive the pediatric LVAD is established using the speed, torque, and inertia constants of the manufacturer specification sheet to represent the motor’s ability to change speed. The pressure and flow HQ curve of the LVAD impeller is used to calculate the pump output flow at different pressures and impeller speeds. The flow of the set speed LVAD is 3L/min, and the flow of the speed modulated LVAD varies between 1 L/min and 5 L/min at diastole and systole respectively. A PID controller is used to control the pump speed to reach the desired flow output. Results: The modulated LVAD flow results in larger changes in aortic pressure. The speed modulated LVAD had an aortic pressure difference of 20 mmHg between the minimum diastole and maximum systole values while the set speed LVAD had a difference of 7 mmHg. The set speed LVAD and the speed modulated LVAD had similar average aortic pressure values of 93mmHg and 91mmHg respectively. The changes in aortic pressure at systole and diastole resulting from the speed modulated flow show that synchronized motor speed modulation results in physiologic conditions closer to the norm.Figure 1. Overview of the Mock Circulatory Loop model and LVAD motor speed controller.Figure 2. Left Ventricular and Aortic Pressure with a set speed LVAD and a speed modulated LVAD.