Elliptic varying LVAD speed over a cardiac cycle

Purpose: Continuous fl ow LVAD support reduces the pulsatility in the circulation leading to long-term complications. The purpose of this study was to obtain pulsatile and physiological systemic blood fl ow while maintaining the LVAD support, through more advanced pump control. Method: A numerical cardiovascular system model was used to simulate healthy and pathological conditions in the heart. A numerical pump model was developed by considering the static performance curves of the HeartMate II. Two different elliptic speed profi les over a cardiac cycle were applied to the LVAD. Elliptic speed variation allows smooth transitions from low to high speeds. The pump speed curve has the shape of two semi-ellipses, with a maximum at midsystole and a minimum at mid-diastole. The ratio systole/diastole may vary from beat to beat without inducing speed and/or acceleration discontinuities. Lowest and highest operating speeds were adjusted so as to obtain the same cardiac output values as achieved with constant operating speeds. Therefore, it was possible make an accurate comparison with the constant LVAD operating speed assistance. Results: To compare the constant speed and variable speed assistance pulsatility indexes (PI) were calculated for hemodynamic variables. Healthy PI values were used to normalize all PI values. PI values increased remarkably under the assistance of the varying LVAD operating speeds almost equaling normal healthy values. In full support, the aortic valve remains closed over a cardiac cycle in an LVAD supported heart. Conclusion: Pulsatility in the systemic circulation is reduced by constant speed LVAD support. It is possible to obtain more pulsatile and physiological blood fl ow by applying an elliptic speed variation to the LVAD over the cardiac cycle.