Enhancement of Arterial Pressure Pulsatility by Controlling Continuous-Flow Left Ventricular Assist Device Flow Rate in Mock Circulatory System

Abstract

Continuous-flow left ventricular assist devices (CF-LVADs) generally operate at a constant speed, which reduces pulsatility in the arteries and may lead to complications such as functional changes in the vascular system, gastrointestinal bleeding, or both. The purpose of this study is to increase the arterial pulse pressure and pulsatility by controlling the CF-LVAD flow rate. A MicroMed DeBakey pump was used as the CF-LVAD. A model simulating the flow rate through the aortic valve was used as a reference model to drive the pump. A mock circulation containing two synchronized servomotor-operated piston pumps acting as left and right ventricles was used as a circulatory system. Proportional-integral control was used as the control method. First, the CF-LVAD was operated at a constant speed. With pulsatile-speed CF-LVAD assistance, the pump was driven such that the same mean pump output was generated. Continuous and pulsatile-speed CF-LVAD assistance provided the same mean arterial pressure and flow rate, while the index of pulsatility increased significantly for both arterial pressure and pump flow rate signals under pulsatile speed pump support. This study shows the possibility of improving the pulsatility of CF-LVAD support by regulating pump speed over a cardiac cycle without reducing the overall level of support.

Keywords: Arterial pulsatility; Continuous-flow left ventricular assist device (CF-LVAD); In vitro experiment.

Fig. 1

Mock circulation system used in experiments

Fig. 2

Schematic representation of mock circulation (top view) and block diagram of control application. Q and p are flow rate and pressure, LV and RV represent the left and right ventricles, R and C denote resistance and compliance, respectively. MV, AV, TV, and PV are mitral, aortic, tricuspid, and pulmonary valves, and ao, lv, and la are aorta, left ventricle, and left atrium, respectively. m is model, ref is reference, and e, V _in, and V _out are error and input and output voltages of DC motor driver in the control application, respectively. D is applied delay to synchronize CF-LVAD flow rate, and 1, 2, 3, and 4 denote resistances in afterload sections

Fig. 3

Experimental results for healthy (h) and DCM (dcm) conditions. a p _lv,h and p _ao,h are pressures in left ventricle and aorta, respectively, for healthy settings, b Q _av,h is flow rate through aortic valve for healthy settings, c p _lv,DCM and p _ao,DCM are pressures in left ventricle and aorta, respectively, for DCM settings, and d Q _av,DCM is flow rate through aortic valve for DCM settings

Fig. 4

a Aortic pressures (p _ao) under pulsatile- (ps) and constant-speed (cs) CF-LVAD operation modes, b pump flow rates (Q _cf-lvad) under pulsatile- (ps) and constant-speed (cs) CF-LVAD operation modes, c DC motor driver system input voltage (V _in), and d CF-LVAD operating speed (ω _{CF_LVAD})

Fig. 5

Reference CF-LVAD flow rate (Q _ref) and actual CF-LVAD flow rate (Q _CF-LVAD) (D represents applied delay synchronizing CF-LVAD flow rate)

Fig. 6

a Arterial pulse pressure, b mean aortic pressure, c index of pulsatility in aortic pressure, d amplitude of CF-LVAD flow rate, e mean pump output, and f index of pulsatility in pump flow rate under constant- (CS) and pulsatile-speed (PS) CF-LVAD support (error bars represent 2× standard deviation)