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© 2012, Copyright the Authors Artificial Organs © 2012, International Center for Artificial Organs and Transplantation and Wiley Periodicals, Inc.

Physiological Controller of an Intra-Aorta Pump Based on Baroreflex Sensitivity
Bin Gao, Yu Chang, Kaiyun Gu, Yi Zeng, and Youjun Liu
School of Life Science and BioEngineering, Beijing University of Technology, Beijing, ChinaAbstract: Left ventricular assist devices are increasingly used for long-term support in heart failure patients. It is important to find an optimum operating point for the pump that is appropriate for the existing function of the heart and the state of the circulatory system. Therefore, baroreflex sensitivity (BRS), as an indicator of heart function, is chosen as the control variable. In order to find anoptimum point automatically, an extremum search algorithm (ESA) is designed to find an optimal mean arterial pressure (MAP), for which the BRS is maximum. Then, a MAP controller based on model-free adaptive control is designed to ensure that the measured MAP tracks the desired one. In order to test the feasibility of the control strategy, numerical simulations and simplified in vitro experimentswere conducted. A mathematic model of the

cardiovascular system simulating left ventricular failure, physical activity, and recovery of cardiac function is used in the simulation. The numerical simulations show that the maximum value of BRS can be found automatically by using ESA. The rotational speed of the pump is automatically increased (from 6500 rpm to 7000 rpm), and peripheral resistance isdecreased to simulate slight physical activity. When Emax is increased from 0.6 mm Hg/mL to 1.8 mm Hg/mL to mimic heart recovery, the speed is decreased from 7000 rpm to 6300 rpm in response. The optimum operating point for the pump can be detected by the proposed control strategy without the need to set a reference value for the control variable by operators. Key Words: Baroreflexsensitivity—Heart recovery—Modelfree adaptive control—Intra-aortic pump.

Although rotary blood pumps (RBPs) have been widely used in clinical pratice, their control strategy is still a great challenge for researchers. The rotational speed of RBPs needs to be regulated carefully to achieve adequate perfusion for different patients and in the same patient for different conditions. When the RBPs are driven at aconstant speed, they cannot appropriately respond to the changes in preload and afterload, as compared with the native heart (1). In order to solve this problem, several control strategies have been designed. In 2004, Giridharan et al. designed a physiological controller that used the mean differential pressure between the left ventricle and the aorta as the control variable to regulate pump speed(2). Boston et al. designed a hierarchical controller, which regulated
doi:10.1111/j.1525-1594.2012.01511.x Received October 2011; revised May 2012. Address correspondence and reprint requests to Professor Yu Chang, School of Life Science and BioEngineering, Beijing University of Technology, Beijing 100124, China. E-mail: changyu@ bjut.edu.cn

the pump speed to ensure that the pulsatility of thepump flow signal remained in a normal range (3). Arndt et al. used the gradient of differential pressure pulsatility to classify two specific operating modes for a left ventricular assist device (LVAD): full or partial assistance (4). Wu proposed a physiological adaptive controller, which calculated the change of peripheral resistance according to intrinsic pump parameters (pump speed and currentwaveform), and then regulated the pump speed according to the change of peripheral resistance (5). In order to improve the robustness of the controller, Chang and Gao reported a global sliding mode controller for an intra-aortic pump (6). This controller is insensitive to changes in circulatory parameters such as resistance and compliance of the peripheral vessel. Moscato et al. proposed a...