A control strategy of intra aorta pump based on blood assist index / 医用生物力学

Objective A blood assist index (BAI), defined as ratio of the output power of LVAD (left ventricular assist device) to the total input power of circulatory system, was proposed in this paper to regulate the energy distribution between LVAD and natural heart. Methods A control strategy based on model free adaptive control (MFAC) algorithm was designed by using BAI as the control variable. The algorithm could track the desired BAI by regulating the pump speed to maintain the measured BAI. A mathematic model of cardiovascular system was used to verify the feasibility of the controller in presence of heart failure, slight physical active and recovery of cardiac function. Results The simulating results demonstrated that the proposed controller could automatically regulate the pump to respond to the reduced peripheral resistance (5 500 r/min vs. 6 000 r/min). When Emax increased from 80 to 240 Pa/mL to simulate the heart recovery, the blood flow rate could increase accordingly from 5 to 8 L/min.Conclusions The proposed control strategy can provide an adjustable and accurate energy distribution between LVAD and native heart by regulating the pump speed, which would be of benefit to promoting left ventricle reverse remodeling.

Design of a global sliding mode controller for intra-aorta pump / 医用生物力学

Objective To design a global sliding mode control algorithm for the purpose of eliminating the chattering effect in conventional sliding mode control algorithm on both the controller and controlled plant from the conventional sliding mode control algorithm and regulating the intra aorta pump in response to the demand of blood circulation system in human. Methods A dynamic disturbance compensator was used to estimate the uncertainty of the intra aorta pump control system. Computer simulations and in vitro experiments were also conducted to verify the dynamic characteristics and robustness of the controller. Results As the dynamic disturbance compensator was used to estimate the uncertainty of system, the chattering effect in sliding mode control algorithm was eliminated. When the reference flow rate was set at 5 L/min, the response time was 80 ms without any overshot and static error. When the load torque of the controller was increased to 0.4 N·m, the response time was 25 ms. When the pulsatile signal was input as the reference flow rate, the dynamic response time was 80 ms with the maximum error of flow rate being 0.03 L/min. In the in vitro experiments, as the feedback frequency of flow rate signal and pump speed signal were lower than that in the ideal condition, the controller performance was deteriorative compared with computer simulation. The experimental results demonstrated that when the reference flow rate was set at 5 L/min, the response time was 0.26 s with the error of flow rate being 0.1 L/min. Conclusions The controller provided in this paper can accurately regulate the intra aorta pump according to the reference flow rate. Furthermore, it has a strong robustness for the uncertainty and disturbance of the control system. Due to the use of dynamic disturbance compensator, the chattering effect of the algorithm has been eliminated.

Research on lumped parameter model based on intra-aorta pump / 医用生物力学

Objective Try to set up a nonlinear lumped parameter model of intra-aorta pump by studying the relationship between the pressure difference and the blood flow rate at the head of the pump, so as to predict the hemodynamic parameters of the pump. Methods Only the parameters of the pump, without hemodynamic parameters of the circulating system, were used to esfablish the model. It was composed of a speed-controlled current source representing the flow rate driven by impeller, an internal resistant representing the resistance of the radial clearance, an inductance denoting the inertance of the blood. Results The model could simulate the physiological status of the heart under all the situations from pulmonary congestion to ventricular collapse. The characteristic equation of the pump was derived with parameters determined by experimental data in vitro. Conclusions To verify the accuracy of the model, the prediction value calculated from the model was compared with the one recorded from experiment in vitro. The results showed that the error in between was less than 5%, which indicated that this model could predict the pressure difference of the pump accurately.