Studies On Hierarchical Control Strategy Of Artificial Heart For Cardiac Function Recovery

H’eart failure (HF) is a seirous disease that threatens humans health. Hearttransplantation and artificial heart are the main treatments for advanced HF. Due tothe shortage of donor heart, artificial heart has received great attention and thus hasdeveloped rapidly. With the extensive use of the artificial heart in HF treatment, thephenomenon of cardiac function recovery caused by artificial heart has attractedintensive attention worldwide. However, previous studies concerning how to promotecardiac function recovery by artificial heart still have no clear conclusion.This paper aims to promote cardiac function recovery by controlling artificialheart. A hierarchical control strategy of artificial heart was established to promotecardiac function recovery and addressed the following three research questions withrespect to the treatment of HF by using artificial heart.1) How to determine theoptimal support level?2) How to satisfy the requirements of circulatory bloodperfusion and cardiac unloading?3) How to maintain the control stability of artificialheart system?First of all, the cardiovascular-pump system coupled model was established toprovide the controlled plant for artificial heart control strategy. The lumped parametermodel of the circulatory system was established to reflect the circulatory systemhemodynamic mechanism. The mathematic model of baroreflex system wasestablished based on the adjustment mechanism of baroreflex system. Thehydrodynamic model of the artificial heart was established to mimic the fluidproperties of the artificial heart. Then the cardiovascular-pump system coupled modelwas established by coupled the above-mentioned three models. The accuracy of thecoupled model was evaluated by numerical method.Secondly, the artificial heart hierarchical control strategy was established to solvethe three aspect problems during supported by artificial heart. First, the outer layercontrol strategy was designed by using the baroreflex sensitivity (BRS) to determinethe optimal circulatory support level. Second, the middle layer control strategy wasdesigned in this paper to satisfy the requirements of circulatory system bloodperfusion and cardiac unloading. The heart rate was used to indicate the metabolicchanges of circulatory system, and the blood assist index (BAI) was designed toreflect the cardiac unloading level. The heart rate and BAI were both chosen as control variables for the middle layer control strategy to satisfy the requirements of bloodperfusion and cardiac unloading by adjusting support level. Third, the inner layercontrol strategy was designed to diminish the effects of internal uncertainty andexternal disturbance on artificial heart system. Finally, the artificial heart hierarchicalcontrol strategy was designed by coupled the above-mentioned three control strategies.And then the stability and performance of the hierarchical control strategy wereevaluated by using numerical study, in vitro experiment and animal experiment.Thirdly, the issues on the change of blood pulsatility caused by artificial heartand the hemodynamic effects of support mode on circulatory system wereinvestigated by using numerical method. First, the pulsatility control strategy wasdesigned to compensate the change of circulatory system blood pulsatility. Second,the constant speed support mode, co-pulse mode and counter-pulse mode weredesigned, and their hemodynamic effects on the circulatory system were explored byusing numerical method.Three conclusions were obtained:1.The cardiovascular-pump system coupled model established in this paper couldmimic the change of hemodynamic states of circulatory system under differentsupport level of the artificial heart.2.The artificial heart outer layer control strategy proposed in this paper coulddetermine the optimal support level according to BRS with the settling time lessthan5s. The middle layer control strategy could satisfy the requirements ofcirculatory system blood perfusion and cardiac unloading. The inner layer controlstrategy was able to diminish the effects of uncertainty and disturbances onartificial heart system with the maximum static error less than O.lL/min. Thehierarchical control strategy is sufficient to solve the above three problems andthe setting time was less than5s with the maximum error of the lfow rate beingabout O.lL/min. Moreover, the animal experiment demonstrated that hierarchicalcontrol strategy could accurately determine the optimal support level, and it couldprovide an optimal solution for the requirements of blood perfusion and cardiacunloading, and the control strategy have more rubustness for the internaluncertainty and external disturbance.3.The numerical simulation indicated that the hemodynamic characteristics of thecirculatory system were significantly affected by artificial heat support. On onehand, the designed pulsatile control strategy could compensate the change of circulatory system blood pulsatility. On the other hand, compared with theconstant speed support mode, the co-pulse support mode and counter-pulsesupport mode can achieve a better unloading effect. For co-pulse support mode, itcould achieve a better pressure unloading as well as the minimum ventricularexternal work and maximum blood pulsatility; for counter-pulse support mode, itwas able to achieve a better volume unloading as well as the minimum leftventricular afterload.This study involves three innovations. To begin with, different from conventionalartificial heart control strategy, the methods of optimal cardiac support level andpromoting cardiac function recovery were proposed in this paper. Second, the outerlayer control strategy was designed to achieve the optimal cardiac support level forcardiac function recovery. The blood assist index (BAI) was proposed to evaluate theventricular unloading level. The middle layer control strategy was designed to balancethe requirements of blood perfusion and cardiac unloading. The inner layer controlstrategy was proposed to maintain the control stability of the system. Third, the invitro, animal and clinical experiment demonstrate that the proposed control strategycould satisfy three requirements including achieving optimal support level, balancingthe requirements of blood perfusion and cardiac unloading as well as maintainingcontrol stability of system. The proposed control strategy could achieve the normalfunction of circulatory system and has been successfully used in4clinical cases untilnow.