ABSTRACT
Physiological feasibility is the most important requirement for cardiovascular circulatory simulators (CCSs). However, previous simulators have been validated by a comparison with specific human data sets, which are valid only for very limited conditions, and so it is difficult to validate the fidelity of a CCS for various body conditions. To overcome this critical limitation, we propose a model-referenced CCS that reproduces the behavior of an electrical-analog model of the cardiovascular circulatory system, for which physiological fidelity is well established over a wide range. In this study, the electrical-analog reference model was realized in the hardware simulator using fluidic element modeling and by the feedback control of a mock ventricle. The proposed simulator showed a good match with the reference model behavior, and its physiological validity was thereby verified. The proposed simulator is able to show responsiveness to various body conditions as well. To the best of the author's knowledge, this is the first report of an in vitro CCS verified to be consistent with reference model behavior.
Subject(s)
Cardiovascular Physiological Phenomena , Cardiovascular System/anatomy & histology , Materials Testing/methods , Models, Anatomic , Models, Cardiovascular , Computer Simulation , Finite Element Analysis , Heart Valves/anatomy & histology , Heart Valves/physiology , Heart Ventricles/anatomy & histology , Heart-Assist Devices , Hemodynamics , Humans , Prosthesis Design , Reproducibility of Results , Ventricular FunctionABSTRACT
A safety-enhanced optimal (SEO) control algorithm for turbodynamic blood pump is proposed. Analysis of in vivo animal experimental data reveals that two new control indices-the gradient of pulsatility of pump pressure head with respect to pump speed and the gradient of minimum pump flow-have their peak within a proximity to the suction point but not at the exact suction point. They were also verified to satisfy the requirement of cost function for the extremum seeking control (ESC). New cost functions were tested for ESC to find and track the new operating point--SEO operating point--where sufficient cardiac perfusion and safety margin to suction is guaranteed. By computer simulation, it is confirmed that the SEO operating point was successfully found and tracked in both fixed and varying hemodynamic load scenarios using proposed control indices without resorting to a slope seeking control algorithm where the reference slope must be supplied.
Subject(s)
Heart-Assist Devices , Algorithms , Computer Simulation , Hemodynamics , Humans , Models, Cardiovascular , Prosthesis Design , Prosthesis FailureABSTRACT
Mock circulatory systems (MCS) are often used for the development of cardiovascular devices and for the study of the dynamics of blood flow through the cardiovascular system. However, conventional MCS suffer from the repeatability, flexibility, and precision problems because they are typically built up with passive and linear fluidic elements such as compliance chamber, manual valve, and tube. To solve these limitations, we have developed an impedance simulator, comprised of a feedback-controlled positive displacement pump that is capable of generating analogous dynamic characteristics as the conventional fluidic elements would generate, thereby replacing the conventional passive fluidic elements that often cause problems. The impedance simulator is experimentally proven to reproduce the impedance of the various discrete elements, such as resistance and compliance of the cardiovascular system model, as well as the combined impedances of them.
Subject(s)
Biomimetic Materials , Coronary Circulation/physiology , Models, Cardiovascular , Vascular Resistance/physiology , Ventricular Function/physiology , Blood Flow Velocity , Computer Simulation , Computer-Aided Design , Equipment Design , Equipment Failure Analysis , Feasibility Studies , HumansABSTRACT
Ventricular assist devices now clinically used for treatment of end-stage heart failure require responsive and reliable control to accommodate the continually changing demands of the body. However, due to the varying physiologic conditions and the limited use of the sensors to detect hemodynamic load and suction, it is difficult to control pump speed appropriately. The author introduces an adaptive pump speed controller to provide maximum cardiac perfusion while avoiding ventricular suction. The controller is based on an extremum seeking control (ESC) algorithm and a slope seeking control (SSC) algorithm, which find and track unknown and moving peak points of a prescribed cost function. The controller was validated with in vivo data using time-averaged diastolic pump flow as the cost function for ESC/SSC. Initial results demonstrate the successful application of ESC/SSC as a physiologic pump speed controller.
Subject(s)
Algorithms , Heart-Assist Devices , Coronary Circulation , Equipment Design , HumansABSTRACT
Ventricular assist devices now clinically used for treatment of end-stage heart failure require responsive and reliable hemodynamic control to accommodate the continually changing demands of the body. This is an essential ingredient to maintaining a high quality of life. To satisfy this need, a control algorithm involving a trade-off between optimal perfusion and avoidance of ventricular collapse has been developed. An optimal control strategy has been implemented in vitro that combines two competing indices: representing venous return and prevalence of suction. The former is derived from the first derivative of diastolic flow with speed, and the latter derived from the harmonic spectra of the flow signal. The responsiveness of the controller to change in preload and afterload were evaluated in a mock circulatory simulator using a HeartQuest centrifugal blood pump (CF4b, MedQuest Products, Salt Lake City, UT). To avoid the need for flow sensors, a state estimator was used, based on the back-EMF of the actuator. The multiobjective algorithm has demonstrated more robust performance as compared with controllers relying on individual indices.
