Kwan-Woong Gwak

In Vitro Evaluation of Multiobjective Hemodynamic Control of a Heart-Assist Pump

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.

Experimental Verification of the Feasibility of the Cardiovascular Impedance Simulator

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.

Application of extremum seeking control to turbodynamic blood pumps.

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.

Safety-Enhanced Optimal Control of Turbodynamic Blood Pumps

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.

A Review of Steam Generation for In-Situ Oil Sands Projects

ABSTRACT Steam Assisted Gravity Drainage (SAGD), an unconventional enhanced oil recovery process for the oil sands, is getting more attention recently as the international oil price increases rapidly. Basic concept of SAGD is to extract the viscosity-lowered bitumen by high pressure, high temperature 100% quality steam injected into the reservoir containing high-viscosity bitumen. As its name implies, generation of high-quality, high-temperature and high-pressure steam is a prerequisite for the SAGD process. Hence in this paper, key aspects of steam generation system for oil sands recovery will be broadly reviewed to provide the engineers concerned with the working principles and the major issues such as configuration, design, control of steam generation system used for oil sands recovery.

Model-Referenced Cardiovascular Circulatory Simulator: Construction and Control

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 authors knowledge, this is the first report of an in vitro CCS verified to be consistent with reference model behavior.

Structural Analysis and Optimization of Nonlinear Control Systems Using Singular Value Decomposition

Structural information of a system/controller allows a designer to diagnose performance characteristics in advance and to make better choices of solution methods. Singular value decomposition (SVD) is a powerful structural analysis tool for linear systems, but it has not been applied to nonlinear systems. In this paper, SVD is used to structurally analyze and to optimally design nonlinear control systems using the linear algebraic equivalence of the nonlinear controller. Specifically, SVD is used to identify control input/output mode shapes, and the control input/output distribution patterns are analyzed using the mode shapes. Optimizing control effort and performance is achieved by truncating some mode shapes in the linear mode shape combinations. The proposed method is applied to the temperature control of a thermal system, and design guidelines are provided to overcome input-constraint-violating solutions.

Preliminary experimental results for neck injury in mobile robot-human constrained-collision

Following the increased use of mobile robots in the field, the injury problem caused by the collision between human and the mobile robot has become an issue of growing importance in the society. Neck injury is considered as one of the major injury mode in collision-induced injury. Hence in this paper, AIS of the neck injury was predicted using the index of neck injury on collision through the mobile robot-dummy collision tests.

Feedback Linearization Control of a Cardiovascular Circulatory Simulator

In this brief, a nonlinear model-based feedback linearization (FBL) control is proposed for a high-performance cardiovascular circulatory simulator (CCS). The challenges are that the piston pump used for a mock ventricle in CCS has high-bandwidth pressure dynamics and hard nonlinearity due to check valves. Limited control performance in the previous researches due to these difficulties even raises the question of the physiological feasibility of the developed CCS. To overcome this problem, FBL theory based on the Lie algebra is applied in this research for the piston pump mock ventricle control. Dynamic model of the piston pump was derived, and parameter values of the model were identified experimentally for the controller design. The experimental results confirmed good performance of the proposed controller for various physiological scenarios. Good match with the reference model behavior was verified as well, and physiological feasibility of the CCS was secured thereby thanks to the proposed high-performance controller.

In-vitro evaluation of multi-objective hemodynamic control of heart-assist pump

Ventricular assist devices (VADs) now clinically used for treatment of end-stage heart failure require responsive and reliable 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 tradeoff between optimal perfusion and avoidance of suction is 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 maglev centrifugal blood pump (CF4b, MedQuest Products). To avoid the need for flow sensors, an estimator is utilized, based on the back-EMF of the actuator. The multi-objective controller has demonstrated more robust performance as compared to controllers relying on individual indices.