Seongjin Choi

A sensorless approach to control of a turbodynamic left ventricular assist system

A fuzzy logic controller for a rotary, turbodynamic left ventricular assist system was developed to optimize the delivery of blood flow without inducing suction in the ventricle. The controller is based on the pulsatility in blood flow through the pump and assumes that the natural heart is still able to produce some pumping action. To avoid the use of flow transducers, which are not reliable for long term use, the controller estimates flow using a model of the assist device. The controller was tested in computer simulation, a mock circulatory system, and in animal experiments. Simulation studies suggest that the fuzzy logic controller is more robust to parameter changes than a traditional proportional-integral controller. Experimental results in animals showed that the controller is able to provide satisfactory flows at adequate perfusion pressures while avoiding suction in the left ventricle.

Modeling and identification of an axial flow blood pump

This paper presents a model for identification of an axial pump. It aims to provide flow and pressure difference estimates of the axial pump as well as the parameters of the pump characteristics without using flow and pressure sensors.

Intelligent control design for heart assist devices

Heart assist devices are blood pumps used to augment the cardiac output of patients with left ventricular failure. A new generation of devices being evaluated for human use is based on turbo-hydrodynamic methods of pumping, which offer several advantages over the reciprocating, pulsatile methods used in current devices. However, the new devices pose a more difficult control problem because of their sensitivity to circulatory load and other patient cardiovascular parameters. The paper describes the design of a control structure to regulate the operation of these devices. The controller has three different types of algorithm available: a model-based patient-adaptive algorithm; two heuristic algorithms that rely only on the device characteristics; and a default algorithm. The patient-adaptive algorithm uses a model of the patients systemic circulation to determine the required cardiac output for a given level of activity. The heuristic algorithms use the known operating characteristics of the device to adjust the cardiac output to changes in demand without knowledge of patient-specific conditions. The default algorithm provides a fixed speed operation to be used in case of system or sensor failure. An intelligent supervisor determines the cardiac output required from the assist device and selects the control algorithm to use, based on a multidimensional measure of the patients level of activity, available estimates of hemodynamic variables, reliability of the patient model, and the past history of the patient.

Progress on development of the Nimbus-University of Pittsburgh axial flow left ventricular assist system

Nimbus Inc. (Rancho Cordova, CA) and the University of Pittsburgh have completed the second year of development of a totally implanted axial flow blood pump under the National Institutes of Health Innovative Ventricular Assist System Program. The focus this year has been on completing pump hydraulic development and addressing the development of the other key system components. Having demonstrated satisfactory pump hydraulic and biocompatibility performance, pump development has focused on design features that improve pump manufacturability. A controller featuring full redundancy has been designed and is in the breadboard test phase. Initial printed circuit layout of this circuit has shown it to be appropriately sized at 5 x 6 cm to be compatible with implantation. A completely implantable system requires the use of a transcutaneous energy transformer system (TETS) and a diagnostic telemetry system. The TETS power circuitry has been redesigned incorporating an improved, more reliable operating topography. A telemetry circuit is undergoing characterization testing. Closed loop speed control algorithms are being tested in vitro and in vivo with good success. Eleven in vivo tests were conducted with durations from 1 to 195 days. Endurance pumps have passed the 6 month interval with minimal bearing wear. All aspects of the program continue to function under formal quality assurance.