Automatic control of extracorporeal life support.

摘要

The research described in this thesis addresses a conceptual and experimental design of an automatic controller for a life support system for temporary maintenance of gas exchange and perfusion for patients with life-threatening cardiopulmonary function insufficiency. Such a controller is expected to represent a significant improvement over the current manually-controlled extracorporeal life support (ECLS) system in adapting to varying gas exchange and perfusion needs during the period of support, and in automatically weaning the patient from support upon improvement in cardiopulmonary function.; Two subsystems were defined for control of gas exchange in ECLS. One control system adjusted ECLS blood flow rate to maintain adequate oxygen delivery relative to oxygen consumption, as indicated by the mixed venous oxyhemoglobin saturation. The other controller adjusted gas flow through the gas exchanger to maintain a desired value of the partial pressure of carbon dioxide in mixed venous blood. Properties of the plants were examined during in vivo experiments that investigated steady state and dynamic properties of the relationships between oxygen delivery, carbon dioxide removal, and ECLS parameters, specifically extracorporeal blood flow rate and gas flow rate in the oxygenator.; A theoretical model of the patient plus ECLS system was designed based on knowledge of physical characteristics of the system, and included variables to account for variations between patients and ECLS configurations. Numerical values for the variable model parameters were obtained by comparing simulations of the model with experimental data. Digital control algorithms were designed using simulation of the closed loop control system. The effects of model uncertainty on performance and stability of the control system were evaluated through simulation over the range of uncertainty in model parameters.; The control system was implemented in hardware and software. The oxygen delivery controller was evaluated during animal experiments, where interventions were made that altered native oxygen delivery and consumption. The controller was shown to be effective in adjusting ECLS blood flow to compensate for fluctuations in the supplemental oxygen delivery requirements of the animal, and demonstrated a significant improvement over the manually-adjusted ECLS system.