Abstract
An automatic control system is proposed for respiratory failure patients under artificial ventilation. The whole control system is designed as a 2-input 2-output system based on an adaptive pole-assignment method. In this study, ventilation rate and inspired O2 tension are chosen as the input values, alveolar CO2 tension and arterial O2 saturation as the controlled values. The control system is divided into two subsystems: one is the control system of alveolar CO2 tension and the other is the control system of arterial O2 saturation. It is not so difficult to control alveolar CO2 tension, because the dynamic characteristics of alveolar CO2 tension are described as a 1-input 1-output system. On the other hand, it is rather difficult to control arterial O2 saturation, because the dynamic characteristics of arterial O2 saturation are described as a 2-input 1-output system, including the cross effects of ventilation rate and inspired O2 tension on arterial O2 saturation. Hereby, the dynamic characteristics of arterial O2 saturation are assumed to be represented by a 2-input 1-output mathematical model. Then, the effect of ventilation rate on arterial O2 saturation is regarded as an offset term. In which case, the proposed method makes the control system of arterial O2 saturation a 1-input 1-output system including the effect of ventilation rate. The effectiveness of the proposed control system is confirmed using a dynamic mathematical model of a human respiratory system, in both conditions of rest and a changing metabolic state..
