Control of artificial respiration by adaptive pole‐placement method

Most organic functions are described by complex dynamics of unknown and/or ambiguous subsystems characterized by their nonlinearity, chronic change and individual difference. Nevertheless, a respiratory regulation system among these subsystems is described by a bilinear mathematical model whose state variables are alveolar and average mixed venous CO2‐concentrations, and whose inputs are the ventilation rate of alveolus and metabolic rate converted into CO2‐volume. However, its nonlinear dynamic characteristics depend on time‐varying parameters, in particular, on the blood flow rate which varies on a large scale incidental to metabolic rate change. In this paper, an automatic control system of artificial respiration is discussed on the basis of the adaptive pole‐placement method using a linear mathematical model where the ventilation rate and alveolar CO2‐concentration are regarded as a controlling input and a controlled output, respectively. The feature of the proposed method is that desirable characteristics given beforehand by medical doctors can be realized automatically even with regard to individual difference and chronic change of characteristics seen distinctively in an organism. Here, to confirm the robustness of the proposed control system, a simulation experiment is given with some metabolic rate change as an input change regarding its contribution to the output as an effect of disturbance from an environment. Then the proposed method is applied to clinical experiments using a respirator controlled by outside signals. This respirator has been developed to meet the aim of the present study, resulting in good performance of dynamic characteristics of alveolar CO2‐concentration on healthy subjects.