Fuzzy control of high frequency ventilation

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The main results of this research are divided into three parts; (1) a possible mechanism of high frequency ventilation (HFV), (2) a new method applying HFV and (3) a fuzzy control system of HFV.1. The possible mechanism of HFV Velocity profiles of oscillatory flows in a cylinder have been measured using a laser Doppler velocimeter. The velocity profile has been asymmetric with respect to the direction of the flow under certain conditions. This result implies that mass transport occurs even if volumes flowing into the cylinder is identical with those flowing out of it.2. The new method applying HFV A mechanical oscillating system consisting of a spring and a mass is driven by a centrifugal force resulting from unbalanced rotation. A parallel leaf spring restricts the freedom of the oscillation to one dimension. The oscillating system can generate relatively large oscillations by a low power motor with a small power, and it also ensures the safety of patients because the generated flow rate has an upper limit.3. The fuzzy control system of HFV A system using the fuzzy PI control rule has been designed to maintain a normal partial pressure of CO_2 in arterial blood (p_aCO_2). The inputs of the system are the error of p_aCO_2 (the deviation from the reference, 40 mmHg) and the change in the error; the output is the change in the rotation of HFV. The fuzzy compositional rule of inference produces the output fuzzy set from the inputs. The output fuzzy set is defuzzyficated by the so-called "center of mass" method to give the output. The experiment using dogs have shown that the control system can restore p_aCO_2 to the neighborhood of 40 mmhg when p_aCO_2 is disturbed. This result indicates that fuzzy control systems can be used for HFV. It is one of their advantage that they do not need the dynamic characteristics of HFV in detail.