Abstract
Fuzzy blood pressure control system has been developed to regulated blood pressure by using vaso-active drugs, which aims the medical treatment of the patient. Fuzzy logic is used to convert heuristic control rules as a physician's knowledge into an automatic control strategy. Usually, a physician decides infusion rate based on referring ideal pressure trajectory during control. To emulate such a physician's heuristic control, the controller refer an ideal pressure trajectory, for example, from the normal level to the target level. One of Inputs to the controller is a difference between real pressure and ideal pressure, where another is a rate of its pressure difference. An output from the controller is the change in drug infusion rate. Both of inputs and output are transformed into fuzzy sets, whose membership functions are predefined. Twenty one physician's control rules are converted into fuzzy control rules. The fuzzy control procedure consists of three steps: (1) computing both input values and finding their appropriate membership values (grade), (2) finding applied rules and applying fuzzy composition to infer weighted output fuzzy sets, (3) inferring the change in drug infusion rate by taking the center of mass of the membership function of output. Nine animal experiments are performed to evaluate the developed system by using rats with vasopressor drug, Angiotensin II Blood pressure was elevated from normal pressure (around 100mmHg) to 150mmHg. Satisfactory blood pressure control was realized on eight experiments and effectiveness of the controller was confirmed. The fuzzy control approach is especially useful for the closed-loop control in the medical fields, because the knowledge of expert physician's treatment is directly contained and represented in the control strategy. The system is expected to be applicable to the clinical cases.
