Reasearch On Lower Leg Edema Measuring System And Application Baseed On Biomedical Impedance

Edema refers to the swelling of a tissue that results from excessive accumulation of fluid within the tissue, which is typically the pathological process process of some disease, for example, heart failure. Therefore, the detection of edema is important for clinical application. Nowdays, clinical diagnosises of edema are varied according to different positions, most of which are too subjective or expensive, such as pressing the edema area or X-rays. Bio-impedance thchnique is becoming an effective method for the detection of edema, which is low-cost, non-invasive, safe and informative.Two aspects of work have been done base on the research at China and abroad about bio-impedance and edema diagnosis. A bio-impedance measurement system of high accuracy was designed and experiments were further carried out, establishing the relationship between edema and bioimpedance.Four eldectrodes method was used in bioimpedance measurement system with two electrodes for current injection and two others for voltage measurement. The amplitude and phase were measured by Amplitude & Phase Detecting with signal from voltage measurement electrode and reference signal. The hardware circuit involes current stimulation circuit, front-end processing circuit, amplitude and phase detection circuit and bluetooth communication circuit. Software design mainly includes AD9838 driver which generate security current. Calibration are implementated to improve the measurement accuracy of the system. The measured data transferred to android client via bluetooth were showed and storage for further procession. To test the, this problem is solved by the bioelectrical impedance measured by the R-C three-element circuit was implemented to measure the accuracy of this system. Amplitude relative error of the system is 2%, while the absolute phase error is 0.9 degrees.10 patients with different level edema were measured using this system before and after hemodialysis. The result showed that with the increase of hemodialysis time, the amplitude became larger at different frequencies, which was more obvious in lower frequencies. Base on this rule, ectracellular impedance value was fitted by Cole model o show the impedance change at the extreme. Besides, it showed that the higher the degree of the edema, the greater the rate of change of extracellular impedance, so the rate of change of extracellular impedance can be used as an indicator to evaluate the degree of edema, which is very promising in clinical applications.