The Preliminary Research On Detection Of Pulmonary Edema With Multi-frequency Transthoracic Electrical Bio-impedance

Pulmonary edema is a syndrome resulted from the raising of extra-vascular lung water. There are about 10% varies of patients suffering from pulmonary edema before they are dead. Therefore, it's very important for serious patients to detect and cure the pulmonary edema on the early phase.Following is the theory of the detection of pulmonary edema by transthoracic electrical bio-impedance, while there is a pulmonary edema disease, the circulation of blood and respiratory condition will change, which results in the change of the transthoracic bio-impedance. By detecting the impedance and its changes, we can diagnose the disease. Because this technology is non-invasive, portable, simple to use and possible for continuous monitoring, there is great prospect of the detection on pulmonary edema by transthoracic electrical bio-impedance.Based on this theory, we designed the multi-frequency transthoracic electrical bio-impedance detection system; and finished preliminary experiment. Following is the main content:1). developed multi-frequency exciting source based on directdigital synthesis technology, which can output constant current signal from 10KHz to 200KHz.2). designed phase shift circuit based on Phase Locked Loop technology and demodulating circuit based on multiplier. Obtained the real-time signals of phase and amplitude.3). Developed soft system by LabWindows/CVI. Designed sweeping-frequency mode and single-frequency mode.4). Finished debugging, scaling and verifying by measuring the resistor-capacitor system. Measured the normal person's transthoracic electrical bio-impedance and analyzed several factors that affect the body measurement.5). Designed the animal experiment. Obtained the animal model which affected pulmonary edema by induced oleic acid. Detected and analyzed the change of transthoracic electrical bio-impedance resulted from the pulmonary edema disease.In this study, we completed the multi-frequency transthoracic electrical bio-impedance detection system. The result of the experiment indicated that multi-frequency system can obtain more obvious and more impedance parameters that could reflect the pulmonary edema. Compared with the traditional single-frequency technology, multi-frequency technology was superior.Finally we analyzed the measurement system and the experiment, and presented some advice of improvment.