| The total thoracic impedance (4, ~) )is the resistance of intrathoracic tissue to alternating current, which reveals the hydration of intrathoracic tissue. Cell has different resistance to different frequency current. Thus, the full-scale intrathoracic hydration cannot be demonstrated only by single frequency impedance. Objective To develop a frequency-switching impedance apparatus then applying it to explore the feasibility of noninvasive-monitoring of pulmonary edema and theoretical foundation. Methods A frequency-switching impedance apparatus was developed which could produce constant currents at frequency of 25KHz~ 5OKHz~ 100KHz.. 200KHz. With the apparatus, investigation of Z0 in adults and overall observation of the Z0 trend in cardiogenic and oleic acid edema of canine were carried out. Results 1. Scurity and accuracy of the apparatus stood the test. 1. Normal adults investigation (1)4 of different frequency in adult obtained. (2) There was a minus correlation between Z0 and frequency and 4 was influenced by posture, lead, and sex. (3) There was a minus correlation between 4 of 200KHz and body weight in head lead. (4) Impedance ratio was independent of posture. 2.Observation of experimental canine pulmonary edema (1) Z0 of different frequency in canine obtained. (2) Z0 step down during acute cardiogenie pulmonary edema. 3 (3) No relationship was found between Impedance ratio and pulmonary edema. Conclusioui 1. 4 must be connected with specific frequency. 2. 4 of different frequency in adult and anaesthetic canine obtained. 3. 4 steps down during acute cardiogenic edema in experimental canine. 4. There is a potential prospect of 4 in monitoring pulmonary edema yet further researches needed.
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