Circuit model-based analysis of the impedance rheopneumogram.

Impedance rheopneumography, like other applications of electrical bio-impedance, is receiving increasing attention as a simple, non-invasive tool for clinical diagnosis of the pulmonary circulation. However, one major drawback of this method lies in the difficulty in computing accurately the time domain parameters therefrom for diagnostic purposes. This paper presents a model-oriented analysis technique based on physiological consideration of both the arterial and venous pathways of the pulmonary circulatory system. The technique involves a combination of a two-segment model and a modified form of the 'Windkessel' model, the summed response of which is curve-fitted to measurement data via the non-linear method of Marquardt to obtain the system parameters. A simple illustrative application is also given to explain the changes in wave morphology for a subject under measurement in the supine and sit-up positions. The result suggests that this technique shows promise of providing useful physiological information and better insight of system behaviour than existing technique.