Measurement Method and Principle for Thoracic Impedance Graph

Abstract

Thoracic impedance graph is an impedance change curve measured on the surface of the human chest. It reflects indirectly the volume change of the heart and large vessels in the thorax, and it includes rich information about physiological activities and pathological changes. Thoracic impedance graph is measured using the four-electrode method in this article. Thoracic impedance change is transformed to the voltage change by means of the high frequency current Io, with a constant root-mean-square (rms) current. The voltage change which is directly proportional to thoracic impedance change can be obtained through the amplification, detection and calibration. The direct proportional relationship between the thoracic impedance change and volume change of the blood vessels is deduced by means of the thoracic parallel impedance model.