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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.

The purpose in this article is to investigate the measurement method and normal values of the total peripheral resistance (TPR) and total peripheral resistance index (TPRI) measured by the reconstructed impedance cardiogram (RICG). Methods The cardiac output and cardiac index of 180 normal adults is measured by means of the RICG. The computed formula of the TPR and TPRI are deduced, and the TPR and TPRI are calculated. The subjects are divided to the different groups according to the sex and age. The TPR and TPRI are calculated statistically. Results The TPR and TPRI are increased with the increase of the age, and there is significant difference between the young and elder groups (P0.05). The normal value of the TPR is less than 1650 dyn.s.cm-5, and that of the TPRI is less than 2650 dyn.s.cm-5.m2. Conclusion The TPR and TPRI measured by the RICG can reflect the hemodynamic changes of the normal or abnormal body.