RESUMEN
PURPOSE: The aim of the present study is to investigate an impedance change equation suited with the measurement of the impedance cardiograph (ICG). METHODS: Based on a parallel impedance model and Ohm's law, an impedance change equation differed from Nyboer's equation is deduced. It is verified with the experiments of the impedance cardiography in 100 healthy adults. RESULTS: This equation shows that the thoracic impedance change (ΔZ) is directly proportional to the value of the volume change (ΔV) of the blood vessel, to the ratio of the basic impedance to the body height (Z(0)/H), while it is inversely proportional to the square of the chest circumference (C(t) (2)). These are supported by the experimental results in the measurement of the ICG. CONCLUSIONS: The equation proposed in the present paper is coincident with the actual condition in the measurement of the ICG.