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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 (Z0/H), while it is inversely proportional to the square of the chest circumference (Ct2). 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.

Purpose: The aim of the present study is to separate the impedance change components of the blood vessels and ventricles in thorax from the mixed impedance signals detected on the chest surface. Methods: The mixed impedance signals on the chest surface are measured with a 15 electrode lead system. The thoracic impedance equations are established and solved iteratively with the algebraic reconstructed technique. Experiments were performed on 80 healthy, otherwise normal, adults. Results: Five impedance change components for the aorta (AO), blood vessel in left lung (PL), blood vessel in right lung (PR), left ventricle (LV), and right ventricle (RV) are separated from the mixed impedance signals. The experiments show that the main waveform of the ventricular components LV and RV is contrary to that of the vascular components AO, PL, and PR, and the negative peak point of the waveform graphs of LV and RV are in phase with the second cardiac sound (S2). The waveform graphs of various components correspond with the physiological activities of the heart and blood vessels in a cardiac cycle. The statistical results for 80 normal adults show that the amplitude of AO is the largest and that of PL and PR is the next, while that of LV and RV is the smallest. There are significant differences between them (P < 0.01). Conclusions: The mathematical model and the measurement method for the separation in the present paper are feasible.

The aim of the present study is to investigate an impedance change equation suited with the measurement of the impedance cardiograph (ICG).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.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.The equation proposed in the present paper is coincident with the actual condition in the measurement of the ICG.