Signal fidelity requirements in determining measures of cardiac function — Advancing to multichannel impedance cardiography

Cardiac output (CO) is one of the core parameters in assessing the status of the heart. Impedance cardiography (ICG) has been introduced in the 1960's as a simple and noninvasive measurement of CO. However, measured data remain controversial, leading sometimes to errors and discouraging utilization of the approach. This work presents an investigation of the measurement properties of new ICG measurement configurations based on computerized application of the lead field theory in realistically shaped volume conductor models of the human thorax. Preliminary clinical experience was acquired by making recordings in healthy volunteers and valve patients. To improve reliability of ICG, a large number of different measurements should be taken and analyzed instead of a single signal as in conventional ICG. Comparison of simulations with parameters derived from clinical data correlated favorably, indicating the potential of the theoretical method in developing ICG measurement configurations. Moreover, clinical data suggested the likelihood that determination of different parameters — whether standard ones such as CO or derived indices approximating cardiac function — can be based more solidly on physiological principles and not only on experimental data, although the multiregional signal origin remains. For more advanced experiments and signal analysis, a multi-channel ICG device should be implemented.