Design and implementation of a digital filter for beat-by-beat impedance cardiography

A digital filter for thoracic impedance cardiography was developed and implemented on a 16-bit personal computer after examining the effect of respiratory movement on the first derivative of the thoracic impedance signal. Four male subjects exercised with a cycle ergometer at 100 and 150 W successively, after resting for 5 min. Thoracic impedance and its first derivative (dZ/dt) were recorded by a standard four-electrode cardiograph. The peak-power spectral densities of the pneumogenic (P _p,c) and the cardiogenic (P _p,c) components of dZ/dt were separated with a simultaneous recording of the ECG and thoracic circumferences. P _pP _c increased with each increment of work rate: 0.12 (0.05-0.19) at rest, 0.67 (0.49-0.97) at 100 W, and 0.97 (0.58-1.52) at 150 W.