Removal of respiratory artifacts from cardiogenic impedance signal by digital filtering

The use of a digital high-pass filter designed and implemented on a personal computer for thoracic impedance cardiography (ZCG) is discussed. Two male subjects were tested under supine, sitting and 50-W exercise conditions. The first derivative of the thoracic impedance signal was recorded by a standard four-electrode impedance cardiograph. The digital high-pass filter automatically selects its cutoff frequency (CF) as a fraction of the heart rate. It was determined that a fractional value of 0.35 provides the best elimination of breathing artifacts with minimal effect on the cardiac signal