THORACIC CAGE IMPEDANCE MEASUREMENTS. CANCELLATION OF RESPIRATION EFFECTS ON TRANSTHORACIC IMPEDANCE,

Monitoring transthoracic electrical imedance related to cardiac activity has been hampered by changes in the measured impedance due to respiration. It is necessary to nullify respiration effects if a relatively undistorted cardiac activity waveform is to be recorded continuously during respiration. Both direct filtering and subraction of the respiration signal from the composite respiration-cardiac waveform were considered. Methods used to obtain a respiration signal for subtraction purposes were based on 1 a chest circumference measurement obtained with a bellows and pressure transducer, 2 the detection of an impedance change due solely to respiration, and 3 the utilization of the phase-angle signal associated with the transthoracic impedance. Promising results were obtained when the phase-angle signal was combined with the composite respiration-cardiac waveform. The effect of repiration impedance change on the resulting waveform was less than 50 of the cardiac activity signal under restingbreathing conditions. Author