Decomposition of the Cardiac and Respiratory Components from Impedance Pneumography Signals

Impedance pneumography (IP) measures changes of thoracic electrical impedance connected with change of the air volume in the lungs. The electrode configuration used in IP applications causes that electrical heart activity is visible in the IP signals. The aim of this paper is to assess the opportunity to decompose both respiratory and cardiac components and its quality using various methods. Ten students performed static breathing sequences, intended both for calibration and testing. Our prototype, Pneumonitor 2, and the reference pneumotachometer, were used. The accuracy of calculating tidal volume and heart rate, the calibration procedure and the time of analysis, were considered. Mean 86.5% accuracy of tidal volume calculating and only 2.7% error of heart rate estimation were obtained using moving average smoothing filters, for simple short recording of free breathing calibration procedure, in three body positions. More sophisticated adaptive filtering also provided good accuracy, however the processing time was 100-times higher, compared to simple methods. It seems impedance pneumography, without ECG, could be enough for measuring basic cardiorespiratory activity, particularly during ambulatory recordings, in which the least disturbing equipment is desirable.