Cardiac-Related Signal Extraction in Thoracic Impedance Measurement

Electrical impedance measurements in the thoracic region could be used to monitor the respiratory and the blood circulatory systems. The contribution of ventilatory-related signal (VRS) is 10 times greater, therefore most studies aimed at cardiac activity are made at short time breath hold. This paper presents an algorithm for extracting the cardiac-related signal (CRS) during free breathing. The advantage of the algorithm is its ability to preserve the beat-to-beat waveform. The algorithm allows to analyze the CRS and VRS simultaneously. This could significantly expand the possibilities to monitor cardiac indices and allows to study a complex interaction of the respiratory and circulatory systems using electrical impedance methods. The proposed algorithm could also be used to assess lung perfusion and estimate the ventilation-perfusion ratio. A measurement on a healthy volunteer was carried out to demonstrate the operation of the algorithm. A signal simulation is also provided to show a low level of distortion, that could be introduced by the algorithm.