Movement artefact rejection in impedance pneumography using six strategically placed electrodes

In this paper, we have proposed a technique for reducing movement artefacts in impedance pneumography by placing six electrodes at appropriate locatio ns and suitably combining the measurements obtained. The strategy for elect rode placement was based on the observation that the electrodes appeared to slide over the rib cage along with the skin, during movement. A volume con ductor model of the thoracic cavity was developed and movement artefacts we re simulated by shifting the electrodes to a different location on the surf ace. The impedance changes due to movement in one of the measurements of a 'symmetrical pair' were 180 degrees out of phase with respect to those obse rved in the other measurement of that pair. However, the impedance changes due to breathing were in phase in both these measurements. Thus, it was pos sible to reduce movement artefacts by taking a mean of these measurements w ithout affecting the breathing related changes. The six electrodes could be configured into two such symmetrical pairs. The same observation was made in experimental data recorded from human subjects. This indicated that move ment artefacts were caused by sliding of electrodes along with the skin and could be reduced by using the six-electrode configuration.