Estimation of the respiratory activity from orthogonal ECG leads

In the present work a method is proposed for the estimation of the respiratory signal from the three ECG orthogonal leads. The vectorcardiogram loop was evaluated in correspondence of each QRS complex (in a time window of 120 ms centred around the R wave). The centre of gravity and the inertial axes of each loop were calculated. A set of 12 parameters (3 spatial coordinates of the centre of gravity and 3 directions of the 3 inertial axes) was obtained for each cardiac beat. The first principal component of such a set of data was the estimation of the respiratory activity. The obtained signal was compared with the quantitative respiration recording and the cross-correlation index C was a measure of the goodness of the estimation. The mean value of C was 0.9 ± 0.26, indicating a good matching between the recorded and the estimated signals.