Respiration affects on P wave alignment and averaging

Root-mean-square values of the residual signals between a P wave template and individual P waves were computed and a tachogram was made. Using Autoregressive (AR) modelling, a major spectral peak was observed at 0.2 Hz for both this tachogram and the respiratory volume signal. A similiar spectrum was obtained from the RMS tachogram of the isoelectric signal segments prior to the P waves. When the lead signals were filtered (6–12.5 Hz), the energy in the RMS tachogram of the isoelectric region almost vanished. On the other hand, volume gated signal averaging of the P waves led to two distinct averages corresponding to high and low respiratory volume. The difference was in the form of up to 10% amplitude scaling.