Analysis of respiratory sinus arrhythmia with respect to respiratory phase

We evaluated the respiratory modulation of heart rate, i.e,, respiratory si nus arrhythmia (RSA), with respect to respiratory phase derived from an ana lytic signal from the lung volume curve, during spontaneous breathing and p aced breathing with different patterns. The magnitudes and waveforms of RSA in the phase domain were similar regardless of breathing pattern, even inc luding spontaneous breathing. An examination of the occurrence of heart bea ts with respect to the respiratory phase revealed that synchronized pattern s recently reported in the literature (Nature 392, 239, 1998) were observed during paced breathing with breath holding periods whereby the respiratory phase advanced more slowly. It was concluded that the phase domain approac h might be useful in extracting RSA during spontaneous breathing and for el ucidating detailed mechanisms for RSA. However, the use of this technique f or studies investigating cardio-respiratory coupling should be approached c autiously, as the results may be influenced by breathing patterns.