Phase portraits of transfer systems - Non-linear transfer properties between respiratory movements and heart rate fluctuations

A new approach to the analysis of non-linear systems is proposed. It enables the reconstruction of the system state movement in a multi-dimensional phase space. The resulting phase portraits of the system behaviour were characterised quantitatively by estimating the correlation dimensions and prediction errors. This new approach was validated using simulated typical transfer systems. The measured respiratory movements and heart rate fluctuations of rabbits were employed for the first time to investigate the non-linear transfer properties between respiratory activity and heart rate in the system phase portraits. Significant non-linear transfer characteristics between respiratory movements and heart rate fluctuations were found - also during the awake phase which have so far not been quantified.