Cardioventilatory coupling in heart rate variability: methods for qualitative and quantitative determination.

In this study we sought to develop quantitative methods for determining the presence of cardioventilatory coupling in raw heart rate time series. The beat-to-beat RR interval time series of 98 anaesthetized, spontaneously breathing subjects were represented graphically as (1) raw RR interval time series, (2) RR consecutive difference time series and (3) a phase portrait of the RR consecutive difference time series. We then examined the relationships between the presence of cardioventilatory coupling in these epochs and the plot appearance and entropy measures derived from these plots. We observed that coupling was significantly associated with the presence of banding in the raw heart rate and RR consecutive difference time series, and with discrete clustering within the RR consecutive difference phase portrait. A significant correlation was found between coupling and the entropy of the RR consecutive difference time series and its phase portrait. We conclude that, with some provisos, these simple graphical and derived quantitative measures provide a basis for the determination of cardioventilatory coupling from heart rate time series.