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 bre athing subjects were represented graphically as (1) raw RR interval time se ries, (2) RR consecutive difference time series and (3) a phase portrait of the RR consecutive difference time series. We then examined the relationsh ips between the presence of cardioventilatory coupling in these epochs and the plot appearance and entropy measures derived from these plots. We obser ved 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 R R consecutive difference time series and its phase portrait. We conclude th at, with some provisos, these simple graphical and derived quantitative mea sures provide a basis for the determination of cardioventilatory coupling f rom heart rate time series.