Cardioventilatory coupling in heart rate variability: the value of standard analytical techniques

In a group of spontaneously breathing anaesthetized subjects, we examined t he ability of simple spectral and non-linear methods to detect the presence of cardioventilatory coupling in heart rate time series. Using the proport ional Shannon entropy (HRI-I) of the RI-I interval (interval between inspir ation and the preceding ECG R wave) as a measure of coupling, we found no c orrelation between HRI-I and either the fractal dimension or approximate en tropy of the heart rate time series. We also observed no difference in the distribution of heart rate variability (HRV) spectral power in three freque ncy ranges (high, 0.15-0.45 Hz; low, 0.08-0.15 Hz; very low, 0.02-0.08 Hz) between uncoupled epochs and coupling patterns I, III and IV. Because of it s association with low breathing frequencies, pattern II coupling epochs sh owed exaggerated low-frequency power as the high-frequency 'respiratory' pe ak fell into the low-frequency range. We conclude that coupling pattern is largely independent of autonomic tone and that these standard methods of HR V analysis are limited in their ability to detect the presence of cardioven tilatory coupling in heart rate time series.