Table 3: Intercorrelations between metrics of mean HR, overall HRV, cardiovagal control, and cardiac sympathetic activity.

Mean HRSDNNCSIRSARMSSDpNN50HF-HRVLF-HRVHRDB

Mean HR
SDNN−0.465**
CSI0.543**−0.266*
RSA−0.519**0.864**−0.542**
RMSSD−0.590**0.867**−0.609**0.841**
pNN50−0.662**0.788**−0.670**0.857**0.922**
HF-HRV−0.252*0.822**−0.344**0.737**0.815**0.679**
LF-HRV−0.206*0.677**0.0280.467**0.450**0.356**0.428**
HRDB0.0750.494**−0.1580.553**0.413**0.407**0.433**0.344**

Note: Mean HR: mean heart rate; SDNN: standard deviation of interbeat interval (IBI); CSI: Toichi cardiac sympathetic index (sympathetic-related variability); RSA: natural log of variance of filtered (0.12–0.40 Hz) IBI; RMSSD: root mean square of successive differences between IBIs; pNN50: the percentage of the absolute differences between consecutive IBIs that are greater than 50 ms; HF-HRV: high frequency (HF)-heart rate variability (HRV) power (0.12–0.40 Hz); LF-HRV: low frequency (LF)-HRV power (0.04–0.12 Hz); HRDB: the HR response to deep breathing at 6 breaths per minute. Indicates that Pearson’s correlation is significant at P < 0.05. Indicates that Pearson’s correlation is significant at P < 0.001.