Table 1.

Summary of the normal values of HRV.

Component	Outcome parameter	Clinical indication
Very low frequency (VLF)	Frequency (0.0033–0.04 Hz)	Indicator of overall activity of various slow sympathetic activities
Low frequency (LF)	Frequency (0.04–0.15 Hz)	Indicator of sympathetic activities with parasympathetic influence when the respiration rate is lower than 7 per minute
High frequency (HF)	Frequency (0.15–0.4 Hz)	Indicator of parasympathetic activities
LF/HF ratio	1.5–2.0	Indicator of sympathetic activities; a higher number means increased sympathetic activities or reduced parasympathetic activities
sNormalized LF and HF (LF norm, HF norm)	Frequency (Hz)	The monotonic nonlinear transformation of LF/HF ratio. The LF/HF ratio, LF norm, and HF norm indicate the same aspects of sympathovagal balance of autonomic nervous system