Time Domain Indicators
SDNN
- Standard deviation of all normal beat-to-beat intervals
- Reflects overall sympathetic-parasympathetic balance
-
100ms: Healthy state
- 50-100ms: Potential abnormality
- <50ms: Significant abnormality
RMSSD
- Root mean square of successive interval differences
- Reflects vagal nerve activity
- Sensitive to short-term measurements
- Suitable for wearable devices
pNN50
- Percentage of successive NN interval differences greater than 50ms
- Reflects vagal nerve regulation
- Typical value: 10-30%
Frequency Domain Indicators
High Frequency (HF)
- 0.15-0.40 Hz
- Respiratory sinus arrhythmia
- Parasympathetic activity
Low Frequency (LF)
- 0.04-0.15 Hz
- Combined sympathetic and parasympathetic regulation
- Related to blood pressure baroreflex
Very Low Frequency (VLF)
- <0.04 Hz
- Thermoregulation, hormone cycles
LF/HF Ratio
- Assesses autonomic nervous system balance
- Elevated: Sympathetic dominance
- Reduced: Parasympathetic dominance