Table 2: Descriptions of the HRV measures analyzed [14] and their trend under stress [15].

Domain Measure Description Features Trend Under Stress
Time-domain AVNN Average of NN intervals (ms)
RMSSD Root mean square of differences of successive NN intervals (ms)
pNN20 NN variations above 20 ms (%)
Frequency-domain LF/HF Ratio of Low Frequency and High Frequency power bands.