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Table 1 Description of heart rate variability (HRV) stress indices

From: Self-assessment of surgical ward crisis management using video replay augmented with stress biofeedback

Heart rate variability
(HRV) stress indices
Description Value
Average heart rate (HR) Average absolute heart rate in time window Higher: higher stress
Lower: lower stress
Sample entropy (SE) Complexity of the HRV: assumes a complexity loss under constraints (e.g. stress) Higher: lower stress
Lower: higher stress
Low frequency/high frequency ratio (LF/HF) Balance between sympathetic and parasympathetic nervous systems.
LF: associated with sympathetic nervous system, HF: associated with parasympathetic nervous system
Higher: higher stress
Lower: lower stress
Standard deviation of RR Intervals (SDRR) Variation of RR intervals around a mean value Higher: lower stress
Lower: higher stress
Root mean squared of successive differences (RMSSD) Absolute variation of RR intervals Higher: lower stress
Lower: higher stress
Percentage of RR interval pairs with difference > 50 ms (PRR50) Compares each pair of adjacent RR intervals and considers the difference between them; if it is larger than 50 ms a counter is increased by one. The ratio of the counter and the number of RR intervals in one time window is pRR50 Higher: lower stress
Lower: higher stress