Supplementary Material for: Heart Rate Variability for Evaluating Psychological Stress Changes in Healthy Adults: A Scoping Review

The utility of heart rate variability (HRV) for characterizing psychological stress is primarily impacted by methodological considerations such as study populations, experienced versus induced stress, and method of stress assessment. Here, we review studies on the associations between HRV and psychological stress, examining the nature of stress, ways stress was assessed, and HRV metrics used. The review was performed according to the PRISMA guidelines on select databases. Studies that examined the HRV-stress relationship via repeated measurements and validated psychometric instruments were included (<i>n</i> = 15). Participant numbers and ages ranged between 10 and 403 subjects and 18 and 60 years, respectively. Both experimental (<i>n</i> = 9) and real-life stress (<i>n</i> = 6) have been explored. While RMSSD was the most reported HRV metric (<i>n</i> = 10) significantly associated with stress, other metrics, including LF/HF (<i>n</i> = 7) and HF power (<i>n</i> = 6) were also reported. Various linear and nonlinear HRV metrics have been utilized, with nonlinear metrics used less often. The most frequently used psychometric instrument was the State-Trait Anxiety Inventory (<i>n</i> = 10), though various other instruments have been reported. In conclusion, HRV is a valid measure of the psychological stress response. Standard stress induction and assessment protocols combined with validated HRV measures in different domains will improve the validity of findings.