HRV (Heart Rate Variability)

Heart Rate Variability (HRV) measures the variation in time intervals between consecutive heartbeats, known as R-R intervals or inter-beat intervals (IBI). Rather than beating at a perfectly regular rhythm, a healthy heart exhibits subtle variations in timing that reflect the dynamic interplay between the sympathetic and parasympathetic branches of the autonomic nervous system.

Higher HRV generally indicates better cardiovascular fitness, greater stress resilience, and more robust autonomic regulation. Lower HRV has been associated with increased risk of cardiovascular disease, chronic stress, anxiety, depression, and higher all-cause mortality. Common HRV metrics include SDNN (overall variability), RMSSD (parasympathetic activity), and various frequency-domain measures.

HRV can be measured contactlessly using rPPG technology by extracting precise inter-beat intervals from facial video. While short-term rPPG-based HRV measurements are best suited for trend monitoring and relative comparisons rather than clinical diagnosis, they provide valuable data for fitness assessment, stress monitoring, recovery tracking, and wellness program evaluation.