HRV

Full article coming soon. Below is a short overview that will be replaced.

What it is

Heart rate variability is the variation in time between successive heartbeats. A healthy heart does not beat at a perfectly steady rhythm, and the small changes from beat to beat carry information about how the nervous system is regulating the body.

How it is measured

Heart rate variability is derived from the intervals between beats, recorded with an ECG or a chest strap, or estimated from a wrist or finger optical sensor. The 1996 task force standard from the European Society of Cardiology and the North American Society of Pacing and Electrophysiology defines the common measures. RMSSD and SDNN are two widely used time-domain measures, and RMSSD is the usual short-term index of vagally mediated variability.

Breathing

Heart rate rises on the inhale and falls on the exhale, an effect called respiratory sinus arrhythmia. Slow breathing near six breaths a minute is commonly used in HRV biofeedback because it produces large oscillations in heart rate.

Reading the number

HRV is context dependent. It differs between people, changes with age, posture, sleep and stress, and a single reading means little. Trends measured the same way under the same conditions are more informative.