HRV (Heart Rate Variability)

Topic Infobox
Linked pages on this wiki	Tools (10), Projects (57), People (2)

Definition

HRV is defined as the changes in the time interval between successive heartbeats.

Common Uses

People are interested in HRV primarily because it is regulated by the autonomic nervous system (ANS), which also regulates heart rate and blood pressure. This means that HRV can potentially provide useful information about questions pertaining to our overall nervous system, including information about stress, rest, recovery, and immune response. The two components of the ANS, the sympathetic and the parasympathetic nervous system, both influence HRV.

Measurement Approach

Since HRV measures the change over time of the interval between heart beats, there are many options available for producing a value relevant to a specific question. The heartbeat itself is not instantaneous, of course, but for the purpose of HRV measurement, the time is measured between ECG peaks known as R-R intervals. However, many people have irregular heartbeats, and so HRV is better calculated using NN intervals; that is, the time between ECG peaks when the heart is in a normal rhythm. Four common ways of determining HRV values, with their commonly used associations, are:

• Standard Deviation of NN-Interval (SDNN)
  • Risk of mortality in cardiac patients
• Standard Deviation of 5-minute averages of NN-Interval (SDANN)
  • Predominant circadian rhythm
• The Root Mean Square of Successive NN-Interval Differences (rMSSD)
  • Vagal modulation of heart rate.
• The Percentage of NN-Intervals that Are Greater than 50ms Different than Prior NN-Interval (pNN50)

Any instrument that reliably provides continuous heart rate data can be used as a basis for calculating HRV. Of course not all instruments are equally reliable and convenient, but the suitability for HRV is determined both by the instrument quality and by the situation of measurement. Less precise instruments can be used when the measurement context is well controlled.

Tools

• Apple Watch
• Fitbit
• Oura Ring
• Garmin
• Polar
• HRV4Training

Company	Model or Series	Release Date	Metrics	Sensor	In Production?
Apple	Watch
Fitbit	Sense
Fitbit	Versa			Optical heart rate monitor
Fitbit	Charge

Projects

• Paul LaFontaine: “We never fight on Wednesdays”

People

• Andrew Ahn
• Marco Altini