Biofeedback

What Is Heart Rate Variability, and Why Does It Matter?

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Heart rate variability, or HRV, is the variation in the time between one heartbeat and the next. It reflects the push and pull between the two branches of the nervous system that speed the heart up and slow it down. Reduced HRV has been linked to several health outcomes, and HRV can be trained with slow breathing, but a single number from a device is not a diagnosis.

What exactly is being measured?

The gaps between beats. The Wikipedia article on heart rate variability defines HRV as the variation in the time interval between heartbeats, measured from one beat-to-beat interval to the next. A steady pulse of 60 beats a minute does not mean the beats arrive exactly one second apart.

Beats can be detected in several ways. The article describes the electrocardiogram (ECG) as the gold standard because it reflects the heart’s electrical activity directly; another method uses the pulse wave picked up by a photoplethysmograph. The article also stresses that errors in the recording must be handled carefully before any analysis.

What does HRV reflect?

The balance of the autonomic nervous system. According to the same article, the parasympathetic branch works to slow the heart and the sympathetic branch works to speed it up, and decreased parasympathetic activity or increased sympathetic activity results in reduced HRV.

Part of the variation follows your breathing. The article describes respiratory sinus arrhythmia, a pattern in which heart rate rises as you breathe in and falls as you breathe out, carried by the vagus nerve.

Why does it matter for health?

Because lower HRV appears alongside a number of conditions. The article reports that reduced HRV has been shown to predict mortality after a heart attack, although other researchers found that the same information is fully contained in the average heart rate. It lists other conditions associated with modified, usually lower, HRV, including congestive heart failure and diabetic nerve damage.

An association is not a cause, and a low reading on its own tells you nothing certain about your heart. That judgment belongs to a clinician with the full picture.

Can you change your HRV?

Researchers have developed a way to train it. Paul Lehrer and Richard Gevirtz describe heart rate variability biofeedback as feeding back heart rate beat by beat while the person breathes slowly, trying to make the rise and fall of heart rate with each breath as large as possible.

They report that these swings in heart rate are largest at a breathing rate that differs from person to person but sits around six breaths per minute, with a later average from their research of about 5.5 breaths per minute, or roughly 11 seconds per breath. The 2019 evidence map of biofeedback brought together 16 systematic reviews on conditions such as headache, incontinence and fibromyalgia. None of them was a review of HRV biofeedback, so the map does not answer how well this method works for particular conditions.

How to read your own number

Compare yourself with yourself. Measure under the same conditions each time, such as on waking, and look at the trend over weeks rather than a single day. If your device flags something that worries you, or if you have symptoms such as chest pain, palpitations or breathlessness, take it to a doctor rather than to the app.

This article is general information, not medical or psychological advice; talk with a licensed clinician about your own situation.

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