Six breaths a minute: slow breathing and heart rate variability

Our heart does not beat like a metronome. When we breathe in it speeds up slightly; when we breathe out it slows down. This small variation, from one beat to the next, is called heart rate variability. In general, higher variability is linked with a more flexible nervous system that adapts more easily to stress.

Resonance breathing

The American psychologist Paul Lehrer and his colleagues have studied an interesting phenomenon for decades: when we breathe at a certain rhythm, usually about 5.5 to 6 breaths a minute in adults, the oscillations of the heartbeat become larger and match the breathing. This is called resonance breathing, because the systems of the heart and of blood pressure seem to "resonate" at this rhythm.

In practice this means about 10 seconds per cycle: about 4–5 seconds to breathe in and 5–6 seconds to breathe out.

What studies say

Studies of heart rate variability biofeedback, in which people learn to breathe at this rhythm while watching their heartbeat on a screen, have shown improvements in stress, anxiety and some other symptoms. A 2017 review by Goessl, Curtiss and Hofmann found a substantial reduction in reported stress and anxiety. But many studies are small, and it is not always clear how much of the effect comes from the exact rhythm and how much from the general calm that slow breathing brings.

Breathing is the only part of the automatic nervous system we can steer at will. That makes it a small door to calm.

How to try it

1. Sit comfortably, with a straight back and relaxed shoulders.
2. Breathe in through the nose for about 4–5 seconds, letting the belly expand.
3. Breathe out slowly for about 5–6 seconds, through the nose or through slightly parted lips.
4. Continue for 5 minutes. You can use an app or a video with a circle that grows and shrinks.
5. Do not force it. If you feel dizzy or short of air, return to normal breathing. For some people the most comfortable rhythm is slightly faster.

This exercise complements the cyclic sighing we wrote about earlier. Both are simple, safe for most people and can be done anywhere. People with heart or lung conditions should talk to their doctor first.