Cyclic sighing: a simple breath with a long exhale

Some of the oldest advice for a frightened body is also the simplest: breathe out slowly. Cyclic sighing is a structured version of that advice, and in 2023 it became one of the better-studied breathing exercises around. Here is what the research found, how to try it, and where the evidence stops.

What cyclic sighing is

A sigh is something your body already does without asking. Cyclic sighing turns it into a pattern you repeat on purpose:

1. Breathe in slowly through your nose until your lungs feel mostly full.
2. Take a second, shorter sip of air on top, to fill them completely.
3. Let a long, slow breath out through your mouth until you feel empty. The breath out should take longer than the breath in. If breathing out through your mouth feels odd, your nose is fine too.
4. Repeat for about five minutes.

The study

Researchers at Stanford published a remote, randomised controlled study in Cell Reports Medicine in 2023. They assigned 108 adults to one of four daily five-minute practices, done at home for about a month.^[1]

• Cyclic sighing, with the long breath out described above.
• Box breathing: breathing in, holding, breathing out and holding again, each for the same count.
• Cyclic hyperventilation with retention: rounds of deep breaths followed by a short hold with empty lungs.
• Mindfulness meditation: sitting quietly, breathing naturally and bringing attention back when it wanders. This was the comparison group.

Participants rated their mood and anxiety before and after each session, and wore a wristband that tracked breathing rate, heart rate and heart rate variability.

What it found

Anxiety and negative mood fell in every group, breathwork and meditation alike, with no clear difference between them. The differences showed up elsewhere. Using a statistical model, the researchers found that breathwork, and cyclic sighing in particular, lifted positive mood more than meditation did. Cyclic sighing was also the only single practice that slowed participants’ breathing rate more than meditation, a sign of lower physiological arousal. For cyclic sighing, the lift in mood grew larger the more days people had practised.^[1]

Two things did not change: heart rate and heart rate variability showed no significant shift in any group, and neither did the sleep measures the study tracked.

What it does not show

• It was small and early. 108 people split four ways leaves 21 to 33 per group. The study was designed to compare breathwork as a whole with meditation, not one breathing style with another. The authors call it exploratory, and it was registered only after it had run.
• Who took part. Most participants were Stanford students, recruited in the summer of 2020, and people with moderate or severe medical or psychiatric conditions were excluded. We don’t know how well the results apply to people with nightmare disorder, PTSD or insomnia.
• Remote and self-rated. Everyone practised alone at home, on average on about 18 to 20 of the 28 days, and mood was self-reported.
• One month. Follow-up lasted four weeks, so longer-term effects, and the smallest amount that helps, are unknown.
• Not a nightmare study. It was not designed to test breathing after waking from a bad dream.

Wider research points the same way, with the same caution. A 2023 meta-analysis of 12 randomised trials with 785 adults linked breathwork to lower stress, a small-to-medium effect, and urged care because most studies had a moderate risk of bias.^[2] A systematic review of slow breathing (under ten breaths a minute) in healthy people found links with higher heart rate variability, more relaxation and less anxiety, though only 15 studies met its criteria.^[3]

Why a long breath out may help

The mechanism is still being worked out. Your heart naturally speeds up a little as you breathe in and slows as you breathe out. Slow breathing strengthens this rhythm, which reflects the calming, parasympathetic side of the nervous system.^[3] Lingering on the breath out may lean into that slower half of the cycle. In the 2023 study, people whose breathing rate fell more also tended to gain more in positive mood: a modest correlation that fits the idea without proving it.^[1]

How to use it

• Practise in daylight first. Five minutes a day at a calm moment, so the pattern is familiar before you need it.
• Keep it gentle. The second breath in is a small top-up, not a gasp. If you feel light-headed, slow down or return to ordinary breathing.
• At 3 a.m., keep it short. After a nightmare, a minute or two of long breaths out may help your body catch up with the fact that you are safe. Then let your breathing settle by itself. If you are still wide awake after a while, the twenty-minute rule is the next step.
• Check first if you need to. The study excluded people with heart disease, pregnancy and several other conditions. If any apply to you, or breathing exercises tend to make you anxious, talk to your doctor before you start.

Breathing will not stop nightmares on its own. It may make the moments around them easier. For recurring nightmares, the method sleep medicine recommends is imagery rehearsal, and relaxation is listed as an option alongside it.^[4] For insomnia, relaxation is a suggested option too.^[5]

For a short version to keep, see the Atlas card on cyclic sighing. Baku’s Nightlight uses the same shape at night: a short swell in, a long fade out, felt as a pulse rather than read. See how it works at 3 a.m.