The physiological sigh: a fast, evidence-based way to calm down

The physiological sigh is a double inhale through the nose followed by a long, slow exhale through the mouth, and it is one of the quickest ways to bring your body down from a spike of stress. A 2023 Stanford study in Cell Reports Medicine found that practicing it for 5 minutes a day (called cyclic sighing) improved mood and slowed resting breathing more than mindfulness meditation did over a month. It costs nothing, works anywhere, and takes less time than reading your next Slack message.

What follows is what the study actually tested, why the breath works, and how a founder can use it without turning it into another performance metric.

What is a physiological sigh?

You have been doing it your whole life. A sigh is a deeper-than-normal breath that the brainstem triggers on its own, and it is not only about emotion. According to UCLA Health's summary of a 2016 Nature study by UCLA and Stanford researchers, "On average, a person sighs every five minutes, which translates into 12 sighs per hour."

The reason is mechanical. The lungs contain millions of tiny air sacs called alveoli, and some of them gradually collapse during ordinary shallow breathing. "When alveoli collapse, they compromise the ability of the lung to exchange oxygen and carbon dioxide," the release explains. "The only way to pop them open again is to sigh, which brings in twice the volume of a normal breath."

That same study, done in mice, located the circuit: roughly 200 neurons in the brainstem that release signaling molecules to a second set of about 200 neurons, which then drive the extra-large breath. Useful to know, with the standard caveat that brainstem wiring in mice is a strong clue about humans, not proof.

The deliberate version you may have heard about takes this built-in reflex and uses it on purpose. Two inhales to fully inflate the lungs, then an exhale that is longer than the inhales combined.

What did the Stanford 2023 study find?

The best human evidence comes from a randomized, remote study led by Melis Yilmaz Balban with David Spiegel and Andrew Huberman at Stanford, published in Cell Reports Medicine in January 2023.

Participants were healthy adults assigned to one of four 5-minute daily practices for 28 days:

• Cyclic sighing: a double inhale through the nose, then a slow, full exhale through the mouth, with emphasis on the exhale.
• Box breathing: equal-length inhale, hold, exhale and hold.
• Cyclic hyperventilation with retention: rapid, deep breathing followed by a breath hold, a pattern similar to some popular breathwork methods.
• Mindfulness meditation: attention on the breath without changing it.

Of 114 people invited, 108 were included in the analysis: 30 in cyclic sighing, 21 in box breathing, 33 in cyclic hyperventilation and 24 in mindfulness meditation. Every day they logged mood and anxiety, and a wearable tracked resting heart rate, heart rate variability and breathing rate.

Three findings matter.

Everyone got less anxious. Participants in both the meditation and breathwork groups "had a significant reduction in state anxiety," with no significant difference between them. If you are already meditating, that is good news. It works.

Breathwork lifted mood more. Daily positive affect rose in every breathwork group. The authors' summary is that "breathwork, especially the exhale-focused cyclic sighing, produces greater improvement in mood (p < 0.05) and reduction in respiratory rate (p < 0.05) compared with mindfulness meditation," as the Huberman Lab publication page at Stanford puts it. In the paper, "the cyclic sighing group had a significantly higher increase in positive affect than those in the mindfulness meditation group."

Breathing slowed at rest. The breathwork group had a significantly larger drop in resting respiratory rate than the meditation group, with cyclic sighing showing the most reduction. A slower resting breath is generally a sign of a calmer baseline state.

A note on reading that chart. The raw averages for the three breathing drills are close together, and the paper says the groups were too small to reliably rank them against each other. What stood out statistically, after the authors' modeling, was cyclic sighing against meditation. The paper's conclusion is measured: "Daily 5-min cyclic sighing has promise as an effective stress management exercise."

Why an exhale-focused breath calms you down

Your heart rate rises slightly on each inhale and falls on each exhale. The exhale is when the vagus nerve, the main brake of the parasympathetic nervous system, has the most influence on the heart. Stretch the exhale out, and you spend more of each breath with the brake engaged. This is the same beat-to-beat pattern that heart rate variability measures, and it is one reason chronic, fast, shallow breathing tends to travel with the always-on stress state described in what chronic stress does to a founder's body.

The double inhale does something slightly different. By fully reinflating the lungs, it sets up a large, slow exhale. When you are anxious, you often breathe fast and shallow from the upper chest. The sigh interrupts that pattern with a single, physical correction your body already knows.

Cyclic hyperventilation, by contrast, is an arousing technique. It deliberately speeds breathing and shifts blood chemistry before a breath hold. In the study it also improved mood, likely through a different route, but it is not a calming tool and carries real risks, including lightheadedness and fainting, especially near water or while driving. We do not give instructions for it here, and anyone with a heart condition, epilepsy, or who is pregnant should discuss it with a physician before trying it.

What the evidence says, and what it doesn't

Reasonably strong: The mechanics. Humans sigh spontaneously, and slow breathing with a long exhale shifts the heart toward parasympathetic control. These are well established.

Promising, but early: The Stanford study is randomized and measured physiology, not just self-report. It is also a single study. Its limitations, stated plainly by the authors:

• "The remote nature of the study limited the monitoring of how closely participants followed the instructions." Adherence averaged about 18 to 20 of the 28 days.
• It excluded people with moderate to severe psychiatric or medical conditions, so it says little about clinical anxiety or panic disorder.
• "The findings of this study are limited to 4 weeks with no additional follow up."
• "Sample size in each group was relatively small," limiting comparisons between breathing styles.

Broadly consistent: The National Center for Complementary and Integrative Health notes a 2017 review finding HRV biofeedback (which trains slow breathing) "helpful for reducing self-reported stress and anxiety," and a 2019 review with "preliminary evidence suggesting that diaphragmatic breathing exercises may help to reduce stress."

Not supported: Claims that one breath "resets your nervous system" permanently, or that breathing can treat an anxiety disorder on its own. NCCIH also notes that relaxation techniques are "generally considered safe for healthy people," but that "occasionally, people report negative experiences such as increased anxiety, intrusive thoughts, or fear of losing control."

If you experience panic attacks, chest pain, shortness of breath at rest, or anxiety that interferes with your work or sleep, see a physician or licensed clinician. A breathing drill is a tool, not a treatment plan.

How to do a physiological sigh

This is the pattern described in the Stanford paper, adapted for everyday use. Sit or stand comfortably.

1. Inhale through your nose until your lungs feel mostly full.
2. Take a second, shorter inhale through the nose to top them up. It will be smaller than the first. That is fine.
3. Exhale slowly through your mouth until your lungs feel empty. Make the exhale longer than both inhales combined.
4. Repeat. One to three sighs is often enough to feel a shift. For the daily practice the study used, continue for 5 minutes at a relaxed pace.

Keep it gentle. You are not trying to breathe hard; if you feel dizzy or tingly, slow down or stop and breathe normally.

How founders can use cyclic sighing this week

The advantage of this technique is that it fits in the gaps of a real day. Nobody in the room can tell you are doing it.

Before high-stakes moments. Three slow sighs in the elevator before a board meeting, or while your laptop connects to the investor call. The goal is to walk in with your breath low and slow, which makes it easier to think clearly. Our post on meditation for CEOs and decision-making covers why that state matters for judgment.

After a spike. A terse message from a co-founder, a customer escalation, a surprise number in the monthly close. Before you reply, do two or three sighs. You will still reply. You will just reply from a steadier place.

As a 5-minute daily practice. Pick a fixed slot, such as right after your first coffee or before you open email, and run 5 minutes of cyclic sighing. Try it for two weeks and note your mood and sleep. The Stanford participants kept a simple daily log, and you can too.

At night, gently. If you are lying awake at 1 a.m. replaying a conversation, a few slow sighs followed by normal, quiet breathing can help. See meditation for sleep for executives for the rest of that routine.

One caution for high performers: this is not a technique to max out. More, harder or faster is not better. The benefit comes from an easy, long exhale.

Where a single breath fits in a larger practice

The physiological sigh is a remarkably effective emergency brake. It is less good at changing the conditions that keep putting you in the situations where you need it. For that, founders usually need a steadier baseline: better sleep, fewer unexamined triggers, and a trained ability to notice activation early.

That is the work we do at Cinder, where private 1:1 coaching pairs fast tools like cyclic sighing with the slower meditation practice that makes you need them less. The Stanford data is a good reminder that both have a place: the breathwork lifted mood faster, and meditation reduced anxiety just as well.

Building a calmer default

If a five-minute breath can move your mood in a month, imagine what a practice designed around your calendar, your stressors and your goals can do over a year. We would be glad to help you build it.

Apply for private coaching

Sources

• Brief structured respiration practices enhance mood and reduce physiological arousal, Cell Reports Medicine (via PMC), 2023
• Brief structured respiration practices enhance mood and reduce physiological arousal (publication summary), Huberman Lab, Stanford University, 2023
• UCLA and Stanford researchers pinpoint origin of sighing reflex in the brain, UCLA Health, 2016
• Relaxation techniques: what you need to know, National Center for Complementary and Integrative Health, 2021