If you have ever let out a long sigh after a stressful moment, you already know something your body seems to understand on its own. Breathing out slowly often feels like letting go.

There is some interesting science behind that feeling. This article walks through what researchers know about the out-breath, slow breathing and the nervous system, and just as importantly, where the evidence is still thin.

Your heart rate changes with every breath

Put two fingers on your wrist and breathe slowly. If you pay close attention, you may notice your pulse speeds up slightly as you breathe in and slows slightly as you breathe out.

This is called respiratory sinus arrhythmia, or RSA. Despite the slightly alarming name, it is normal and healthy. As Russo and colleagues describe in their review of slow breathing, heart rate tends to rise during inhalation and fall during exhalation, so the gaps between heartbeats shorten and lengthen in time with your breath. RSA is often used as a rough indicator of how active the vagus nerve is in regulating the heart, although other body systems play a part in it too.

In simple terms: the in-breath tends to nudge your heart rate up a little, and the out-breath tends to let it ease down.

The two branches of your nervous system

Your autonomic nervous system runs things you do not consciously control, like heart rate and digestion. It has two main branches:

  • The sympathetic branch, often called "fight or flight", gets you ready for action.
  • The parasympathetic branch, sometimes called "rest and digest", helps you settle and recover.

The vagus nerve is a major pathway for the parasympathetic side, and it is the one that slows the heart. When you are anxious, the sympathetic side tends to dominate. Your heart beats faster and your breathing speeds up.

You cannot directly tell your heart to slow down. But you can change how you breathe, and breathing is linked to both branches.

Why the exhale gets attention

If the heart tends to slow during the out-breath, it makes intuitive sense that spending a bit more of each breath exhaling might tilt things toward the calmer side.

There is some research supporting this. In a small study published in Scientific Reports, Magnon, Dutheil and Vallet (2021) asked younger and older adults to do one session of slow breathing with a longer exhale than inhale. The session increased a heart rate variability measure linked to vagal activity and reduced self-reported state anxiety in both age groups. The effect on the vagal measure was stronger in older adults.

A larger study at Stanford by Balban and colleagues (2023) compared three five-minute daily breathing practices with mindfulness meditation over one month. One practice was "cyclic sighing", which emphasises a long, slow exhale. All the breathing groups improved, and cyclic sighing produced a greater improvement in positive mood and a greater drop in resting breathing rate than the mindfulness group.

These are encouraging findings. They are also specific: healthy volunteers, particular protocols, limited sample sizes. They suggest that an exhale-focused rhythm may help many people feel calmer. They do not show that a longer exhale will stop a panic attack.

Slow breathing and heart rate variability

Heart rate variability (HRV) is the natural variation in time between heartbeats. Higher vagally mediated HRV is generally associated with a body that can shift flexibly between activation and rest.

Slow breathing is one of the most reliable ways to influence HRV in the short term. A large systematic review and meta-analysis by Laborde and colleagues (2022), covering 223 studies, found that voluntary slow breathing increased vagally mediated HRV during the practice, right after a single session, and after multi-session programmes. The authors suggest slow breathing could be a low-cost technique for prevention and as an add-on to other treatment, with few expected side effects.

The "6 breaths per minute" idea

You may have seen the number six breaths per minute, which is roughly a 10-second breath cycle. Research on HRV biofeedback, summarised by Lehrer and Gevirtz (2014), describes a "resonance frequency" for most adults at around this pace. At this rhythm, heart rate swings with the breath become especially large, which appears to exercise the reflexes that help regulate blood pressure.

An earlier systematic review by Zaccaro and colleagues (2018) looked at slow breathing under 10 breaths per minute in healthy people. It linked slow breathing with increased HRV and RSA, as well as reports of more comfort and relaxation and fewer feelings of anxiety and arousal. The review included only 15 studies, which is a reminder that this field is still young.

What the evidence does not show

It is easy to oversell breathing. Here is a more honest picture:

  • Most studies involve healthy adults, not people in the middle of a panic attack. Russo and colleagues (2017), in their review of slow breathing physiology, conclude there is "a dire need for further research".
  • Short-term changes are not long-term outcomes. An HRV increase during a five-minute session does not by itself mean lasting changes in anxiety.
  • Studies use different protocols. Breath ratios, rates and session lengths vary, so it is hard to say one exact rhythm is best.
  • Feeling better is personal. Some people find slow breathing soothing straight away. Others find that focusing on their breath makes them more aware of uncomfortable sensations at first.

What the research does support is a reasonable, low-risk idea. Slower breathing, with a comfortable exhale that is a little longer than the inhale, can support your body's natural tendency to settle.

Putting it into practice

You do not need a lab to try this. A simple version:

  1. Breathe in gently through your nose for a count of about 3 or 4.
  2. Breathe out slowly for a count of about 5 or 6.
  3. Keep it comfortable. If you feel lightheaded, shorten the counts or breathe normally for a moment.
  4. Continue for a few minutes.

If you are already anxious, start at a quicker pace that matches your breathing, then slow down bit by bit. Our step-by-step guide on how to breathe during a panic attack goes into this in more detail.

This is the approach behind Don't Panic Daisy. The flower guides a gentle inhale and a slightly longer exhale, starts at a quicker pace and gradually slows down, so you are not asked to leap straight to a slow rhythm. You can adjust the pace whenever you need to. If you are curious how this compares with other patterns, see box breathing vs 4-7-8 vs extended exhale.

The short version

  • Your heart rate tends to rise a little as you breathe in and fall a little as you breathe out.
  • Slow breathing reliably increases heart rate variability measures linked to vagal activity.
  • Some studies suggest exhale-focused breathing may improve mood and reduce anxiety in the moment.
  • The research is promising, but it is mostly short-term and in healthy volunteers.

A longer exhale is a small, gentle tool. It costs nothing, you can use it anywhere, and many people find it helps.

Sources

This article is general information, not medical advice. Don't Panic Daisy is not a medical device and does not replace professional care. If you are in crisis or think you might harm yourself, contact your local emergency services or a crisis line right away.