Long exhalation and the vagus nerve: what’s known and what’s hype

Author: Raymond Hackland · Last reviewed: 18 October 2026 · Reading time: about 7 minutes

In short

• What this is: The vagus nerve links your brain with your heart, lungs and gut. With every breath out, your heart slows down a little, partly through this nerve. That is why long exhalations are often called a way to “activate your vagus nerve”.
• What the evidence says: Slow breathing reliably increases the part of heart rate variability (HRV) linked to the vagus nerve. Whether making the out-breath longer than the in-breath adds anything is early evidence with mixed results. Popular claims about “resetting” the vagus nerve, and the polyvagal theory behind much of this language, are speculative and strongly disputed.
• What it means for your practice: A slow, unhurried out-breath is a simple, safe way to change how your heart and breath work together. You don’t need a gadget, a theory or a “vagus hack” for that, and it is not a treatment for any condition.

Background: what the vagus nerve is

The vagus nerve is the tenth cranial nerve. It runs from the brainstem through the neck and chest down into the abdomen. A detail that rarely makes it into wellness posts: about 80 to 90 percent of its fibres carry information from the body to the brain, and only 10 to 20 percent carry signals from the brain to the organs [15]. One of those outgoing jobs is slowing the heart.

What science says

Label for this section: Early evidence (the general effect of slow breathing on HRV is well studied, see below).

Your heart slows on the out-breath. When you breathe in, your heart speeds up slightly; when you breathe out, it slows down again. This rhythm, called respiratory sinus arrhythmia (RSA), depends largely on the vagus nerve and is one of the main ingredients of HRV [4, 9]. Researchers use certain HRV measures, such as RMSSD and high-frequency power, as indirect markers of vagal influence on the heart, called vagally mediated HRV [8].

Slow breathing: well documented. A 2022 meta-analysis of 223 studies found that vagally mediated HRV rose during slow breathing, straight after a single session, and after programmes of several sessions [1]. We explain the physiology of breathing at about six breaths a minute in our article Slow breathing and heart rate variability: what actually happens in your body.

Does a longer out-breath add anything? Mixed results. A handful of small lab studies have compared different ratios of in-breath to out-breath:

• In a Belgian study with 30 participants, breathing with a long exhalation (about 30 percent in, 70 percent out) produced more high-frequency HRV than the reverse pattern, but only at six breaths a minute, not at twelve. Participants also felt more relaxed with the long exhalation [2].
• In a German study with 64 athletes breathing at six breaths a minute, RMSSD was higher when the out-breath was slightly longer than the in-breath than with equal or longer in-breaths. Short pauses between breaths made no difference [3].
• Other results point the other way or are mixed. A 2017 review reported a tendency for HRV to increase most with equal in- and out-breaths during slow breathing [4]. In a French study of younger and older adults, slow breathing with a long exhalation raised high-frequency power, but RMSSD did not increase [5]. A Belgian study found that equal and exhale-weighted breathing both raised HRV compared with watching a film [6]. In a 2026 trial with 66 people, a prolonged-exhalation exercise before a stress test reduced the rise in heart rate and self-reported anxiety compared with normal breathing, but HRV did not differ between the groups [7].

Taken together: slowing down matters most. A longer out-breath may add a small extra effect on some HRV measures, but the studies are few, small and use different measures. That is why this part carries the Early evidence label.

What HRV can and cannot tell you. HRV is an indirect marker, not a direct reading of “vagal tone”. Respiration itself changes RSA, so when you change how you breathe, the measurement changes partly because of the breathing [8, 9]. Physiologists have long warned that RSA and cardiac vagal tone can come apart under certain conditions [9]. HRV is also a measurement, not a health outcome.

Where popular claims go beyond the evidence

Label for this section: Speculative.

• “A long exhale activates (or resets) your vagus nerve.” The vagus nerve is never switched off. Breathing out shifts the vagal influence on the heart from moment to moment; that is normal physiology, not a reset. There is no measurable “reset” state.
• “Get into your ventral vagal state.” This language comes from the polyvagal theory, proposed by Stephen Porges. It holds that mammals have two vagal circuits: an evolutionarily newer “ventral” one linked to social engagement and an older “dorsal” one linked to shutdown, with RSA as the window onto the newer circuit [10, 13]. Many physiologists reject the theory’s core premises. As early as 2007, Grossman and Taylor argued that its account of the evolution of vagal heart control is inaccurate, and that heart-rate rhythms linked to breathing are found in fish and other non-mammals too [9, 12]. In 2023, Grossman argued that each of the theory’s five basic premises is untenable or highly implausible, and that treating RSA as if it were vagal tone confuses an approximate index with the thing itself [11]. In 2026, he and 38 co-authors working in autonomic physiology and vertebrate evolution concluded that the theory is “untenable” [12]. Porges replied that the critique misrepresents the theory as he formulates it [14]. The debate continues, but the neuroanatomy behind “ventral vagal” talk is not established science. The everyday insight that feeling safe helps us relax does not depend on the theory [12].
• “Your watch measures your vagal tone.” It estimates HRV, which reflects vagal influence on the heart only indirectly and is affected by breathing, movement and measurement method [8, 9].
• “Ear clips and gadgets stimulate your vagus nerve better than breathing.” Transcutaneous auricular vagus nerve stimulation (taVNS) sends a weak electrical current through the skin of the outer ear. It is being studied in clinical research, which is outside the scope of this article. As a way to raise vagally mediated HRV, it has not held up: a 2021 meta-analysis of 16 sham-controlled studies in healthy people found strong evidence that acute taVNS does not change vagally mediated HRV compared with sham stimulation [16]. Researchers have proposed combining taVNS with slow breathing [17], but when 22 people breathed at six breaths a minute with stimulation timed to each out-breath, taVNS added nothing to HRV compared with sham [18]. Slow breathing itself, by contrast, consistently changes HRV [1].
• “Vagus hacks fix anxiety, inflammation or digestion.” None of the studies cited here tested such outcomes in everyday self-practice. Breathing exercises are not a substitute for medical care.

How this relates to the Six Healing Sounds, Qigong and neigong

Label for this section: Early evidence (slow, exhale-weighted breathing and HRV) · Tradition only (Qigong and neigong concepts) · Speculative (vagus-nerve and polyvagal language applied to Qigong).

Each of the six sounds is voiced on a long, unhurried out-breath, followed by a quiet in-breath through the nose. So, in shape, the practice already leans towards the exhale-weighted, slow breathing described above. Whether your own practice reaches that pace depends on you, and none of the studies cited here tested Liu Zi Jue itself. Voicing a sound is also one natural way to lengthen and steady the out-breath; humming is another, and we look at what happens in the nose when you hum in Humming and nitric oxide in the nose.

You may hear Qigong or neigong described as “vagus nerve training” or as a way into a “ventral vagal state”. That is modern vocabulary, borrowed from popular physiology and from the polyvagal theory, which is strongly disputed [11, 12]. Qigong and neigong describe breath, attention and qi in their own traditional terms, and those are not measurements of the vagus nerve. What can honestly be said is narrower: slow breathing changes vagally mediated HRV [1], and long, soft out-breaths are part of these practices.

Resonance Heritage Qi is a personal, music-assisted practice inspired by Liu Zi Jue: connected to it, not a replacement for the traditional form or for study with a teacher of that tradition. If you enjoy long, soft exhalations, the sounds give you a gentle, structured way to practise them, without needing a device or a theory about your nervous system.

Try it gently (optional)

1. Sit upright and comfortably. Let your shoulders drop.
2. Breathe in quietly through your nose for about four seconds.
3. Breathe out softly for about six seconds, through the nose or on a whispered “hhh” through the mouth.
4. Continue for three to five minutes. If counting makes you tense, simply let the out-breath be a little longer and slower than usual.
5. Finish with a few natural breaths and notice how you feel.

Never force your breath or squeeze out the last bit of air. If you feel dizzy, lightheaded or short of breath, stop and breathe normally.

Sources

1. Laborde S, Allen MS, Borges U, Dosseville F, Hosang TJ, Iskra M, Mosley E, Salvotti C, Spolverato L, Zammit N, Javelle F, 2022. Effects of voluntary slow breathing on heart rate and heart rate variability: a systematic review and a meta-analysis. Neuroscience & Biobehavioral Reviews 138:104711. https://doi.org/10.1016/j.neubiorev.2022.104711
2. Van Diest I, Verstappen K, Aubert AE, Widjaja D, Vansteenwegen D, Vlemincx E, 2014. Inhalation/exhalation ratio modulates the effect of slow breathing on heart rate variability and relaxation. Applied Psychophysiology and Biofeedback 39(3–4):171–180. https://doi.org/10.1007/s10484-014-9253-x
3. Laborde S, Iskra M, Zammit N, Borges U, You M, Sevoz-Couche C, Dosseville F, 2021. Slow-paced breathing: influence of inhalation/exhalation ratio and of respiratory pauses on cardiac vagal activity. Sustainability 13(14):7775. https://doi.org/10.3390/su13147775
4. Russo MA, Santarelli DM, O’Rourke D, 2017. The physiological effects of slow breathing in the healthy human. Breathe 13(4):298–309. https://doi.org/10.1183/20734735.009817
5. Magnon V, Dutheil F, Vallet GT, 2021. Benefits from one session of deep and slow breathing on vagal tone and anxiety in young and older adults. Scientific Reports 11:19267. https://doi.org/10.1038/s41598-021-98736-9
6. De Couck M, Caers R, Musch L, Fliegauf J, Giangreco A, Gidron Y, 2019. How breathing can help you make better decisions: two studies on the effects of breathing patterns on heart rate variability and decision-making in business cases. International Journal of Psychophysiology 139:1–9. https://doi.org/10.1016/j.ijpsycho.2019.02.011
7. McAllister MJ, Martaindale MH, Sutton N, Andersen JP, 2026. Box breathing and prolonged exhalation reduces markers of physiological stress reactivity in response to a virtual Trier social stress test. Comprehensive Psychoneuroendocrinology 27:100360. https://doi.org/10.1016/j.cpnec.2026.100360
8. Laborde S, Mosley E, Thayer JF, 2017. Heart rate variability and cardiac vagal tone in psychophysiological research: recommendations for experiment planning, data analysis, and data reporting. Frontiers in Psychology 8:213. https://doi.org/10.3389/fpsyg.2017.00213
9. Grossman P, Taylor EW, 2007. Toward understanding respiratory sinus arrhythmia: relations to cardiac vagal tone, evolution and biobehavioral functions. Biological Psychology 74(2):263–285. https://doi.org/10.1016/j.biopsycho.2005.11.014
10. Porges SW, 2007. The polyvagal perspective. Biological Psychology 74(2):116–143. https://doi.org/10.1016/j.biopsycho.2006.06.009
11. Grossman P, 2023. Fundamental challenges and likely refutations of the five basic premises of the polyvagal theory. Biological Psychology 180:108589. https://doi.org/10.1016/j.biopsycho.2023.108589
12. Grossman P, Ackland GL, Allen AM, Berntson GG, et al. (39 authors), 2026. Why the polyvagal theory is untenable: an international expert evaluation of the polyvagal theory and commentary upon Porges, S.W. (2025). Clinical Neuropsychiatry 23(1):100–112. https://doi.org/10.36131/cnfioritieditore20260110
13. Porges SW, 2025. Polyvagal theory: current status, clinical applications, and future directions. Clinical Neuropsychiatry 22(3):169–184. https://doi.org/10.36131/cnfioritieditore20250301
14. Porges SW, 2026. When a critique becomes untenable: a scholarly response to Grossman et al.’s evaluation of polyvagal theory. Clinical Neuropsychiatry 23(1):113–128. https://doi.org/10.36131/cnfioritieditore20260111
15. Breit S, Kupferberg A, Rogler G, Hasler G, 2018. Vagus nerve as modulator of the brain–gut axis in psychiatric and inflammatory disorders. Frontiers in Psychiatry 9:44. https://doi.org/10.3389/fpsyt.2018.00044
16. Wolf V, Kühnel A, Teckentrup V, Koenig J, Kroemer NB, 2021. Does transcutaneous auricular vagus nerve stimulation affect vagally mediated heart rate variability? A living and interactive Bayesian meta-analysis. Psychophysiology 58(11):e13933. https://doi.org/10.1111/psyp.13933
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18. Szulczewski MT, D’Agostini M, Van Diest I, 2023. Expiratory-gated transcutaneous auricular vagus nerve stimulation (taVNS) does not further augment heart rate variability during slow breathing at 0.1 Hz. Applied Psychophysiology and Biofeedback 48(3):323–333. https://doi.org/10.1007/s10484-023-09584-4

Source quality note: [1] is a large meta-analysis (223 studies) of slow breathing in general. The studies on in-breath/out-breath ratio ([2], [3], [5], [6], [7]) are small (30 to 66 participants), mostly single-session lab experiments, and use different HRV measures; [4] is a narrative review. [8] and [9] are methodological reviews. On polyvagal theory, [11] and [12] are critiques and [10], [13] and [14] are by the theory’s author; this is an active scientific dispute, and both sides are cited. [16] pools 16 small sham-controlled taVNS studies in healthy people; [17] is an explicitly speculative non-systematic review; [18] is a single small crossover study. None of these sources tested Liu Zi Jue.