Slow exhalations: are they a meditative breathing upgrade?

Technically, this post is a re-run. But it is new for most of you … because it was a members-only post when I first published it in April 2022. This is the first time I have taken down the paywall on a premium post since I started the membership program in 2022. (It does still have a members-only audio version.)

Taking a little extra time with breathing out is thought to be even more relaxing and healthful than just taking deep breaths with roughly equal inhalations and exhalations.

Is it really, though?

I ran into this question blogging about Phil Greenfield’s thoughts on “treating anxiety physiologically.” I was on the verge of adding some value to Phil’s suggestions by advising readers to “extend your exhalations,” a meditation and breathing-exercise refinement I have practiced myself for many years — it’s practically a reflex at this point — and I have long endorsed it in my own article about anxiety.

If it’s worth breathing slowly and deeply, it’s worth doing it right. Amiright? But as I attempted to explain the rationale for it, I hit some snags. I went digging for more evidence … and it didn’t go super well.

Just once, I’d like to check my assumptions and just have them confirmed! But assumptions, by nature, are usually wrong, and conventional wisdom is rarely wise. So here I am, consuming yet more humble pie — an occupational hazard. (My entire writing career has just been a series of falls down rabbit holes every time I ask “is it really, though?”)

I was wrong about slow exhalations, but at least I was wrong in an interesting way. This post is all about what I learned.

The record I’m correcting

For posterity and context, here’s exactly what I had to say about this topic in my anxiety article (now long gone):

“Exhalation is literally more relaxing than inhalation,” I wrote (abusing the term literally a little). And that claim was substantiated solely by a single expert quote. It’s not really an “extraordinary claim,” and so it doesn’t need extraordinary evidence … but it does need some evidence.

What I had written wasn’t entirely wrong — exhalation really does slow some physiology down — but it’s so much more complicated than that.

What does this have to do with pain?

Most kinds of chronic pain have no good short-term treatment options. And so the next best thing for many patients is to cast a wide net and try to reduce vulnerability to pain over the long-term by improving every possible aspect of health and fitness. While satisfaction from this approach is not guaranteed or quick, it is a valuable investment in health regardless.

And so all kinds of health optimizations are potentially important for managing stubborn pain. But of course many of these things are time-wasting nonsense, and we also need to pick our battles — pain patients more than most have no energy to spare. And that’s why I critically evaluate claims like “exhalation is more relaxing that inhalation.” And because anything to do with yoga and meditation is so popular.

Heart rate and breathing

I can’t believe I paid for this cheezy stock photo of a meditating business dude.

Why does anyone believe that slow exhalations might be important? Where does this idea come from? Believe it or not, it’s all about heart rate. Starting with what we know for sure…

Hearts really do speed up slightly when we breathe in, and slow down a bit as we let it out. This curious pace change is the “respiratory sinus arrhythmia” (RSA): a slight inconsistency in our heart rhythm tied to respiration. Just a little body oddity.1 (All the footnotes in this post are just boring citations, rather than my usual elaborations and digressions — just worked out that way for some reasons.)

Every animal with a spine does this, and we don’t really know why.2 But the assumption is that the slowing of the heart rate during exhalation is a Good Thing. It must be, since it’s just how vertebrates do biological business. Like sleeping or sneezing or pandiculation, we reckon it must be useful or evolution would have beaten it out of us long ago.

Heart rate variability

You can quantify RSA by measuring the difference between the faster and slower rates, known as heart rate variability (HRV). My average HRV is usually 35 milliseconds: that is, the gap between my heartbeats is 34ms longer during exhalation than inhalation. This average has been quite consistent over long periods.

Ahhh. 35ms longer is so luxurious. It’s nice to take time for things, you know?

We know that a high average HRV is loosely linked to good health (although the details are a real can of worms), and we know (more notably for this topic) that stress stifles the RSA and pushes HRV down.3 (And yet I’ve had fairly obvious increases in HRV during some really stressful weeks. Go figure. But never mind that.)

And therefore: Less HRV bad! More HRV good! And that clinches the deal: exhalation must be healthifying, because it slows our heart rate down in everyone … and more so in happy, healthy humans. Therefore, take your time while you exhale.

And that is more than good enough for most people. Very science! So biology!

HRV as a new health metric

The value of HRV has gone mainstream, a popular new way to quantify our health. It’s obviously not as famous or important as blood pressure, but it is supposedly worth knowing about. It is being actively “marketed” as a rough measure of resilience and vitality of the organism.

If you have an Apple Watch, for instance, that gadget will measure and chart your HRV for you. (Notably without making any claims about what it’s actually good for. Imagine if they provided this text as the “fine print” for that feature!) My Apple Watch constantly monitors my heart rate and calculates my HRV, and so I can be amused by a data visualization like this:

For whatever it’s worth, my average HRV in February 2021 was 34 milliseconds… with happy spikes to over 50, and sad dips into the low 20s. In simplistic theory, the lows should line up with stresses. Do they? I am a journaler, so I know the dates of my worst days, and those days “should” have HRV lulls… but they do not. I don’t even see a correlation with extremes of sleep loss (which I have semi-regularly), and that seems like a really definite source of physiological stress. Checking again in 2023, my average is still 34ms, and lack of correlation with stressors continues.

Can we control HRV with breathing and does it matter?

We know that…

• RSA is a thing bodies do
• we can roughly measure it with HRV
• it’s probably relevant to overall health and suppressed by stress

But abandon all hope of confidence about anything beyond this point. Unsurprisingly, it’s complicated, and there are many unanswered questions.

The physiological significance of RSA is still essentially unknown, and many experts have “strong reservations regarding the validity of a number of heart rate variability (HRV) measures.”4 So it’s not at all certain that high HRV (as we can and do measure it) is actually a “good thing.”

It’s even less clear that we can tinker with it. Can you fiddle with RSA to raise your HRV? And does it matter if you do? Does driving up your HRV actually help you recover from the stress that might have pushed it down? Do slow exhalations actually reduce stress, or do they just reduce a measurement of stress? Maybe HRV is just an indicator, and changing it doesn’t change what it’s measuring any more than you can warm up a room by heating a thermometer.

“The effect of controlled breathing on RSA is not clear.”5

Unfortunately, HRV is made for pseudoscience: a noisy metric that contains any signal you want to find, about as objectively meaningful as a Rorsharch test.

Thought experiment: you are a champion HRV booster

Imagine that you definitely can raise your HRV. Like a master yogi, you have learned to control your physiology. Also imagine that this is helpful for some basic physiological function, like, say, efficiency of gas exchange.6

So you do that diligently. You do it for fifteen minutes per day while meditating — not a huge commitment, but more than most people ever do, a respectable and consistent effort.

That fifteen minutes is 1% of your 1440 minutes of daily breathing. Let’s be really generous and say that the effect lingers for a while: for two whole percent of your day, gas exchange in your lungs is slicker. Exciting stuff!

This would be like boasting about improving your commute with a modest boost to fuel efficiency … for 2% of your time on the road.

The point here is not to say that a higher HRV is futile … just that it’s hard for us to know if it’s actually a good value.7 And it’s rather unlikely. Even if HRV can be modified, and even if it has positive effects… it seems like a bit of a long shot that you can do enough of it to make a meaningful difference.

So do slow exhalations boost HRV, for whatever it’s worth?

For many years, I thought so. I took it for granted based on this dazzling logic: if hearts slow down during exhalation (and they really do), and that’s “healthy” (which is not so clear), then MOAR EXHALATION GOODER! This is the logical equivalent of:

• I get happier when I eat ice cream (and I really do).
• More ice cream might be healthy in some way, but it’s not super clear how (psychologically, perhaps).
• Therefore I should eat MOAR ICE CREAM!

The effect of the in/out ratio on HRV can certainly be tested. I found one directly relevant trial … which was negative. Tinkering with the in/out ratio had no impact on HRV as they measured it.8 Only the overall breathing rate had an impact on HRV, and not the ratio.

The end of the slow exhalations for me

Welp, so much for thirty years of thinking I should take my time exhaling. I think I’ll stop bothering.

I think it’s extremely unlikely that it does anything interesting relative to slow, deep breathing itself. •sad trombone• Slow, deep breathing may have health benefits — that’s a separate question, which I will tackle soon — but I no longer believe that slow exhalations are an upgrade.

Could slow exhalations have some other medical benefit that has nothing to do with HRV?

Yes. But is there any particular reason to suspect it? Not really, no.

Notes

1. Yasuma F, Hayano JI. Respiratory sinus arrhythmia: why does the heartbeat synchronize with respiratory rhythm? Chest. 2004 Feb;125(2):683–90. PubMed 14769752 ❐
2. Larsen PD, Tzeng YC, Sin PYW, Galletly DC. Respiratory sinus arrhythmia in conscious humans during spontaneous respiration. Respir Physiol Neurobiol. 2010 Nov;174(1-2):111–8. PubMed 20420940 ❐
3. Kim HG, Cheon EJ, Bai DS, Lee YH, Koo BH. Stress and Heart Rate Variability: A Meta-Analysis and Review of the Literature. Psychiatry Investig. 2018 Mar;15(3):235–245. PubMed 29486547 ❐ PainSci Bibliography 52076 ❐
4. Thomas BL, Claassen N, Becker P, Viljoen M. Validity of Commonly Used Heart Rate Variability Markers of Autonomic Nervous System Function. Neuropsychobiology. 2019;78(1):14–26. PubMed 30721903 ❐
5. Larsen PD, Tzeng YC, Sin PYW, Galletly DC. Respiratory sinus arrhythmia in conscious humans during spontaneous respiration. Respir Physiol Neurobiol. 2010 Nov;174(1-2):111–8. PubMed 20420940 ❐
6. Ben-Tal A, Shamailov SS, Paton JFR. Evaluating the physiological significance of respiratory sinus arrhythmia: looking beyond ventilation-perfusion efficiency. J Physiol. 2012 Apr;590(8):1989–2008. PubMed 22289913 ❐ PainSci Bibliography 52079 ❐
7. Houtveen JH, Hornsveld HK, van Trier J, van Doornen LJP. [Questioning the mechanism behind slow breathing and heart coherence training]. Tijdschr Psychiatr. 2012;54(10):879–88. PubMed 23074032 ❐
8. Paprika D, Gingl Z, Rudas L, Zöllei E. Hemodynamic effects of slow breathing: does the pattern matter beyond the rate? Acta Physiol Hung. 2014 Sep;101(3):273–81. PubMed 25183502 ❐