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Slow exhalations: are they a meditative breathing upgrade? (Member Post)

 •  • by Paul Ingraham
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Taking a little extra time with breathing out is thought to be even more relaxing and healthful than simply taking slow, deep breaths with roughly equal inhalations and exhalations. Is it really, though?

I ran into this question a few weeks ago 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. Right? But as I attempted to explain the rationale for it, I hit some snags. I went digging for more evidence … and that didn’t go super well.

Just once, I’d like to check my assumptions and just have them confirmed, but it never seems to go that way. Assumptions, by nature, are usually wrong. So here I am, consuming yet more humble pie. (If you’re keeping score, this is my second “I made a mistake” post in a row.)

I was wrong about slow exhalations, but 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:

“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 things down — but it’s also so much more complicated than that.

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Heart rate and breathing

Photo of a man in a business suit meditating in.

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): an inconsistency in the heart rhythm linked to respiration. Just an odd little thing our bodies do (Yasuma 2004).

Every animal with a spine does this, and we don’t really know why (Larsen 2010). But the general 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 lately has been 34 milliseconds: that is, the gap between my heartbeats is 34ms longer during exhalation than inhalation.

Ahhh. 34ms 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 (Kim 2018).

And therefore: Less HRV bad! More HRV good! And that clinches the deal: exhalation must be healthy, 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 & 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 & 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) & that seems like a really definite source of physiological stress.

Can we control HRV with breathing and does it matter?

We know that the RSA is a thing bodies do, and we know that we can roughly measure it with HRV, and it seems like that number is 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.” (Thomas 2019) So it’s not at all certain that high HRV (as we can and do measure) 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.” (Larsen 2010)

Thought experiment: you are a champion HRV booster

Just imagine, for the sake of argument, that you definitely can raise your HRV. And also imagine that this is definitely helpful for some basic physiological function, like, say, efficiency of gas exchange (Ben-Tal 2012).

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 somewhat slicker. Exciting stuff!

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

The point of this thought experiment 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 (Houtveen 2012), whereby “hard” I mean “probably impossible.”

And the point is that it’s a bit unlikely.

So do slow exhalations boost HRV best, 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 (Paprika 2014; yes, “Paprika”). 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 don’t think I'll bother with that anymore.

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. Is there any particular reason to suspect it? Not really, no.