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Can You Intentionally Activate The Sympathetic Nervous System With Breathing Techniques But Without Over-breathing?

In my last blog article I wrote about Wim Hof's amazing ability to survive in ice, by using a breathing technique that involves controlled over-breathing, and appears to work by boosting his adrenalin levels (and presumably activating his sympathetic nervous system which triggers adrenalin release).

That got me thinking - is there a way to intentionally activate the sympathetic nervous system using a breathing technique that doesn't involve over-breathing or hyperventilation?

Hormetic Stress?

Why would anyone want to do that, given that sympathetic activation is associated with anxiety and "fight-or-flight"?

Well, remember fight-or-flight evolved because it's a useful, adaptive response in danger situations. It mobiles resources so that you can more effectively deal with the threat or challenge.

Moreover, anything that induces a short bursts of sympathetic activation has a fair chance of being a hormetic stressor. A hormetic stressor is something that is healthy and adaptive in the slightly longer term because it triggers the body to strengthen itself in some way. An example is working out with weights - this creates slight damage in the muscles in the immediate term, but in the days following the body repairs this damage, plus a bit more, and you end up with stronger fitter muscles.

When it comes to emotional stress, the same applies - a short burst of relatively mild stress is actually a good thing because it's adaptive. But prolonged, chronic or overwhelming stress is, as we'd probably expect, more harmful.

So how might we induce a little short term sympathetic activation? My first idea was to investigate varying the inhalation to exhalation ratio (I to E ratio). I knew that having a relatively low ratio (0.5 to 0.8 or so) is thought to be more relaxing. In the yoga tradition there's a breathing technique based on a ratio of 1:2 - here's an article that describes breathing in this way.

Does anxiety and stress cause the inhalation to exhalation ratio to shift? We do know that anxiety leads to faster breathing and greater ventilation (and probably a degree of hyperventilation) but a quick internet search didn't show up any evidence that the I to E ratio is affected (or not affected - maybe no-one ever tested it).

However I did find a study that showed breathing slowly with a high I to E ratio versus a low one, changed the pattern of HRV or heart rate variability, strongly suggesting that the autonomic balance was different. The subjects of this experiment felt more relaxed with a lower I to E.

A Home Experiment Using Heart Coherence Biofeedback

I decided to try it for myself. I used my own software, both to guide my breathing (i.e. I used my breath pacer software which allows me to set I to E ratio) and to measure the effect on my HRV and in particular on heart coherence (for this I used Mind-Body Training Tools biofeedback software).

I breathed for about 10 minutes, at a breathing rate of 5.6 bpm which is quite natural for me, first using a low I to E ratio (40% to 60%) and then a high ratio (60% to 40%) while keeping the breathing rate constant throughout. (It should be said that I wasn't using the software to get feedback, I was simply recording what happened.)

Here's a graph of my breathing rate, showing that I was successful in keeping it steady and following the pacer (the vertical dotted line shows the change-over).

sine wave

This graph shows my inhalation to exhalation ratio - you can see it shifts markedly at the half way point, as you'd expect. (You can also see that I found it a lot harder to keep I to E steady in this phase.)

sine wave

What about HRV? My software calculates a "coherence score", and here is the session graph:

sine wave

You can see that my coherence score is relatively high a stable throughout the first ten minutes, then is significantly lower (maybe half its earlier level) in the second half of the session (with high I to E). (Coherence score does go to zero at the change-over - but ignore that as my movement caused the sensor to lose the signal for a short while).

Does this constitute evidence that I've activated my sympathetic nervous system? Possibly, but not necessarily, it may be simply a withdrawal of parasympathetic or vagal influence on the heart.

HRV is probably a much better measure of parasympathetic invluence than sympathetic. Maybe a better test would be to track skin conductance or galvanic skin response (GSR), perhaps skin temperature too, during the same kind of experiment. We know GSR reflects the sympathetic response much more directly. Perhaps that'll be my next blog post.

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