I’ve come across a number of other people talking about the mechanics behind this technique. There are two different explanations that I’ve found, both of which work for me.
1. From Fight-Flight to Rest-Digest
As I’ve said, my elevated heart rate usually coincides with times of intense stress – when my fight-flight wiring is all-systems-go, and I’m barreling through life a mile a minute. We’ve all been there. It’s how a lot of us live, each and every day. But it can take a toll. And in my case, it can lead to my heart pounding out of control. So, if I can manage to take the edge off my fight-flight response, it can help my heart not have to race so often.
According to Coherence and The New Science of Breath (see http://www.coherence.com/science_full_html_production.htm)
Parasympathetic (rest and digest) nervous system activity is related to:
- bronchi (lungs) constriction
- carbon dioxide transferring out of the bloodstream
- decreased heart rate
- reduced arterial pressure and blood flow
- arterial relaxation and elastic contraction
And Sympathetic (fight-flight-freeze) nervous system activity is related to:
- bronchi (lungs) dilation
- transferring oxygen into the bloodstream
- increased heart rate, arterial pressure, and blood flow
These two systems are complimentary, so when we do things that strengthen one, we balance out the effects of the other. Too much of either one without the other is unhealthy. It can make us sick.
The Parasympathetic and Sympathetic nervous systems also both affect and are affected by the functions of our bodies, some of which we can control ourselves. Like our breath. So, we can actually get our systems to calm down – or speed up – by changing our breathing.
So, if I’m feeling stressed and on edge and in a fight-flight state of mind, by changing my breathing and activating my Parasympathetic nervous system, I can take the edge off my Sympathetic response.
It works the other way, too. If I’m feeling a bit too rest-and-digest-y, speeding up my breathing causes my Sympathetic nervous system to kick in and all systems come online in an alert state.
We’re all walking around in biological feedback machines. Our bodies respond to what we do, and we do things in response to what our bodies send back to us.
2. The Body Keeps Itself Going on Less Oxygen
Additionally, I’ve learned from a freediver (the intrepid people who go diving without oxygen tanks and learn to hold their breath underwater for as long as 11 minutes at a time) that when you hold your breath, your heart rate will necessarily lower, “because its a defense mechanism to prevent hypoxia (critically low blood oxygen). As your blood oxygen level is lowered, your heart rate will slow in order to conserve what little oxygen you have left.” (See the comments section at http://brokenbrilliant.wordpress.com/2010/04/02/how-i-learned-to-slow-my-heart-rate/)
I checked out a freediving website (http://www.impulseadventure.com/freedive/) and learned that holding your breath causes your body to slow the heart rate, so that it doesn’t use up all the oxygen. It also shunts blood away from the extremities so the brain still has enough oxygen – and does not kill brain cells.
On the site, they show a graph that shows how the heart rate decreases over the course of a 5:30 minute breath hold (which seems superhuman to me), then increases with the inhalation… and then decreases again to even lower than it was during the prior breath hold. I encourage you to check out the graph at http://www.impulseadventure.com/freedive/ — it’s very interesting.