Breathing is the most important action we perform. We can live without moving for several decades, without eating for several months, without drinking for several days, but without breathing only for a matter of minutes.

While the world breath holding record (with intensive training and under special conditions) is over 24 minutes (!!) most people struggle within 30 seconds of holding the breath and would become unconscious after 5 minutes of oxygen deprivation.

Just as you can be unconscious about the way you move the body or eat, you can also be unconscious about the way you breathe. As breathing is the most important or essential action, there should be no surprise that the way you breathe has a large impact on one's health - both physical and mental.

This interesting article (although most of this information already appeared in an article I wrote a few months ago) was, no doubt, inspired by the recently published book "Breath: The New Science of a Lost Art" by James Nestor:

https://elemental.medium.com/how-nasal-breathing-keeps-you-healthier-3695bb5c6cd1

I really wanted to love this book but, unfortunately, it proved to be a disappointment. This is probably because the author had already written so extensively about the subject in his excellent and fascinating book "Deep: Freediving, Renegade Science, and What the Ocean Tells Us about Ourselves."

The book is particularly disappointing because it only gives superficial treatment to the ancient practice of pranayama. But one feature that does stand out as a central theme is a scientific experiment undertaken by the author that compares nose and mouth breathing.

The experiment reveals conclusively that nose breathing is far superior to mouth breathing - something that is already evident to all yoga practitioners. At least the experiment offers concrete evidence of this fact.

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One of the fascinating subjects Nestor explores in his book Deep is something called the dive reflex.

The breath holding record of 24 minutes mentioned above was only possible under special circumstances: it involves hyperventilating oxygen for 30 minutes and can only be achieved under water. Without oxygen, the record is something over 11 minutes under water. But above water, it is only possible to hold your breath for half that time - around 5 minutes.

The reason for this is something called the Mammalian Dive Reflex: when submerged in cold water, mammals can hold their breath for twice as long. In fact, even just wetting one's face with cool water, initiates the reflex.

Some aquatic mammals such as seals, that have a resting heart rate similar to humans of around 60 beats per minute, reduce their heart rate to just 10 beats per minute and are able to go without breathing for up to one hour when submerged. But this effect happens to all mammals when submerged to some extent.

There are two main changes that occur in the body due to the reflex - the heart rate slows 10-30% (up to 50% in trained freedivers) and the peripheral blood vessels contract, reducing blood circulation to the extremities, reducing blood pressure and ensuring that the brain and heart receive ample oxygen.

These two effects also take place to some extent simply by holding the breath even without submerging the body in water. This may explain how yogis can reduce their heart rate through pranayama and breath holding.

The dive reflex is initiated simply by putting the face in cold water. The science is not fully understood, but it is thought that a stimulation of the trigeminal nerve (the 5th cranial nerve) initiates a response via the vagus nerve (10th cranial nerve) that controls heart rate along with most other autonomic functions.

The vagus nerve - from the latin "wanderer" innervates and controls the functions of most vital organs in the body as it wanders down from the brain stem through the neck and into the thorax. Although vagus nerve is used in the singular it is actually a pair of nerves that innervate left and right side.

I have often thought that there must be a relation between the vagus nerve and the ida and pingala nadis. Although ida and pingala are said not to be restricted to the nerve pathways and are sometimes said to extend outside the body, all "tubes" in the body are called nadis. The word nadi means "river". Blood vessels are nadis, as are nerves, intestines or any anatomical tubes.

The vagus nerve extends only as far down as the upper part of the descending colon, while ida and pingala are said to start at the muladhara, so these two are not identical anatomically, but when you add the other component of the autonomic nervous system - the sacral plexus that innervates the lower abdomen that would be "toned" by the application of mula and uddiyana bandha, together with the vagus nerve, it would seem that perhaps the energetic sensations experienced during pranayama practice may be associated with these two nadis/nerve systems.

Manual stimulation of the vagus nerve in the neck and an associated practice of carotid sinus stimulation are used medically for various conditions including the treatment of heart failure, the reduction of elevated heart rate and controlling seizures.

In pranayama practice, in addition to breath holding, one also applies three bandhas - mula, uddiyana and jalandhara. Jalandhara bandha involves pressing the chin down to the chest and involves the constriction of the throat and some pressure on the vagus nerve. I have a suspicion that JB may have a similar effect to these medical techniques used to bring the system into balance - slow down the heart rate, reduce blood pressure and calming the mind.

The dive reflex is also initiated to some extent simply by breath holding. I suspect that the application of the bandhas, enhances the effect.

Yoga practices are designed to increase the sattva (calmness) quality by reducing the tamasic (dullness) and rajasic (stress) elements and recommends bathing before practice to initiate this process. Most people would feel inclined to take a hot shower to get the body warmed up and flexible, however the yogic recommendation is to bathe in cold water. The dive reflex only works through immersion in water less than 21C. Even more profound effects can be obtained by submersion in ice water as popularized by Wim Hof.

Vagus nerve stimulation is a buzz word/theme in today's treatment of trauma. The effect of trauma or PTSD is two-fold - one is an elevated fight/flight response - an excess of rajas - another is the opposite - when a creature is threatened by a predator an alternative response is to play dead - an excess of tamas energy.

What do you do when you feel stressed, anxious or angry - you may feel inclined to splash your face with cold water. The reason this is effective is that it initiates a very real anatomical effect.