The Body in Conversation. Part 9: The Vagus Nerve - Listening to the Body

Following on from Part 8, The Phrenic Nerve, if the phrenic nerve is the direct line that tells your diaphragm to contract, the vagus nerve is part of a much bigger, almost whole-body, full-room party chat.

The vagus nerve is so often talked about these days as though it were simply a big calming switch. Stimulate your vagus nerve. Activate your vagus nerve. Switch on your parasympathetic nervous system. Breathe and calm yourself right down.

As usual, the real story is much more interesting than that.

The vagus nerve is one of the major communication routes between your brain and many of your internal organs. It begins in the brainstem, travels down through the neck and into the chest, where it passes close to the heart and lungs, then continues alongside the oesophagus towards the diaphragm and abdomen.

Its name comes from the Latin word vagus, meaning wandering, which feels very appropriate because it really does wander through the body, sending branches out along the way and gathering information back in.

And that last bit is the part I find particularly cool and mind-blowing.

We tend to imagine nerves as wires carrying instructions from the brain out towards the body, as though the brain is the boss and everything below it simply waits for orders.

But that isn’t actually how this works.

A huge amount of vagal information is travelling in the opposite direction, from the body back towards the brain.

The body is continually reporting in.

Your heart is reporting in. Your lungs are reporting in. Your gut is reporting in. Changes in stretch, pressure, digestion, blood pressure, breathing and the internal environment are being detected and relayed, much of it without ever becoming part of your conscious awareness.

You are not sitting there thinking about exactly what your stomach is doing every second or whether your heart has subtly changed its rhythm.

Thankfully, because that would be far too much information and leave very little room for important intellectual decisions like what to cook for dinner.

But your brain is still receiving all of that information and adjusting what happens next.

So rather than imagining the vagus nerve as an ON switch for calm, I prefer to think of it as a messenger.

A very busy messenger.

The body is continually speaking to the brain, and the brain is continually responding.

When doctors actually cut the vagus nerve

There is a rather extraordinary bit of medical history here too.

For much of the twentieth century, stomach ulcers were thought to be largely a problem of too much stomach acid.

Doctors already knew that the vagus nerve played a role in stimulating the stomach to produce acid, so the logic became surprisingly straightforward.

If the vagus nerve is telling the stomach to make acid, perhaps we can reduce the acid by cutting the nerve.

Which is exactly what surgeons started doing.

The operation was called a vagotomy.

By the 1940s, vagotomy was being used as a treatment for severe duodenal ulcers, and for several decades it became an important surgical treatment for peptic ulcer disease.

Just pause on that for a moment.

People had parts of their vagus nerve deliberately cut in order to reduce the amount of acid their stomach produced.

And it did reduce acid.

But, of course, the vagus nerve was not only involved in acid secretion.

It was also involved in the movement and emptying of the stomach.

So when surgeons interrupted that communication, they discovered that they had changed much more than stomach acid.

Some people developed delayed gastric emptying, diarrhoea, vomiting and other digestive problems. Surgeons sometimes had to combine vagotomy with additional procedures, such as a pyloroplasty, to help the stomach empty properly.

Which is such a brilliant example of the whole point of this series.

The body is never doing just one thing.

Medicine had identified one very real relationship. The vagus nerve helped stimulate gastric acid secretion.

So they altered that relationship.

But the vagus nerve was also part of a much bigger conversation involving movement, secretion and communication throughout the digestive system.

You could change one part of the conversation, but you could not neatly remove it from everything else the nerve was involved in.

And then the story changed again.

As medications that suppressed stomach acid became increasingly effective, and as our understanding of Helicobacter pylori transformed what we knew about many stomach ulcers, vagotomy gradually became far less common.

I love this bit of history because it reminds us that medicine evolves.

The surgeons were not foolish to cut the vagus nerve. They were working with the knowledge and treatments they had at the time, and vagotomy genuinely helped many people.

But as our understanding of the stomach, bacteria, acid secretion and the nervous system grew, treatment changed too.

And if that story tells us anything, it is that the vagus nerve is never doing just one thing.

Which brings us back to breathing.

So what has the vagus nerve got to do with breathing?

The vagus nerve does not make the diaphragm contract.

That is the job of the phrenic nerve, which we explored in the last part of this series.

But we also know that breathing does not happen in isolation.

Neither does heart rate.

Neither does digestion.

And neither does the way your nervous system responds to what is happening around you.

Imagine you have just finished eating and you are sitting comfortably at the table. There is no immediate threat. Your breathing can be easy, your heart does not need to race and your digestive system can quietly get on with the job of dealing with your dinner.

Then imagine there is suddenly a huge crash behind you.

Before you have even consciously worked out what happened, your body has already changed.

Your breathing alters. Your heart responds. Your attention sharpens. Your muscles prepare. Digestion suddenly becomes rather less important than finding out whether something is about to land on your head.

Nothing has happened in isolation.

Your body has reorganised itself according to what it thinks is happening.

That is the bit I find endlessly fascinating, and if you have been following this series you probably know that by now.

You are not a collection of separate systems.

Your heart is not doing one thing while your lungs do another and your gut quietly gets on with digestion somewhere downstairs.

They are in conversation.

And the vagus nerve is one of the major routes through which that conversation happens.

Its anatomy makes that even more interesting.

The right and left vagus nerves descend through the chest and contribute to networks around the oesophagus. As the oesophagus passes through the diaphragm, vagal fibres travel with it through the oesophageal opening and continue into the abdomen.

So once again, the diaphragm is not simply a sheet of muscle separating the chest from the abdomen.

Important structures are passing through it and information is travelling with them. The chest and abdomen are communicating across it, and breathing is happening right alongside all of that.

Does a long exhale really “switch on” your vagus nerve?

This is where some of the claims made about breathing and the vagus nerve become a little too neat.

You will often hear that a long exhale “switches on” the vagus nerve or that one particular breathing technique “activates” the parasympathetic nervous system.

The reality is much more nuanced.

Breathing changes pressure within the chest. It alters the biomechanical relationships between the lungs, heart and blood vessels. It affects blood flow and heart rate, while receptors throughout the cardiovascular and respiratory systems are continually sensing what is happening and feeding information back towards the brainstem.

One of the loveliest ways to see this relationship is through something called respiratory sinus arrhythmia.

The word arrhythmia makes it sound as though something has gone wrong with the heart, but in this case it is usually a normal part of healthy physiology.

As you breathe in, your heart rate tends to speed up slightly.

As you breathe out, it tends to slow down again.

So your heart is not beating at one perfectly fixed speed while you breathe. Its rhythm is subtly rising and falling with your respiratory rhythm.

Why?

Partly because breathing changes what is happening mechanically inside the chest. When the diaphragm contracts and descends, pressure inside the thorax changes and this influences how blood returns to the heart.

At the same time, the nervous system is receiving information about what is happening inside the heart, blood vessels and lungs.

During inhalation, vagal influence on the heart is temporarily reduced and the heart rate tends to rise slightly.

As you exhale, vagal influence increases again and the heart rate tends to fall.

The changes are tiny.

You may never consciously feel them.

But beat by beat, breath by breath, your heart and respiratory system are adjusting to one another.

I love this because it gives us a measurable example of what I mean when I keep talking about conversation.

Your breath is not simply moving air in and out of your lungs.

The mechanical changes created by breathing are being sensed by the body, information is travelling back towards the brainstem and the nervous system is adjusting the heart in response.

So yes, breathing and vagal activity are connected.

But respiratory sinus arrhythmia is not evidence that every long exhale simply flicks a “vagus switch” and suddenly makes you calm.

It shows us something much more interesting.

Breathing, circulation, the heart and the autonomic nervous system are continually adjusting to one another.

And the nervous system is also combining that information with everything else that is happening.

What you are seeing and hearing matters. Whether you are sitting still or climbing a hill matters. Whether you are frightened, excited, cold, hungry or safe matters.

Breathing is part of the conversation.

It is not the whole conversation.

Why I still think breath is incredibly powerful

I work with breathing every day, so I am certainly not arguing that breathing is unimportant.

Quite the opposite.

I think breathing is powerful precisely because it is already woven into so many other systems.

It does not sit outside the nervous system and somehow control it from above.

It is part of it.

Change the breath and you change one part of the information the body is receiving.

Sometimes that shift is enough to make a noticeable difference.

Sometimes the change is gradual.

And sometimes the body is dealing with something much bigger, and one slow breath is not going to magically override everything else.

That does not make breathing useless.

It just makes the body more interesting.

Your gut already knows this

The same is true when we think about the relationship between the brain and the gut.

Anyone who has ever felt sick with nerves already knows that these systems are connected.

You do not need to understand the anatomy of the vagus nerve to know that a difficult conversation can suddenly change your stomach, or that stress can alter your digestion, or that you can feel something in your gut before you have consciously put words around what you are feeling.

The gut is not sitting silently waiting for commands from the brain.

It is communicating back.

And the vagus nerve is one of the major pathways involved in carrying that information.

Again, conversation rather than command.

A few ways to actually feel some of this happening

I always like to give you something to try, because anatomy gets much more interesting when you can feel even a tiny bit of it happening in your own body.

The easiest place to start is with your pulse.

Sit quietly for a moment and find your pulse at your wrist or gently at the side of your neck.

Don’t change your breathing yet.

Just notice the rhythm.

Then take a slow, comfortable breath in and let the breath out easily.

You may notice that your pulse changes ever so slightly.

It often speeds up a little as you inhale and slows again as you exhale.

You might not catch it straight away, and that is absolutely fine. Don’t force the breath or turn it into another thing to achieve.

Just become curious.

Can you feel the rhythm of your heart changing with the rhythm of your breathing?

That tiny rise and fall is respiratory sinus arrhythmia.

Your heartbeat and your breath are literally adjusting to one another.

And I think that is pretty amazing.

You can then try making the breath slightly slower.

Nothing enormous.

Perhaps around five seconds in and five seconds out for a few breaths.

Again, just notice.

You might become more aware of the relationship between the breath and your pulse.

Then try humming.

Take a comfortable breath in and hum gently as you breathe out.

You don’t have to vibrate the windows.

Just notice what happens.

The exhale becomes longer almost automatically. You can feel vibration through the throat, jaw, face and chest, and suddenly the breath is not only something you can feel.

You can hear it too.

I like humming because it makes the breath tangible.

You could even alternate between one humming breath and one normal breath and notice whether anything changes.

Not whether it is better.

Not whether you are calmer.

Just whether it feels different.

Because that is what we are interested in.

Information changing.

The body responding.

The conversation shifting.

And then there is cold water.

Cold water on the face can trigger part of what is known as the diving response.

Humans, like other mammals, have reflexes designed to respond when the face is cooled, particularly around the forehead, eyes and nose.

Sensory information from the face travels towards the brainstem, and the cardiovascular system begins to reorganise.

Heart rate can slow while blood vessels in other areas constrict.

Once again, several systems are responding together.

This is not simply “cold water switches on your vagus nerve”.

The diving response involves several branches of the nervous system and can also increase sympathetic activity and blood pressure.

So I would not suggest throwing your face into a bucket of ice in the name of vagal tone.

But as a piece of human physiology, it is fantastic.

Cold touches the face.

A signal travels into the nervous system.

The brainstem responds.

Heart and circulation alter.

One event.

A whole-body response.

And where does the pelvic floor fit into all of this?

The vagus nerve does not directly innervate the pelvic floor muscles, and I think it is important not to muddy that.

But the pelvic floor lives inside the same person whose breathing, digestion, abdominal pressure, movement and nervous-system state are continually changing.

If breathing becomes restricted, the mechanics of the trunk change.

If digestion changes, pressure and sensation within the abdomen can change.

If the nervous system is persistently on alert, muscle tone and movement strategies can change too.

So I would never say, “Stimulate your vagus nerve and your pelvic floor will relax.”

That is just way too simple.

What I would say is that the pelvic floor lives inside a whole human.

And that whole human is constantly responding to breath, stress, movement, digestion, sensation, environment and perceived safety.

Which, really, is the theme we keep coming back to throughout this entire series.

Nothing is working alone.

The diaphragm is not working alone.

The abdominal wall is not working alone.

The pelvic floor is not working alone.

And the vagus nerve is not simply a calming wire waiting for you to hack it.

It is listening.

It is carrying information.

It is helping the brain understand what is happening inside the body.

Perhaps that is the most interesting thing about it.

Not that we can “activate” it.

But that it is already there, all day and all night, quietly carrying messages between the body and the brain.

Keeping the conversation going.

And next, we are widening the conversation again.

Because your diaphragm is not just talking to your heart, lungs, gut and nervous system.

Breathing changes what happens much further afield too.

Your jaw.

Your tongue.

Your throat.

Your eyes.

Your hands.

Your feet.

So in Part 10, we are going to look at some of the less obvious places your breath shows up in your body, and why those connections matter.

Because the body is always talking.

If you are loving my joined up thinking for pelvic health and would like to work with me: Abby