Photo: Rafael Alves
As a potential means of directly reducing inflammation in the body, vagus nerve stimulation (VNS) is getting a lot of people excited.
The vagus nerve - which runs between our brains and our stomachs - is the human body's longest cranial nerve.
It won't be too long before the electronic stimulation of it is helping to treat inflammatory illness, says bioelectronic medicine specialist Kevin Tracey.
"This is a new world that we're pursuing and it's gonna have direct implications for better clinical therapies for patients someday. Not a hundred years from now, in the coming years you're gonna see a lot more [VNS] therapies used in the clinic is my firm belief."
- Related: What is the vagus nerve?
Back in the late '90s, Professor Tracey tells Kim Hill, he was one of the scientists who first discovered the vagus nerve was the channel of communication between our brains and bodies on how to help balance and control inflammation.
The discovery was made after a small amount of a drug the scientists had invented to deactivate brain inflammation also helped to reduce the white-blood-cell activation that leads to inflammation in our bodies, he says.
When white blood cells encounter an injury (such as a cut or bruise) or an infection (like a bacteria or virus), they get "revved up", Professor Tracey says, and in turn produce molecules that cause inflammation in the body in the form of redness, pain, swelling and loss of function.
After guessing that the drug administered to a brain was sending its calming signals to the body via the vagus nerve, the scientists tried cutting it in the body of a cow, Professor Tracey says. When they did so, the drug stopped controlling inflammation in the cow's body.
"We discovered the signals in the vagus nerve were like the brakes on your car, slowing down inflammation, and if we cut the brakes, inflammation raced out of control."
Suspecting the messages being sent via the vagus nerve were electrical in nature, the scientists then discovered electric stimulation of the nerve could deactivate the body's inflammatory response.
There must be a reason we still have the vagus nerve's inflammatory reflex, he says, as it is "evolutionarily ancient".
"The fact that evolution preserved this reflex is because it is a 'natural' or 'inherent' property of the nervous system and the immune system ... Evolution doesn't retain things that are bad for you unless they are outweighed by significant advantages."
The possibility of electrically stimulating the vagus nerve in order to treat autoimmune conditions was one that Professor Tracey first wrote on the back of a napkin in 1998.
Fast forward to 2016, and he says the "game-changing" results of 20 years of clinical trials with VNS implants showed stimulation decreased pain and swelling in the joints and limbs of people with rheumatoid arthritis.
Professor Kevin Tracey of the Feinstein Institutes for Medical Research in Manhasset, New York Photo: Feinstein Institutes for Medical Research
Before treatments can be "perfected", though, Professor Tracey says a deeper understanding of the mechanisms by which VNS can modulate a disease is needed.
Scientists don't yet know, for example, how and why the treatment has been shown to help around half the people with drug-resistant epilepsy who've trialed it.
"That's really the step we're in now - breaking down the clinical diseases or syndromes into those which we know the mechanism and those we don't know the mechanism, and then developing methods to study those mechanisms.
"It's about doing more science and doing clinical trials."
As we await more scientific backing for effective VNS treatments, Professor Tracey warns of online misinformation about the vagus nerve which could be potentially dangerous.
'Vagal tone' - purported to be a measure of vagus nerve activity - is a phrase frequently used on social media that he neither understands nor uses.
To measure the health of a vagus nerve, heart rate is the best method we know of so far, Professor Tracey says.
"If your heat beat is slow, that's a very good sign you have very good vagus nerve activity. That's probably as close as you can get to a gold standard.
"People who exercise regularly, have healthy diets and get enough rest tend to have slower pulse rates, so that is probably a good place to start ... that's a sign that you're taking care of your vagus nerve."
The "basic physiology" of how the vagus nerve may be affected by breath-holding, cold showers and meditation isn't yet known, he says,
Severe cold water exposure and/or breath-holding (as practised by Dutch motivational speaker Wim Hof) has been shown to activate several nerves, including the vagus nerve, and also slow the heart rate.
While Professor Tracey finds it "interesting and intriguing" that Wim Hof has proven himself able to suppress the amount of inflammation in his bloodstream via breath-holding, we don't yet understand why.
He notes that people interested in exploring VNS should check with their doctor about what's appropriate and safe. Ice baths and breath-holding aren't for everybody and can be dangerous for some people.
An illustration of the placement of a vague nerve stimulation implant Photo: @ Mayo Foundation for Medical Education and Research
In the meantime, Professor Tracey is looking forward to the upcoming completion of a large clinical study in which 250 people with severe rheumatoid arthritis were fitted with VNS implants.
"If the results are positive, it will pave the way for many patients in future to have VNS implants.
"That will allow us to learn a lot more… about whether this idea can be tested in other conditions like Crohn's disease, potentially multiple sclerosis or psoriatic arthritis. The list goes on and on because inflammation is so important to [many of] these conditions."
The "new world" of bioelectronic medicine will directly lead to the development of better clinical therapies. And those could emerge sooner than you might imagine, Professor Tracey says.
After 30 years of clinical trials into the potential side effects and complications of VNS, he says the treatment has proven to be quite safe.
With a third of today's pharmaceutical drugs "far from perfect", we are just starting to "harness the power" of bioelectronic medical treatment, Professor Tracey says.
"It has the potential to be extremely disruptive - to the benefit of patients."
Professor Kevin Tracey is a professor of molecular medicine and neurosurgery at the Feinstein Institutes for Medical Research in Manhasset, New York.
