What Is the Connection Between the Vagus Nerve and Fainting?

An overstimulation of the vagus nerve is the most common cause of fainting.
A diagram showing the vagus nerve.
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  • Written By: C.B. Fox
  • Edited By: Susan Barwick
  • Last Modified Date: 16 September 2014
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The vagus nerve and fainting are connected through an autonomic response known as vasovagal syncope. A frequently experienced condition, vasovagal syncope, which is sometimes called the vasovagal response, occurs when the vagus nerve directs too much blood away from the brain. Without a steady supply of oxygen, the brain quickly shuts down, and a person temporarily loses consciousness. In most cases, recovery from fainting connected to the vagus nerve is quick, and unless the patient was injured while fainting, medical attention for this type of fainting is not necessary.

In otherwise healthy patients, the vagus nerve and fainting are closely linked. Though there are a number of conditions that can cause a person to faint, an overstimulation of this nerve is the most common cause. This nerve is primarily responsible for connecting the digestive system, heart, and brain together and, in particular for diverting additional blood to the digestive system when needed. This system requires extra blood when digesting a large meal, passing solid waste, or vomiting. The main connection between the vagus nerve and fainting is that in some patients, the nerve can divert too much blood to the digestive system during these processes, causing a shortage in the brain and a resuting loss of consciousness.

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Aside from diverting blood away from the brain, the vagus nerve can cause a drop in blood pressure and the dilation of the blood vessels. This makes blood pool in the legs, away from the brain where it is needed to maintain consciousness. The blood flow returns to the brain and blood pressure returns to normal after a person faints and the vagus nerve is effectively reset.

People who are prone to vagus nerve overstimulation generally begin fainting in adolescence, though overstimulation of the vagus nerve, accompanied by fainting, can occur in any person at any age. If a person faints frequently, a doctor should be consulted to make sure that the vagus nerve is responsible. In the absence of any other medical conditions, such as a problem with the heart, fainting is not particularly dangerous, though a fall caused by a loss of consciousness can lead to injury.

It is also possible for an overstimulation of the vagus nerve and fainting to occur when a person becomes emotionally charged. Fear can often lead to fainting and it is not uncommon for patients with oversensitive vagus nerves to faint at the sight of blood, hypodermic needles, or other things that trigger a fear response. High stress situations can also lead to fainting.

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anon965491
Post 7

KoiwiGal -- Post 3: This not recommended to try, so please take my word that it has been done to me and please do not do it to others or yourself!

Trust me when I say the size of your hands and the strength in your body does not matter. If you push on the right parts of someone's throat they will lose consciousness; however, as soon as you remove the pressure they should wake up.

anon963953
Post 6

I have had four fainting spells in the last three years. They are usually associated with being in the sun, not eating earlier in the day, then consuming a large meal, some type of stomach cramps, then getting very hot, sweating, clammy and then I pass out for about 10 minutes.

I have had extensive work-ups to eliminate seizures. Now I realize that it is probably the vagus nerve.

anon322905
Post 5

Currently I have an issue with fainting and the fact that it could be my vagus nerve was brought up. Here is what happens during these fainting spells: I lose all color in my skin, my heart rate slows (to the point where it almost seems like it's not beating), my eyesight goes black and fuzzy starting with a ring on the outer edges of my eyes and moving inward, and it feels like I am falling asleep.

So far I have woken up within three minutes, but usually they only last around 10 seconds. Does this sound like vagus nerve issues or something different? I've been to doctors but they haven't given me a diagnosis.

anon258805
Post 4

Could arthritis in the neck somehow pinch the vagus nerve and cause the fainting symptoms?

KoiwiGal
Post 3

This is so great! I know it's a bit geeky but this makes me think so much of the Vulcan nerve pinch on Star Trek.

That was what it was called when Spock, or another Vulcan, would pinch the neck of a human and make them faint. I was never sure if they were just strong enough to do it, or if they were supposed to be precise enough to know the right place.

The vagus nerve is even sort of in the right place, because it does goes up the neck. I very much doubt there is actually a way to pinch it and make someone faint though (especially without possibly hurting them. It does involve the blood flow to the brain after all). But it still tickles the science geek in me that there might be some truth to the TV show.

indigomoth
Post 2

I guess this was the reason that women used to faint so much back in the day. They would tie their clothes so tightly they couldn't breathe properly and probably put pressure on their vagus nerve. I imagine they were almost expected to react emotionally to things, so that probably didn't help much either.

It's a shame that all these things combined to enforce the image of a woman as being near hysterical, that I still think has some implications to this day. Because in reality, I know very few people, men or women, who have ever fainted, and I would think it very unusual for someone to do some simply because they were put in trying circumstances.

pastanaga
Post 1

When I was a child I had a few fainting spells. Everything would disappear in what was kind of like static, although I don't remember it very well.

My mother was terrified that I had epilepsy or something else wrong and I remember an extremely tense visit to the doctor.

It turns out it was something like a migraine headache and he explained it would probably clear up on its own.

In the end it did, quite quickly. My mother remained anxious about it for what seemed like years afterwards though, and I guess I can't blame her. I'm glad it didn't happen when I was learning to drive or anything like that!

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