What Triggers the Vagal Response?

The vagal response occurs when the vagus nerve is stimulated. The vagus nerve is the longest nerve in the body. It runs from the brain stem to the chest and abdomen.

When this nerve is stimulated, it sets off a chain of events within the body. These changes can result in a wide variety of unpleasant sensations and symptoms.

The vagal response gets its name from the interplay between your vagus nerve and your blood vessels. The vagal response goes by a variety of names, including:

• Vasovagal reflex
• Vasovagal response
• Vasovagal attack
• Vagus reflex

This article explains the vagal response, its triggers, symptoms, causes, and how to cope.

Vagal Response Triggers

There are a variety of triggers that can set off the vagal response. Some of these triggers are internal, while others come from the environment. Common triggers include:

• Emotional stress
• Having blood drawn or the sight of blood
• Fear
• Gastrointestinal illness
• Having a bowel movement
• Heat
• Pain
• Standing for a long time
• Standing up quickly
• Trauma

Symptoms of the Vagal Response

Once a vagal response has been triggered, you may have a variety of physical symptoms. These include:

• Blurred or tunnel vision
• Cold and clammy skin
• Dizziness
• Fainting
• Feeling warm
• Light-headedness
• Nausea
• Ringing in ears
• Sweating
• Turning pale

Causes

The vagal response involves your central nervous system (brain and spinal cord), peripheral nervous system (nerves), and cardiovascular system (heart and blood vessels). When the reflex is triggered, it causes your blood pressure and heart rate to drop suddenly.

When this happens, the blood vessels in your legs may widen. This can cause blood to pool in your legs, which can cause your blood pressure to drop even further.

All of these changes can result in less blood flow to your brain. This may make you feel as if you might faint.

The strength of the vagal response and the resulting symptoms varies from person to person. Some people may pass out easily when they see blood or are afraid, while others may never have the response.

Vasovagal Syncope

No discussion of the vagal response is complete without a discussion of vasovagal syncope. With syncope, a person faints due to a drop in blood pressure and blood flow to the brain.

Vasovagal syncope can cause a person to pass out and fall to the ground. The loss of consciousness typically only lasts for a couple of minutes. Then, as blood flow returns to the brain, the person will wake up and return to normal consciousness.

What To Do in a Vasovagal Episode

A vasovagal episode can be frightening. But it's not usually a sign of a health emergency. Some things that may help include:

• Lie down for 10 minutes or so.
• Lower your head between your knees.
• Drink some water.
• Do not stand up quickly (this could put you at risk for fainting).

Prevention

You can't always prevent vagal episodes. But, some things may help to ward them off. These include:

• Getting good sleep
• Staying well hydrated
• Avoiding standing for extended periods of time

Summary

The vagal response is a series of unpleasant symptoms that occur when the vagus nerve is stimulated. Often, this response is triggered by certain things like stress, pain, and fear.

Symptoms of the vagal response include dizziness, nausea, ringing ears, and sweating. In some cases, it can make you pass out. This is called vasovagal syncope.

If you experience a vagal response, lie down for a few minutes or sit and place your head between your knees, and avoid standing quickly. Always tell your healthcare provider about these symptoms so that they can check for any other conditions.