What Triggers the Vagal Response?

The vagal response (vasovagal reflex) is when stimulation of the vagus nerve causes symptoms such as lightheadedness, sweating, and blurred vision. This can happen because of stress, pain, heat, having a bowel movement, or even standing too long.

In some cases, vasovagal syncope—a typically brief episode of passing out—can also occur.

This article explains the vagal response and its causes. It discusses symptoms you may experience, how a vagal response episode is treated, and some ways you can prevent one from occurring.

Vagal Response Causes

The vagal response is a neurocardiogenic response. This means it involves your central nervous system (brain and spinal cord), peripheral nervous system (nerves), and cardiovascular system (heart and blood vessels).

The vagal response causes your blood pressure and heart rate to drop suddenly. When this happens, the blood vessels in your legs may dilate, or 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.

Vasal Response Triggers

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

Common triggers of the vagal response include:

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

Some people may experience vasovagal episodes as a side effect of medication. Be sure to discuss the possibility with your healthcare provider.

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
• Lightheadedness
• Nausea
• Ringing in ears
• Sweating
• Turning pale

The strength of the vagal response and the resulting symptoms vary from person to person.

Vasovagal Syncope

Vasovagal syncope is a loss of consciousness triggered by a vagal response. With this, 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. The loss of consciousness typically only lasts for a couple of minutes.

As blood flow returns to the brain, the person will wake up and return to normal consciousness.

A vagal response that causes syncope isn't usually serious. It can, however, be the sign of a serious condition like heart arrhythmias or even a sudden heart attack. It also can lead to serious injury from a fall.

What To Do During a Vasovagal Episode

A vasovagal episode is not usually a sign of a health emergency. Some things that may help resolve the episode include:

• Lying down to improve blood flow to the brain
• Positioning your head between your knees
• Drinking some water
• Not standing up too quickly, so as to avoid the risk for fainting

Prevention

The vagal response can't always be prevented, but some measures may help to ward off episodes. These include:

• Getting good sleep
• Staying well hydrated
• Avoiding standing for extended periods of time
• Dressing in light, breathable fabrics so that you don't get overheated

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.