What Triggers the Vagal Response?

The vagal response is an automatic response within our bodies that occurs as a result of stimulation of our vagus nerve. It gets its name from the fact that it involves an interplay between your vagus nerve and your blood vessels. When the vagus nerve is suddenly stimulated, it sets off a chain of events within the body. As you will see below, these changes can result in a wide variety of unpleasant sensations and symptoms.

The vagal response goes by a variety of names, including:

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

Vagal Response Triggers

There are a variety of triggers that can set off the vagal response. As you will see, some of these triggers are internal, while others come from the environment:

• Emotional stress
• Blood being 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 vasovagal reflex has been triggered, a variety of physical symptoms may be experienced. These include:

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

What's Going on in Your Body

The vagal response involves your central nervous system, your peripheral nervous system, and your cardiovascular system. When the reflex is triggered it causes an abrupt dropping of your blood pressure and a sudden reduction in your heart rate.

The blood vessels in your legs may widen, causing blood to pool in your legs, which can further drop your blood pressure. All of these changes can result in less blood flowing to your brain and trigger sensations that make you feel as if you might faint.

At its worst, the reflex can result in an actual brief loss of consciousness, a condition known as (vasovagal syncope).

It is important to know that experiencing episodes in which you have symptoms caused by a vagal response does not necessarily mean that there is something wrong with you. It is thought that the reflex is universal. What varies from person to person is the level of reactivity to triggers, on other words, how strongly you might experience symptoms from the reflex.

Vasovagal Syncope

No discussion of the vagal response is complete without bringing attention to the term vasovagal syncope. Syncope is the experience of fainting due to a drop in blood pressure and a subsequent decrease in the flow of blood to the brain. Thus vasovagal syncope is a loss of consciousness triggered by a vagal response.

Vasovagal syncope can cause a person to pass out and drop to the ground. With syncope, the state of unconsciousness typically only lasts for a couple of minutes. As blood flow returns to the brain, the person will return to a normal state of consciousness.

What to Do If You Experience Vasovagal Episodes

A vasovagal episode can be frightening but is usually not a sign of a health emergency. The best thing to do is to lie down for approximately 10 minutes or so. Another option is to lower your head between your knees.

Drinking some water may be of help as well. Whatever you do, do not stand up quickly as you put yourself at risk for fainting.

You may be able to prevent such episodes by getting good sleep, keeping yourself well-hydrated, and avoiding standing for extended periods of time. If you experience vasovagal symptoms when having a bowel movement, as some people who have irritable bowel syndrome experience, you may want to try to keep yourself relaxed, with your head down and your legs crossed as you sit on the toilet to try to keep your blood pressure steady.

Although the vagal response can be experienced by a person in fine health, it is always a good idea to let your physician know if this has happened to you.

Based on your symptoms and your medical history, your doctor will decide if further investigation is warranted.

Sources:

Raj S, Sheldon R. "Management of Postural Tachycardia Syndrome, Inappropriate Sinus Tachycardia and Vasovagal Syncope" Arrhythmia & Electrophysiology Review 2016;5(2):122-129.

"Syncope Information Page" National Institute of Neurological Disorders and Stroke.