What Is a Vasovagal Response?

Crowded spaces may cause some people to experience a vasovagal syncope.
A slow heart rate, or vasovagal syncope, causes a shortage of blood to the brain.
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  • Written By: Tricia Ellis-Christensen
  • Edited By: Jessica Seminara
  • Last Modified Date: 24 November 2014
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The vasovagal response is a complex signaling of the brain that dilates the blood vessels in the legs, slows the heart rate, and very often causes fainting, which is also called vasovagal syncope. This signaling begins with some outside stimulus such as being injured, seeing blood or getting an injection. People in the midst of an episode have similar symptoms, such as paleness, extra perspiration, and fainting. Some techniques used to manage an episode might help reduce fainting. Additionally, there are treatment options for people who often experience this problem.

In order to experience a vasovagal response, the body is first triggered by a stimulus, which awakens nerves that supply the vasomotor section of the brain. When the brain is activated, it signals the large veins in the legs to pen fully, which results in blood collecting in the legs at an abnormal rate. his draining of the blood also causes the heart rate to drop below normal. Once the process is complete, it's not at all uncommon for people to faint, and vasovagal syncope is believed to be the most common cause of fainting.

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The types of stimuli associated with a vasovagal response are highly varied. Sight of blood is a common cause, but other triggers might be much more complex. People who have experienced trauma might have a vasovagal response in any situation that reminds them of that trauma. These episodes are more likely to occur in dehydrated or recently ill individuals, and smokers may experience them more frequently. In some people, they may also happen right after exercise.

It’s relatively easy to recognize the symptoms of a vasovagal response in other people. Individuals are likely to look pale, have clammy skin and may perspire. Other symptoms people having a reaction may notice are faintness, nausea, and restriction of the vision or hearing.

If a person appears to be having a vasovagal reaction, it’s quite likely he may fall and sustain injury. Getting the affected individual to lie down with the head turned to the side may help restore some of the blood flow and prevent fainting. Lifting the legs, such as onto a chair from the lying down position, is also advised. Placing the head between the knees while sitting is an alternative position that may be of use.

Many individuals only have a vasovagal response a few times in their lives and don’t need any form of treatment for it. Some people may experience these episodes frequently, however, and might require help. One way to address this problem is psychotherapy to deal with the response to triggers or stimuli. Therapy is particularly important for those suffering from conditions like post traumatic stress disorder or specific phobias. Medications like antidepressants and beta blockers have also been shown to be useful for this condition.

In some patients the condition is so severe that their slow heart rate, known as bradycardia, must be treated. Doctors may consider pacemaker implantation in this case. A pacemaker can help reduce bradycardia episodes and thus prevent fainting.

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