Vasovagal reaction

Vasovagal reaction
A reflex of the involuntary nervous system called the vasovagal reaction. The vasovagal reaction leads the heart to slow down (bradycardia) and, at the same time, it effects the nerves to the blood vessels in the legs to permit those vessels to dilate (widen). The result is that the heart puts out less blood, the blood pressure drops, and what blood is circulating tends to go into the legs rather than to the head. The brain is deprived of oxygen and the fainting episode occurs. This sequence of events may lead to a temporary loss of consciousness in a particular kind of situation. (Syncope is temporary loss of consciousness or, in plain English, fainting). The situations that trigger this reaction are diverse and include having blood drawn, straining while urinating or defecating or coughing. The reaction also can be due to the emotional stress of fear or pain. Under these conditions, people often become pale and feel nauseated, sweaty, and weak just before they lose consciousness. The vasovagal reaction is also called a vasovagal attack. The resultant fainting is synonymous with situational syncope, vasovagal syncope, vasodepressor syncope, and Gower syndrome which is named for Sir William Richard Gower (1845-1915), a famous English neurologist whose name is also associated with a sign, a solution, another syndrome, and a tract in the central nervous system.

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see under syncope.

Medical dictionary. 2011.

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