Syncope, situational: The temporary loss of consciousness in a particular kind of situation. The situations that trigger this reaction are diverse, and include having blood drawn, straining while urinating or defecating, and coughing. It can also be due to the emotional stress, fear, or pain. When experiencing the trigger condition, the person often becomes pale and feels nauseated, sweaty, and weak just before losing consciousness. Situational syncope is caused by 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 leads the nerves that serve 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 circulating blood tends to go into the legs rather than to the head. The brain is deprived of oxygen, and the fainting episode occurs.
Reviewed on 12/27/2018
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