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Fainting (cont.)

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Vasovagal syncope

Vasovagal syncope is one of the most common causes of fainting. In this situation, the balance between the chemicals adrenaline and acetylcholine is disrupted. Adrenaline stimulates the body, including making the heart beat faster and blood vessels narrower, thereby increasing blood pressure. Acetylcholine does the opposite. When the vagus nerve is stimulated, excess acetylcholine is released, the heart rate slows and the blood vessels dilate, making it harder for blood to defeat gravity and be pumped to the brain. This temporary decrease in blood flow to the brain causes the syncopal (fainting) episode.

Pain can stimulate the vagus nerve and is a common cause of vasovagal syncope. Other noxious stimuli can do the same thing, including situational stressors. It is common for medical and nursing students to faint when observing their first operation or autopsy. Some people pass out when they hear bad news; others pass out when they experience the sight of blood or needles. In the Victorian age this was known as a "swoon."

Other situations commonly cause the heart rate to temporarily slow and cause a faint. Straining with urination, bowel movement, or coughing can cause a vagal response, increase acetylcholine levels and decrease blood flow to the brain.

Anemia

Anemia (low red blood cell count), whether it occurs acutely from bleeding or gradually for a variety of reasons, can cause fainting because there aren't enough red blood cells to deliver oxygen to the brain.

Dehydration

Dehydration, or lack of water in the body can similarly cause fainting or syncope. This can be caused by excessive loss of water from vomiting, diarrhea, sweating, or by inadequate fluid intake. Some illnesses like diabetes can cause dehydration by excess loss of water in the urine.

Medically Reviewed by a Doctor on 12/2/2013

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Source: MedicineNet.com
http://www.medicinenet.com/fainting/article.htm

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