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Syncope simply means fainting or the sudden loss of consciousness. Fainting usually results after the brain has been deprived of oxygen and blood for about ten seconds. Syncope can be caused by any number of conditions that result in the deprivation of oxygen and blood from the brain.

The general causes of fainting include cardiac problems, diseases of the brain, and a variety of abnormalities of the arteries and veins that secondarily cause inadequate blood flow to the brain. Most commonly, it is caused by an abnormal reaction of the vagus nerve, which can temporarily cause a slow heart rate and a decrease in blood to the brain.

This phenomenon, known as a vasovagal response or vasovagal syncope, can be caused by fright (as sometimes happens when donating blood), pain, or trauma.Syncope is considered a otentially serious symptom, although most of the time it has a benign cause.For example, Victorian ladies who swooned whenover whelmed by a great emotional event did not have a serious underlying disease.

The most common cardiac cause of syncope is an irregular heartbeat or arrhythmia, especially a type of arrhythmia called heart block. This condition is characterized by an extremely slow heartbeat that results in an inadequate blood and oxygen supply being pumped to the brain. Very rapid heartbeats (usually more than 150 beats per minute) also can cause the heart to pump inefficiently, sending an insufficient amount of blood to the brain.

Syncope also maybe due to an obstruction in the blood vessels in the neck that carry blood and oxygen to the brain. A very narrowed valve leading out of the heart may prevent adequate blood from reaching the brain; this also can cause syncope. Or a heart attack may result in fainting when the heart muscle becomes severely weakened and stops pumping temporarily,

This is not, however, a common symptom of heart attack. When fainting occurs frequently, it maybe due to a narrowing of the carotid arteries, which serve as conduits for blood and oxygen to the brain. Less common, and generally less serious, is fainting that occurs with a condition resulting from an overactive carotid sinus reflex. This occurs when a person turns his or her head and activates the reflex, which temporarily slows the heart rate and decreases blood pressure.

Some people can experience syncope after standing still, especially with the knees locked for long periods of time, as do soldiers standing at attention, or people at a cocktail party in a hot room, or singers standing in a church choir. Blood pools in the legs, leading to an inadequate blood flow to the heart and then to the brain. In younger people, this is probably only a temporary condition that can be relieved by changing posture, moving the legs around, or sitting

Fainting can also be caused by an abnormal metabolic condition, such as occurs when a diabetic patient takes too much insulin. If an individualís blood sugar levels fall too low, the blood may not be able to carry enough oxygen to nourish the brain.
Micturition (urination) syncope is a form of fainting that typically occurs in the middle of the night in elderly men with prostate problems.
This happens when blood flow is temporarily diverted from the brain as the individual stands from a reclining position or when he must bear down in order to urinate. This is not common, but should be considered before a lot of tests to look for more serious problems are scheduled.
Other noncardiac causes of syncope include hyperventilation, hysteria, and epilepsy.

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