Even though some people faint for seemingly harmless reasons, such as the sight of blood, there are several potential causes. This temporary loss of consciousness that lasts no more than a few minutes can occur any time the brain isn't getting enough oxygen-rich blood.

What you need to know about the most common causes of syncope (pronounced "SIN ko PEE"), the medical term for fainting…

  • Heart conditions. Arrhythmias, in which the heart beats too fast (tachycardia), too slow (bradycardia) or in an irregular pattern, cause fainting in up to 12% of older adults who suffer from syncope. With an arrhythmia, ineffective pumping of blood can result in an insufficient amount of blood going to the brain.

Typical treatment: Medication to help control the underlying heart condition.

  • Medications. Certain drugs, such as medications for high blood pressure, heart failure, depression and Parkinson's disease, can cause fainting, especially when you first start taking them and/or if the dosage is too high. Men who take excessive doses of medication for an enlarged prostate, such as tamsulosin (Flomax), also may faint.

Typical treatment: Your doctor may lower the dosage or prescribe a different medication. Never stop taking a prescription drug without speaking to your physician.

  • Orthostatic (postural) hypotension (low blood pressure). Sitting or lying down causes blood to pool in the legs. When you stand, blood vessels normally constrict in response to this postural change, ensuring that your brain continues to get enough blood. But in people with orthostatic hypotension, this mechanism is defective.

Typical treatment: Drinking enough water (which increases blood volume and prevents dehydration)...avoiding alcohol (which is dehydrating).. and wearing support hose (to prevent blood from pooling in the legs). Some people may be prescribed fludrocortisone (Florinef) to increase blood volume (including that to the brain) and midodrine (ProAmitine) to constrict blood vessels.

  • Postprandial hypotension. After a meal (postprandial), blood pools in the intestines, thus reducing blood flow to the brain. In healthy people, the body responds by increasing heart rate and constricting blood vessels to maintain normal blood pressure. This mechanism fails in people with postprandial hypotension.

Typical treatment: Eat smaller, more frequent meals with fewer carbohydrates.

  • Vasovagal syncope. This type of fainting, which can be triggered by emotional distress, exertion (such as straining on the toilet), heat or the sight of blood, leads to an exaggerated bodily process. The heart rate slows and blood vessels in the legs widen, allowing blood to pool in the legs. This lowers blood pressure, reduces blood flow to the brain and can result in fainting.

In some people, vasovagal syncope results from overly sensitive reflexes involved in swallowing, urinating or defecating. Vasovagal syncope also can occur in people who have a condition known as carotid sinus hypersensitivity, which causes fainting when excess pressure is placed on the carotid (neck) artery-for example, when a shirt collar is too tight.

Typical treatment: Avoiding situations that trigger vasovagal syncope. In people with swallowing syncope, eating smaller, more frequent meals can help. Men should sit on the toilet while urinating if they have this form of syncope. Adding more fiber to your diet helps prevent constipation.

  • Illnesses. People with anemia may be more prone to fainting if they bleed excessively (due to an injury, for example), because blood loss can trigger a sharp drop in blood pressure. Hypoglycemia (low blood sugar), which can occur in people with or without diabetes, also can lead to fainting.

Typical treatment: People who have anemia should see their doctors regularly for treatment and monitoring of the condition. People with diabetes should control their blood sugar levels.

Identifying The Cause

Syncope is sometimes misattributed to a stroke, brain tumor or seizure-all of which can cause loss of consciousness. But strokes, tumors and seizures are more apt to also cause slurred speech and/or vision loss. According to a recent study, doctors often rush to perform costly heart tests, such as cardiac enzyme tests, which measure possible heart damage, while overlooking much less expensive postural blood pressure testing.

Simple test: When assuming a standing position after lying down, you may have orthostatic hypotension if systolic (top number) blood pressure drops by more than 20 points or if systolic pressure drops below 100.

Another important tool: The tilt table test. For this test, you lie down and are strapped to a table, which is then tilted to raise the upper body to simulate what happens when you go from a lying to a standing position. Your body's response to the change in position may indicate whether you have orthostatic hypotension.

The tilt table test may be used in addition to postural blood pressure testing (mentioned above).

If your doctor suspects that your fainting is due to a heart problem, you may receive an electrocardiogram (which measures electrical activity of the heart) and an echocardiogram a type of ultrasound test that helps detect abnormalities in heart rate or rhythm).

If You or Someone Else Faints

If you're feeling faint, lie or sit down immediately. If you're sitting, put your head between your knees to help restore blood flow to your brain. If someone else faints...

  • Get the person into a supine position (lying down with the face up). Raise the legs so they're higher than the head to bring blood back to the heart and head
  • Check the person's breathing. If breathing has stopped, call 911 and perform cardiopulmonary resuscitation (CPR)-about 100 uninterrupted chest compressions per minute.

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