The Process of Fainting

Loss of consciousness is interruption of one's awareness of self and surroundings. When loss of consciousness is temporary and recovers spontaneously it is referred to as fainting or syncope. Temporary loss of consciousness, or syncope, has been reported to account for 3 percent of patient visits to emergency departments. How does temporary loss of consciousness occur? Temporary loss of consciousness is a result of a temporary reduction in the blood flow (and, therefore, oxygen) to the brain. This can lead to lightheadedness or a "black out" episode of loss of consciousness. There are many conditions which can temporarily impair the brain's blood supply. What conditions cause temporary loss of consciousness? Temporary loss of consciousness can be caused by heart conditions and conditions that do not directly involve the heart. Temporary loss of consciousness is more commonly caused by conditions that do not directly involve the heart. These conditions include those caused by: 1) a shift in body position from lying or sitting to a more vertical position (postural hypotension); 2) dehydration; 3) blood pressure medications; 4) diseases of the nerves to the legs of the elderly; 5) diabetes; or 6) Parkinson's disease. A decreased total blood volume and/or poor tone of the nerves of the legs from these conditions causes a disproportionate distribution of the blood in the legs, instead of up to the brain, when standing. Other common non-heart causes of temporary loss of consciousness include fainting after blood is drawn or after certain situational events (situational syncope), such as after urination, defecating, or coughing. This occurs because of a reflex of the involuntary nervous system (vasovagal reaction) that leads to slowing of the heart rate and dilation of the blood vessels in the legs, thus lowering the blood pressure. The result is that less blood (therefore less oxygen) reaches the brain as it is directed to the legs. With situational syncope, patients often note nausea, sweating, or weakness just before the loss of consciousness occurs. The vasovagal reaction is also called a vasovagal attack. And situational syncope is also called vasovagal syncope, vasodepressor syncope, and Gower syndrome after Sir William Richard Gower (1845- 1915), a famous English neurologist. Brain stroke or "near-stroke" (transient ischemic attack [TIA]) and migraines can also lead to temporary loss of consciousness. Heart conditions that can cause temporary loss of consciousness include abnormal heart rhythms (heart beating too fast or too slow), abnormalities of the heart valves (aortic or pulmonic valve stenosis), elevated blood pressure in the arteries supplying blood to the lungs (pulmonary artery hypertension), tears in the aorta (aortic dissection), and widespread disease of the heart muscle (cardiomyopathy). Fainting, which is also called syncope, can be related to many different things. More than one thing may be the cause of fainting. Sometimes a specific cause for fainting can't be found. Fainting can happen when not enough oxygen flows through your blood and into your brain. You lose consciousness, or "pass out," for a very brief time -- just a few seconds or minutes. A sudden drop in your blood pressure can cause you to faint. Sometimes your heart rate and blood vessels can't react fast enough when your body's need for oxygen changes. This is very common among older people. It can happen when: * You stand up fast. * You work or play hard, especially if it's very hot. * You begin to breathe too fast (called hyperventilating). * You get very upset. Being upset can affect the nerves that control your blood pressure. * You're taking medicine for high blood pressure. Coughing, urinating and stretching can also get in the way of the flow of oxygen to the brain and may be a cause of fainting. If you faint once during one of these activities, it's probably not something to worry about. But if it happens more than once, you should tell your doctor about it. If you faint when you turn your head to the side, the bones in your neck may be pinching on one of the blood vessels that leads to your brain. If this happens to you, be sure to tell your doctor about it. A drop in your blood sugar may also cause you to faint. This can happen if you have diabetes, but it may also happen if you don't eat for a long time. Some prescription medicines can cause fainting. Be sure to talk to your doctor if you think your fainting may be related to a medicine you're taking. Alcohol, cocaine and marijuana can also cause fainting.