How does fainting work?!
Question:
How does fainting work?
Today we dissected fetal pigs in Biology, and somebody fainted. That got me wondering what exactly goes on that makes people suddenly fall unconsious. It it a chemical in the brain, or the brain shuts down, or what? And what exactly triggers it?
Answers:
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) 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).