- A partial or complete loss of consciousness with interruption of awareness of oneself and ones surroundings. When the loss of consciousness is temporary and there is spontaneous recovery, it is referred to as syncope or, in nonmedical quarters, fainting. Syncope accounts for nearly one in every 30 visits to an emergency room. Syncope is due to a temporary reduction in blood flow and therefore a shortage of oxygen to the brain. This leads to lightheadedness or a "black out" episode, a loss of consciousness. Temporary impairment of the blood supply to the brain can be caused by heart conditions and by conditions that do not directly involve the heart: Non-cardiac causes: Syncope is most commonly caused by conditions that do not directly involve the heart. These conditions include: Postural hypotension: Drop in blood pressure due to changing body position to a more vertical position after lying or sitting; Dehydration causing a decrease in blood volume. Blood pressure medications leading to low blood pressure. Diseases of the nerves to the legs in older people (especially with diabetes or Parkinson's disease) when poor tone of the nerves of the legs draws blood into the legs from the brain. Brain stroke or "near-stroke" (transient ischemic attack). A migraine attack. Fainting after blood drawing or after certain situations like urinating, defecating or coughing (situational syncope) due to a reflex of the involuntary nervous system (called the vasovagal reaction) that slows the heart and dilates blood vessels in the legs in such cases people often feel nausea, sweating, or weakness just before losing fainting. Cardiac causes: Heart conditions that can cause syncope or fainting due to temporary loss of consciousness include: Abnormal heart rhythms (heart beating too fast or too slow). Abnormalities of the heart valves (aortic stenosis or pulmonic valve stenosis). High blood pressure in the arteries supplying the lungs (pulmonary artery hypertension). Tears in the aorta (aortic dissection). Widespread disease of the heart muscle (cardiomyopathy). To be sure, many of the causes of temporary loss of consciousness can be detected by a careful history. Dizziness after standing up in an older person suggests postural hypotension. Temporary loss of consciousness after urinating, defecating, or coughing suggests situational syncope. Cardiac causes of temporary loss of consciousness such as aortic stenosis or cardiomyopathy are suggested by the occurrence of the event during exercise. Signs of weakness localized to certain areas of the body with temporary loss of consciousness suggest stroke.
Medical dictionary. 2011.
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