/huy'peuh ten"sheuhn/, n. Pathol.1. decreased or lowered blood pressure.2. a disease or condition characterized by this symptom. Also called low blood pressure.[1890-95; HYPO- + TENSION]
* * *Condition in which blood pressure is abnormally low.It may result from reduced blood volume (e.g., from heavy bleeding or plasma loss after severe burns) or increased blood-vessel capacity (e.g., in syncope). Orthostatic hypotensiondrop in blood pressure on standingresults from failure of the reflexes that contract muscles and constrict blood vessels in the legs to offset gravity as one rises. Hypotension is also a factor in poliomyelitis, shock, and barbiturate poisoning.
* * *also called low blood pressurecondition in which the blood pressure is abnormally low, either because of reduced blood volume or because of increased blood-vessel capacity. Though not in itself an indication of ill health, it often accompanies disease.Extensive bleeding is an obvious cause of reduced blood volume that leads to hypotension. There are other possible causes. A person who has suffered an extensive burn loses blood plasma—blood minus the red and white blood cells and the platelets. Blood volume is reduced in a number of conditions involving loss of salt and water from the tissues—as in excessive sweating and diarrhea—and its replacement with water from the blood. Loss of water from the blood to the tissues may result from exposure to cold temperatures. Also, a person who remains standing for as long as one-half hour may temporarily lose as much as 15 percent of the blood water into the tissues of the legs.Orthostatic hypotension—low blood pressure upon standing up—seems to stem from a failure in the autonomic nervous system. Normally, when a person stands up, there is a reflex constriction of the small arteries and veins to offset the effects of gravity. Hypotension from an increase in the capacity of the blood vessels is a factor in fainting (see syncope). Hypotension is also a factor in poliomyelitis (polio), in shock, and in overdose of depressant drugs, such as barbiturates (barbiturate).
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