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diminished tension; lowered blood pressure. A consistently low blood pressure (systolic pressure less than 100 mm of mercury) usually is no cause for concern. In fact, low blood pressure often is associated with long life. However, extremely low blood pressure may be a sign of a serious condition such as shock, massive hemorrhage, hypovolemia, or severe dehydration from nausea and vomiting. In shock there is a disproportion between the blood volume and the capacity of the circulatory system, resulting in greatly reduced blood pressure. Hypotension may also be associated with addison's disease or inadequate thyroid function, but in both cases the primary disease produces so many other symptoms that the hypotension is not a major focus for concern.
orthostatic hypotension (postural hypotension) a fall in blood pressure (usually defined as a 20 to 30 point change in pulse or blood pressure), associated with dizziness, syncope, and blurred vision, occurring when a person goes from lying down or sitting to standing; it can be acquired or idiopathic, transient or chronic, and may occur alone or secondary to a disorder of the central nervous system such as the shy-drager syndrome.
supine hypotension vena caval syndrome.
a fall in blood pressure that occurs when a pregnant woman is lying on her back. It is caused by impaired venous return that results from pressure of the gravid uterus on the vena cava. Also called vena caval syndrome.