Friday, August 01, 2008

Orthostatic intolerance

Orthostatic intolerance occurs in some humans while standing upright. This action is a fundamental stressor and requires rapid and effective circulatory and neurologic compensations to maintain blood pressure, cerebral blood flow, and consciousness. When a human stands, approximately 750 mL of thoracic blood is abruptly translocated downward. People who suffer from orthostatic intolerance - OI lack the basic mechanisms to compensate for this deficit. Changes in heart rate, blood pressure, and cerebral blood flow that produce OI "may be related to abnormalities in the interplay between blood volume control, the cardiovascular system, the autonomic nervous system and local circulatory mechanisms that regulate these basic physiological functions.

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