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Orthostatic intolerance (OI) is the development of symptoms when standing upright which are relieved when reclining. There are many types of orthostatic intolerance. OI can be a subcategory of dysautonomia, a disorder of the autonomic nervous system〔(【引用サイトリンク】 publisher = National Dysautonomia Research Foundation (NDRF) )〕 occurring when an individual stands up.〔(Definition at Dorland's Illustrated Medical Dictionary ) Retrieved through web archive on 2008-10-09.〕 It affects more women than men (female-to-male ratio is at least 4:1), usually under the age of 35.〔(【引用サイトリンク】 publisher = Vanderbilt Medical Center )〕 Orthostatic intolerance occurs in humans because standing upright 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 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 caused by abnormalities in the interactions between blood volume control, the cardiovascular system, the nervous system and circulation control systems.〔 ==Triggers== Symptoms of OI are triggered by the following: * An upright posture for long periods of time (e.g. standing in line, standing in a shower, or even sitting at a desk). * A warm environment (such as in hot summer weather, a hot crowded room, a hot shower or bath, after exercise). * Emotionally stressful events (seeing blood or gory scenes, being scared or anxious). * Astronauts returning from space not yet re-adapted to gravity. * Extended bedrest〔 * Inadequate fluid and salt intake. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Orthostatic intolerance」の詳細全文を読む スポンサード リンク
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