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Orthostatic intolerance (OI) is a series of clinical symptoms that develop during long-term standing in the upright position,with clinical manifestations of frequent,recurrent,or persistent dizziness,fatigue,and heart palpitations with or without syncope.These symptoms are relieved after changing to the supine posture [1].OI includes vasovagal syncope (VVS),postural tachycardia syndrome,and autonomic nervous dysfunction [2].The pathogenesis underlying the vasovagal response (VVR) is not well-defined,but is considered to involve changes in the autonomic system and vascular dysfunction [2,3].