Source:http://linkedlifedata.com/resource/umls/id/C1299624
MSH: A syndrome of ORTHOSTATIC INTOLERANCE combined with excessive upright TACHYCARDIA, and usually without associated ORTHOSTATIC HYPOTENSION. All variants have in common an excessively reduced venous return to the heart (central HYPOVOLEMIA) while upright.,NCI: A syndrome characterized by orthostatic intolerance resulting in tachycardia, often accompanied by a decrease in the blood pressure. It occurs when individuals change from the supine position to an upright position. Other signs and symptoms include lightheadedness, fainting, fatigue and muscle weakness.