Idiopathic orthostatic intolerance and postural tachycardia syndromes

Upright posture imposes a substantial gravitational stress on the body, for which we are able to compensate, in large part because of the autonomic ne rvous system. Alteration in autonomic function, therefore, may lead to orth ostatic intolerance. On one extreme, patients with autonomic failure caused by degenerative loss of autonomic function are severely disabled by orthos tatic hypotension and may faint whenever they stand up. Fortunately, such p atients are relatively rare. On the other hand, disabling orthostatic intol erance can develop in otherwise normal young people. These patients can be severely impaired by symptoms of fatigue, tachycardia, and shortness of bre ath when they stand up. The actual incidence of this disorder is unknown, b ut these patients make up the largest group of patients referred to centers that specialize in autonomic disorders. We will review recent advances mad e in the understanding of this condition, potential pathophysiological mech anisms that contribute to orthostatic intolerance, therapeutic alternatives currently available for the management of these patients, and areas in whi ch more research is needed.