[Differential orthostatic dysregulation disorders diagnosis].

Orthostatic circulatory disorders are frequently the cause of orthostatic intolerance, syncope or dangerous falls. A sufficient therapy should be based on a differential diagnosis by means of an active standing test or a tilt-table test. Three typical pathological reactions of blood pressure and heart rate can be differentiated. The hypoadrenergic orthostatic hypotension is characterised by an immediate drop in blood pressure (systolic drop > 20 mmHg below base line within 3 min) with or without compensatory tachycardia. It is caused by peripheral or central sympathetic dysfunction. Tachycardia (> 30 beats per minute above base line within 10 min) without significant blood pressure drop but with a fall of cerebral blood flow indicates a postural tachycardia syndrome. In general, there is no further somatic dysfunction. Increased venous pooling is thought to be the assumed pathomechanism. A reflex mechanism evokes the neurocardiogenic syncope after a certain time of standing: sympathetic inhibition yields a strong blood pressure drop and vagal activation bradycardia. Proved therapies include use of the mineralocorticoide fludrocortison (hypoadrenergic orthostatic hypotension), of the alpha-agonist midodrin (postural tachycardia syndrome) and of beta-blockers (neurocardiogenic syncope).