Differential diagnosis of orthostatic dysregulation

Orthostatic circulatory disorders are frequently the cause of orthostatic i ntolerance, syncope or dangerous falls. A sufficient therapy should be base d on a differential diagnosis by means of an active standing test or a tilt -table test. Three typical pathological reactions of blood pressure and hea rt rate can be differentiated. The hypoadrenergic orthostatic hypotension i s 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. Tachycardi a (> 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 pos tural tachycardia syndrome,ln general, there is no further somatic dysfunct ion. 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 an d vagal activation bradycardia. Proved therapies include use of the mineral ocorticoide fludrocortison (hypoadrenergic orthostatic hypotension), of the alpha-agonist midodrin (postural tachycardia syndrome) and of beta-blocker s (neurocardiogenic syncope).