Orthostatic circulatory dysregulation - Clinical signs, pathophysiology and treatment

Orthostatic circulatory dysregulation is an important differential diagnosis of syncopes. Symptoms are induced by decreased cerebral blood flow, caused by pathological gravitational blood pooling in the lower part of the body. Three different forms of orthostatic dysregulation can be distinguished by head-up tilt-table test: 1) The hypoadrenergic dysregulation, also called orthostatic hypotension, is characterised by an immediate decrease in blood pressure during orthostatic stress. It can be associated with an impairment of autonomic cardiac control. 2) The hyperadrenergic dysregulation, also called postural tachycardia syndrome, is characterised by an excessive tachycardia in upright position. 3) The vasovagal dysregulation, also called neurocardiogenic syncope, is characterised by a sudden simultaneous decrease in blood pressure and heart rate during prolonged orthostatic stress. Causes of orthostatic dysregulation are different disturbances of the autonomic nervous system with an insufficient activation of sympathetic vasoconstrictor neurones. Typically, the postural tachycardia syndrome and the vasovagal syncope are isolated disorders without any additional symptoms. On the other hand, orthostatic hypotension is a symptom of different neurological disorders accompanied with autonomic failure. Non-neurological causes of orthostatic hypotension are structural heart and vessel diseases, endocrinological disorders and drug-induced decreases in blood pressure. Conservative and pharmacological options are available for symptomatic treatment of orthostatic dysregulation. All approaches focus on opposing pathological gravitational blood pooling in the lower part of the body by increasing either vasoconstriction or intravasal volume. A stepwise approach is recommended: First of all, conservative options come into operation like increased fluid or salt intake. If uneffective, drugs like flu-drocortisone and sympathomimetic agents should be prescribed. In a third step, drugs are combined.