Orthostatic Hypotension Definition and Symptoms

This condition is not a disease entity itself, but a manisfestation in normal Blood Pressure regulation. The definition of Orthostatic Hypotension is an excessive fall in blood preassure on assuming the erect position. On arising to the erect position there is normally considerable pooling of blood in the dependent venous capacitance vessels. The subsequent transient decrease in venous return and cardiac output results in a reduction of blood pressure, which sensed by the baroreceptor mechanisms of the aortic and carotid sinus area. Autonomic reflexes result in rapid restoration of systolic blood pressure to normal, a slight overshoot in diastolic, pressure, and tachycardia.

These changes are primarily mediated through increased sympathetic discharge resulting in augmented vasomotor tone of the capacitance veins and an increase in myocardial rate and contractile force to enhance cardiac output. Peripheral arterial tone is also increased by similar mechanisms. 

Orthostatic Hypotension Etiology

The most common cause of symptomatic orthostatic hypotension is the cause of drugs that impair autonomic reflexes. Vasodilator therapy for hypertension usually is not associated with a greater blood pressure reduction in the standing position since autonomic reflexes remain intact, and the use of diuretics is associated with significant orthostatic hypotension only drugs (phentolamine and phenoxybenzamine, indicated only for hypertension due to pheochromocytoma, may also produce orthostatic hypotension.

Several groups of drugs used in nervous and mental disorders reduce blood pressure in the standing position as an important side effect. Monoamine oxidase inhibitors that used in depression may also reduce blood pressure with symptoms of orthostatic hypotension. Less commonly the tricyclic antidepressants may reduce blood pressure in standing position, additional drugs that may occasionally cause orthostatic hypotension include barbiturates and alcohol.

Acute or semi-acute severe reduction in intravascular volume may result in moderate to severe orthostatic hypotension due to the decrease in cardiac output despite intact autonomic reflexes. Acute hemorrhage, severe vomiting, diarrhea, excessive use of diuretics all may lead to marked volume contraction, dehydration, and orthostatic hypotension unless there is adequate fluid and electrolyte replacement.Similarly, adrenocortical insufficiency may lead to hypovolemic orthostatic hypotension in the absence of adequate salt intake.

Neuropathic disorders may interrupt the sympathetic reflex arc at one of several sites with consequent impairment of the normal adrenergic responses to standing. Diseases commonly associated with orthostatic hypotension are diabetes mellitus, porphyria, tabes dorsalis, pernicious anemia, uremia, and parkinson's syndrome. Surgical sympathectomy in the treatment of severe hypertension, vasospastic disorders, or peripheral vascular insufficiency also reduce in reduction of blood pressure in the standing position.

Symptoms

Mild to moderate acute reductions in cerebral blood flow may resut in a feeling of faint less, lightheadedness, and mental or visual blurring, and more severe reductions produce sudden syncope and even generalized seizures. Many other phenomena may appear as a symptoms in orthostatic hypotension. The orthostatic hypotension symptoms usually relate to specific disorder causing the condition. The diagnosis is made on the basis of symptoms suggestive of hypotension and the demonstration of marked reduction in blood pressure in the standing position. A specific etiologic diagnosis based upon each patient's presenting circumstances.