What is orthostatic hypotension?
Orthostatic (postural) hypotension is an excessive fall in BP when an upright position is assumed. The consensus definition is a drop of > 20 mm Hg systolic, 10 mm Hg diastolic, or both.
Normally, the gravitational stress of suddenly standing causes blood (½ to 1 L) to pool in the capacitance veins of the legs and trunk. The subsequent transient decrease in venous return reduces cardiac output and thus BP. In response, baroreceptors in the aortic arch and carotid bodies activate autonomic reflexes to rapidly return BP to normal. The sympathetic system increases heart rate and contractility and increases vasomotor tone of the capacitance vessels. Simultaneous parasympathetic (vagal) inhibition also increases heart rate. In most people, changes in BP and heart rate upon standing are minimal and transient, and symptoms do not occur. Homeostatic mechanisms may be inadequate to restore low BP if afferent, central, or efferent portions of the autonomic reflex arc are impaired by disorders or drugs, if myocardial contractility or vascular responsiveness is depressed, if hypovolemia is present, or if hormonal responses are faulty.
Symptoms include faintness, light-headedness, dizziness, confusion, or blurred vision occur within seconds to a few minutes of standing. This may resolve rapidly upon lying down. Some patients experience falls, syncope, or even generalized seizures.
Common causes of acute orthostatic hypotension
- Drugs (diuretics, beta blockers, nitrates, etc.)
- Prolonged bed rest
- Adrenal insufficiency
Common causes of chronic orthostatic hypotension
- Age-related changes in BP regulation
- Autonomic dysfunction
Treatment of orthostatic hypotension varies by cause. A few recommendations include:
- Increased fluid intake
- Limit alcohol use
- Discontinue suspected medications
- Slowly rising from a supine or sitting position.
- Apply compression stockings
- Raise the head of your bed
- Avoid prolonged standing
As an alternative, medications may be prescribed to treat orthostatic hypotension. Common medications include midrodrine and fludrocortisone. Both drugs restore normal blood pressure by vasoconstricting and increasing blood volume, respectively.
Lanier, J., Mote, M., Clay, E. 2011. Evaluation and Management of Orthostatic Hypotension. American Family Physician. 84(5): 527-536.