Orthostatic hypotension or postural hypotension is the finding of a persistent drop in blood pressure on standing, defined as a greater than 20 mmHg fall in systolic pressure and/or a 5 mmHg fall in diastolic pressure one minute after a change from the supine to the upright position. Normally there is a drop in blood pressure of lesser magnitude on standing but this is usually quickly compensated for by the baroreceptor reflex. To demonstrate orthostatic hypotension, it may be necessary
to measure blood pressure not only on immediate standing but also after two to ten minutes, since the fall may be delayed. Measuring blood pressure automatically on a tilt table is also helpful in diagnosing orthostatic hypotension.
Symptoms which may be associated with orthostatic hypotension include exercise-induced or postprandial light-headedness, transient visual loss, blackouts (syncope), and pain in a "coathanger" distribution across the shoulders. There may be supine hypertension and reversal of the normal circadian blood pressure rhythm (normally lower at night), with increased frequency of micturition at night. Other features of autonomic dysfunction may be present, including dry eyes and dry mouth (xerophthalmia, xerostomia), a tendency to constipation, and lack of penile erections.
Orthostatic hypotension may be found in:
- Pure autonomic neuropathy
- Neurodegenerative disorders, such as multiple system atrophy, Parkinson’s disease, dementia with Lewy bodies
- Other causes of autonomic neuropathy (e.g., Guillain-Barré syndrome, amyloidosis).
However, the most common cause of orthostatic hypotension in hospital practice is probably dehydration or overzealous treatment with antihypertensive or diuretic agents.
Treatments for pure autonomic failure encompass both nonpharmacological approaches (e.g., increased salt intake, head-up bed tilt, wearing a G-suit) and pharmacological therapies, including fludrocortisone, ephedrine, and midodrine.
Mathias CJ, Kimber JR. Treatment of postural hypotension. Journalof Neurology, Neurosurgery and Psychiatry 1998; 65: 285-289