Hypotension is the clinical term for low blood pressure, which can mean inadequate blood flow to the heart, brain and other vital organs. Blood pressure is measured in millimeters of mercury (mm HG). For a healthy young adult, normal blood pressure is considered to be less than 140mm Hg over 90mm Hg. The first number -- in this case, 140 -- is systolic blood pressure, the pressure in the blood vessels when the heart contracts; the second number -- in this case, 90 -- is the pressure between contractions. In most healthy people, blood pressure remains above 90/60 (or, 90 over 60). However, blood pressure varies from person to person; what is considered borderline low for one person may be normal for another.
Chronic low blood pressure is almost never serious. But health problems occur when blood pressure drops suddenly and the brain is deprived of an adequate blood supply. This can lead to dizziness or lightheadedness. It most commonly occurs in someone who's rising from a prone or sitting position to a standing position. In such cases, it is known as postural hypotension, orthostatic hypotension or neurally mediated orthostatic hypotension. Clinically, postural hypotension is defined as a 20mm Hg-reduction in systolic blood pressure or a 10mm Hg-reduction in diastolic blood pressure within three minutes of standing.
Postural hypotension is considered a failure of the autonomic nervous system -- the part of the nervous system that controls involuntary vital actions, such as the heartbeat -- to react appropriately to sudden changes. When you stand up, some blood pools in your lower extremities. Uncorrected, this would cause your blood pressure to fall. However, normally your body compensates by sending messages to your heart to beat faster and to your blood vessels to constrict. This offsets the drop in blood pressure. If this does not happen, or happens too slowly, postural hypotension results.
The incidence of both low and high blood pressure normally increases with age, due in part to normal physiologic changes. In addition, blood flow in the brain declines with age, often as a result of plaque buildup in blood vessels. So the prevalence of postural hypotension also increases with age; an estimated 10 percent to 20 percent of elderly people have postural hypotension.
Symptoms of postural hypotension include:
Postural hypotension, particularly in the elderly, may increase the risk of falls, leading to the potential for bone fractures and other injuries.
Postural hypotension can happen to anyone for a variety of physiologic reasons, such as dehydration, lack of food, prolonged standing in the heat or being generally run down. It can also be influenced by genetic make-up, aging, medication, dietary and psychological factors, and acute triggers, such as infection and allergy.
Postural hypotension occurs most frequently in people who are taking drugs to control high blood pressure (hypertension). It can also be related to pregnancy, strong emotion, or diabetes. The elderly are particularly affected, especially those who have high blood pressure or autonomic nervous dysfunction. Postprandial (after meals) hypotension is estimated to affect up to one-third of elderly people and is a common cause of dizziness and falls after eating.
Several drugs are commonly associated with postural hypotension. These medications can be divided into two major categories:
Common causes of physiologic, or naturally occurring, postural hypotension include:
Common causes of pathologic postural hypotension (that which can be attributed to disease) include:
Less common causes include disorders such as amyloidosis (caused by deposits of a waxy substance called amyloid in the body), vitamin deficiencies, spinal cord injuries, and neuropathies associated with cancer, particularly lung cancer or pancreatic cancer.
Symptoms of dizziness and lightheadedness upon standing do not necessarily mean that you have postural hypotension. A wide range of underlying conditions may cause these symptoms. An accurate diagnosis must be based on repeated evaluation of blood pressure and pulse rate after you have been lying down for at least five minutes and then after you stand quietly for one minute and then for three minutes. A hypotensive response may be immediate or delayed. Prolonged standing or a tilt test may be needed to detect a delayed hypotensive response.
If you have an underlying medical problem that causes postural hypotension, seek treatment for the underlying condition. For many people, chronic physiologic postural hypotension can be effectively treated with diet and lifestyle changes. Initially, your doctor may counsel you to increase your blood pressure by making these simple changes:
If these measures don't alleviate the problem, you may need medication. Although a wide range of drugs (including phenylpropanolamine, ephedrine and the nonsteroidal antiinflammatory drugs indomethacin and ibuprofen) have been used to treat hypotension, many are not consistently effective.
The following medications have proven effective in treating postural hypotension:
To prevent postural hypotensive events, follow the guidelines described in the Treatment section.
Call Your Doctor If: