Orthostatic Hypotension
Orthostatic hypotension is an excessive decrease in blood pressure that occurs when a person stands up, resulting in reduced blood flow to the brain and dizziness or fainting.
Orthostatic hypotension is particularly common among older people.
Orthostatic hypotension is not a specific disease but an inability to compensate quickly for changes in blood pressure. When a person stands up suddenly, gravity causes about a pint of blood to pool in the veins of the legs and lower body. As a result, the amount of blood returned to the heart and pumped out by the heart is reduced, and blood pressure falls. Normally, the body quickly responds to a decrease in blood pressure: The heart beats faster and more forcefully to increase its output of blood and the arterioles constrict to increase resistance to blood flow (see Section 3, Chapter 23). If these compensatory mechanisms malfunction or function too slowly--both of which commonly occur in older people--orthostatic hypotension may occur.
Causes
Orthostatic hypotension is caused by conditions that interfere with the compensatory mechanisms that control blood pressure. These conditions include many disorders and drugs as well as normal age-related changes.
Some conditions cause orthostatic hypotension by affecting the heart's ability to increase its output enough when a person stands. This problem can be caused by heart disease, such as abnormal heart rhythms and heart valve disorders. Also, with aging, the body becomes less able to increase the heart rate (and thus the heart's output) when a person stands.
Some conditions cause orthostatic hypotension by reducing blood volume. Diuretics, which are used to treat high blood pressure, can reduce blood volume by removing fluid from the body. Diuretics, especially potent ones given in high doses, are a common cause of orthostatic hypotension. Other causes of reduced blood volume include bleeding and an excessive loss of fluid due to severe vomiting, diarrhea, excessive sweating, or excessive urination (which is a common symptom of untreated diabetes or Addison's disease). Among older people, dehydration during an illness is a common cause of low blood volume leading to orthostatic hypotension. People who are ill may not be able to obtain fluids without assistance. Also, during an illness, the leg muscles are not used regularly. As a result, blood pools in the leg veins and is not pumped back to the heart (see Section 3, Chapter 36). Because this pooling reduces the amount of blood returning to the heart, it, in effect, reduces blood volume and thus reduces blood pressure.
Some conditions cause orthostatic hypotension by dilating arterioles and veins. Drugs that dilate arterioles (vasodilators) can cause orthostatic hypotension. They include nitrates, calcium channel blockers, angiotensin-converting enzyme (ACE) inhibitors, angiotensin II receptor blockers, alpha blockers, alcohol, and antidepressants. Disorders such as diabetes, amyloidosis, and spinal cord injuries may damage the nerves that regulate blood vessel diameter. In addition, veins dilate when body temperature increases, for example because of a warm day, a warm room, or too much clothing. Fever also has this effect.
Fatigue, exercise (which causes blood vessels to dilate), or consumption of a heavy meal (which requires increased blood flow to the intestines) can contribute to orthostatic hypotension.
Symptoms and Diagnosis
Most people with orthostatic hypotension experience some faintness, light-headedness, dizziness, confusion, or blurred vision when they get out of bed abruptly or stand up after sitting for a long time. Symptoms are worse if people are tired, have been exercising, have consumed alcohol, or have eaten a heavy meal. A severe decrease in blood flow to the brain can cause the person to faint and even to have convulsions.
These symptoms suggest orthostatic hypotension. The diagnosis can be confirmed if the blood pressure falls significantly when the person stands and returns to normal when the person lies down. Doctors then look for the cause of orthostatic hypotension, because treatment and prognosis depend on the cause.
Treatment
Even when the cause of orthostatic hypotension cannot be treated, certain measures can often reduce or eliminate symptoms. For example, susceptible people should not sit or stand up rapidly or remain standing still for long periods. They should sit or stand up slowly. Wearing fitted elastic stockings up to the waist may help reduce pooling of blood in the leg veins. If orthostatic hypotension results from prolonged bed rest, gradually increasing the time spent sitting up each day may help.
Several measures help maintain blood volume. People with orthostatic hypotension should drink plenty of fluids and little or no alcohol. People who do not have heart failure or high blood pressure are often told to salt their food liberally or to take salt tablets. However, a doctor's supervision is necessary, because a high-salt diet can lead to heart failure (see Section 3, Chapter 25), particularly in older people. For people who have severe symptoms, taking hormones that cause salt to be retained, such as fludrocortisone, can increase blood volume. However, use of such hormones increases the risk of heart failure, particularly for older people and for people who have heart disease. Use of fludrocortisone can also cause a loss of potassium, so taking a potassium supplement may be necessary. Midodrine may be taken with fludrocortisone to help prevent blood pressure from falling. Midodrine constricts arterioles, thereby reducing their capacity to hold blood and increasing resistance to blood flow.
If these measures are ineffective, other drugs (such as pindolol, dihydroergotamine, ibuprofen, and clonidine), which work in various ways, may help relieve orthostatic hypotension. However, the risk of side effects from these drugs may make their use undesirable, particularly by older people.
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