What is orthostatic hypotension?
When a person stands up from sitting or lying down, the body must work to adjust to that change in position. It is especially important for the body to push blood upward and supply the brain with oxygen. If the body fails to do this adequately, blood pressure falls, and a person may feel lightheaded or even pass out. Orthostatic hypotension is the term used to describe the fall in blood pressure when a person stands (orthostatic= upright posture of the body; hypo= less + tension=pressure).
Adequate blood supply to the body's organs depends upon three factors:
1. a heart strong enough to pump,
2. arteries and veins that are able to constrict or squeeze, and
3. enough blood and fluid within the vessels.
When the body changes position, a variety of actions occur involving all parts of the cardiovascular system as well as the autonomic nervous system that helps regulate their function.
The autonomic nervous system can be considered to "run in the background" of the body, regulating body processes that we take for granted. There is a balance between the sympathetic system (adrenergic nerves), that speed things up, and the parasympathetic system (cholinergic nerves) that slow things down. These names are based on the type of chemical that is used to transmit signals at the nerve endings.
- Adrenaline (from the sympathetic nervous system) allows the body to respond to stress. Imagine seeing a bear in the woods; your heart beats faster, your palms get sweaty, your eyes dilate, and your hair stands on end.
- Acetylcholine is the chemical that is the anti-adrenaline and is involved in the parasympathetic nervous system.
These two systems are in balance, and yet need to respond to routine changes in the body that happens throughout the day.
- When the body moves to a standing position, pressure monitors (baroreceptor cells) located in the carotid arteries and the aorta sense a subtle drop in blood pressure because of gravity, which causes blood to flow towards the legs.
- Almost immediately, the sympathetic system is stimulated, causing the heart rate to increase, the heart muscle to contract or squeeze more forcefully, and blood vessels to constrict or narrow.
- All of these actions serve to increase the blood pressure so that an adequate amount of blood can still be pumped to the brain and other organs.
- Without these changes, gravity would cause the blood to remain in the lowest part of the body and away from the brain, causing symptoms of lightheadedness or even passing out.
Orthostatic hypotension is not a disease or a complaint from an individual; it is an abnormal change in blood pressure and heart rate associated with an illness.
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| | 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 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 (small arteries) constrict to increase resistance to blood flow (see Low Blood Pressure: Introduction). If these compensatory mechanisms malfunction or function too slowly—both of which commonly occur in older people—orthostatic hypotension may occur. 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 Venous Disorders: Introduction). 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 intestine) can contribute to orthostatic hypotension. 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 seizures. 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. 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 in certain people, particularly 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 people who have heart disease. Use of fludrocortisone can also cause a loss of potassium, so taking a potassium supplement may be necessary. Midodrine Some Trade Names PROAMATINE may be taken with fludrocortisone to help prevent blood pressure from falling. Midodrine Some Trade Names PROAMATINE 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 and clonidine Some Trade Names CATAPRES ), which work in various ways, may help relieve orthostatic hypotension in certain people. However, the risk of side effects from these drugs may make their use undesirable, particularly by older people. |
