Lower than normal blood pressure due to a variety of causes
- Age, gender, genetics, and lifestyle as risk factors depend on the cause
Hypotension is the medical term for low blood pressure. The pressure with which the blood is pumped around the circulation varies between individuals and throughout the day. The normal range is that which is adequate to supply all of the organs and body tissues with blood. Blood pressure at the lower end of the normal range is not likely to produce symptoms. However, if the pressure in the circulation falls below the level needed to provide the brain with enough blood, light-headedness or fainting may occur.
A common type of hypotension is postural hypotension, in which suddenly standing or sitting up leads to light-headedness and fainting.
What are the causes?
In many people, low blood pressure occurs as a result of dehydration following loss of large amounts of fluid or salts from the body. For example, heavy sweating, loss of blood, or profuse diarrhoea may all cause hypotension.
Disorders that reduce the efficiency of the heart’s pumping action are common causes of low blood pressure. These disorders include heart failure (see Acute heart failure, and Chronic heart failure), heart attack (see Myocardial infarction), and an irregular heartbeat (see Arrhythmias).
Hypotension may also be caused by an abnormal widening of the blood vessels, which may occur as a result of an infection in the bloodstream (see Septicaemia) or a severe allergic reaction (see Anaphylaxis).
Postural hypotension may be caused by disorders in which the nerve supply to the blood vessels is damaged, such as diabetic neuropathy or peripheral neuropathies. Hypotension may also sometimes be the result of an adverse effect of certain drugs, particularly those used in the treatment of high blood pressure (see Antihypertensive drugs) and certain types of antidepressant drugs.
What are the symptoms?
You may not have symptoms of hypotension unless your blood pressure is very low. Symptoms may include:
Light-headedness and fainting.
These symptoms are usually temporary, and blood pressure rises when the cause is treated. However, if blood pressure is too low to provide an adequate blood supply to vital organs, it can be fatal (see Shock).
What might be done?
Your blood pressure will be measured while you are lying down and then standing (see Blood pressure measurement). There may be an obvious reason for your low blood pressure. For example, you may be dehydrated and need treatment with intravenous fluids. If your doctor suspects an underlying disorder, such as a heart condition, you may be admitted to hospital for tests and treatment. If your medication is causing hypotension, your doctor will probably advise a change of drug or dosage.
From the 2010 revision of the Complete Home Medical Guide © Dorling Kindersley Limited.
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