Definition of Hypotension:

Low blood pressure, or hypotension, occurs when blood pressure during and after each heartbeat is much lower than usual. This means the heart, brain, and other parts of the body do not get enough blood.

See also: Blood pressure

Causes, incidence, and risk factors:

Blood pressure that is borderline low for one person may be normal for another. The most important factor is how the blood pressure changes from the normal condition.

Most normal blood pressures fall in the range of 90/60 millimeters of mercury (mm Hg) to 130/80 mm Hg. But a significant drop, even as little as 20 mm Hg, can cause problems for some people.

There are three main types of hypotension:

• Orthostatic hypotension, including postprandial orthostatic hypotension
• Neurally mediated hypotension (NMH)
• Severe hypotension brought on by a sudden loss of blood (shock)

Orthostatic hypotension is brought on by a sudden change in body position, usually when shifting from lying down to standing. This type of hypotension usually lasts only a few seconds or minutes. If this type of hypotension occurs after eating, it is called postprandial orthostatic hypotension. This form most commonly affects older adults, those with high blood pressure, and persons with Parkinson's disease.

NMH most often affects young adults and children. It occurs when a person has been standing for a long time. Children usually outgrow this type of hypotension.

Low blood pressure is commonly caused by drugs such as:

• Alcohol
• Anti-anxiety medications
• Certain antidepressants
• Diuretics
• Heart medicines, including those used to treat high blood pressure and coronary heart disease
• Medications used for surgery
• Painkillers

Other causes of low blood pressure include:

• Advanced diabetes
• Anaphylaxis (a life-threatening allergic response)
• Changes in heart rhythm (arrhythmias)
• Dehydration
• Fainting
• Heart attack
• Heart failure
• Shock (from severe infection, stroke, anaphylaxis, major trauma, or heart attack)