hypotension (low blood pressure)
Hypotension is abnormally low blood pressure. Normal blood pressure is a reading of less than 120/80 mmHg (mmHg = millimeters of mercury, a unit for measuring pressure). Hypotension is blood pressure that is lower than 90/60 mmHg. Compare with high blood pressure (hypertension).
Some people have low blood pressure all the time. They have no signs or symptoms and their low readings are normal for them. In other people, blood pressure drops below normal because of some event or medical condition. Hypotension is a medical concern only if it causes signs and/or symptoms such as dizziness, fainting, or, in extreme cases, shock.
The body is very sensitive to changes in blood pressure. Special cells in the arteries, called baroreceptors, can sense if blood pressure begins to rise or drop. When the baroreceptors sense a rise or drop in blood pressure, they cause certain responses to occur throughout the body in an attempt to bring the blood pressure back to normal.
For example, if you stand up quickly, the baroreceptors will sense a drop in your blood pressure. They quickly take action to make sure that blood continues to flow to the brain, kidneys, and other important organs. The baroreceptors cause the heart to beat faster and harder. They also cause the small arteries (arterioles) and veins (the vessels that carry blood back to the heart) to narrow.
Most forms of hypotension happen when the body can't bring blood pressure back to normal or can't do it fast enough.
Outlook
In a healthy person, hypotension without signs or symptoms is usually not a problem and requires no treatment. Doctors will want to identify and treat any underlying condition that is causing the hypotension, if one can be found. Hypotension can be dangerous if a person falls because of dizziness or fainting.
Shock, a severe form of hypotension, is a life-threatening condition that is often fatal if not treated immediately. Shock can be successfully treated if the cause can be found and the right treatment provided in time.
Types of hypotension
There are several types of hypotension. One type, chronic asymptomatic hypotension, happens in people who always have low blood pressure. They have no symptoms and need no treatment. Their low blood pressure is normal for them.
Other types of hypotension happen only sometimes, when blood pressure suddenly drops too low. The symptoms and effects on the body can be mild or severe. The three main types of this kind of hypotension are orthostatic hypotension, neurally mediated hypotension (NMH), and severe hypotension associated with shock.
Orthostatic hypotension
Orthostatic hypotension is low blood pressure that occurs upon standing up from a sitting or lying down position. It can cause a person to feel dizzy, light-headed or even to faint. It occurs when the body is not able to adjust blood pressure and blood flow fast enough for the change in position. Usually orthostatic hypotension lasts for only a few seconds or minutes after a person stands up. Sometimes a person will need to sit or lie down for a short time while the blood pressure returns to normal.
Orthostatic hypotension can occur in all age groups, but it is more common in older adults, especially those who are frail or in poor health. Orthostatic hypotension can be a symptom of other medical conditions, and treatment generally focuses on treating the underlying condition(s). Some people can have orthostatic hypotension but also have high blood pressure when lying down.
A form of orthostatic hypotension called postprandial hypotension is a sudden drop in blood pressure after a meal. Postprandial hypotension most commonly affects older adults. It also is more likely to affect those with high blood pressure or diseases such as Parkinson's disease.
Neurally mediated hypotension
In this form of hypotension, blood pressure drops after a person has been standing for a long time. A person may feel dizzy, faint, or sick to the stomach as a result. NMH also can happen when a person faces an unpleasant, upsetting, or frightening situation.
NMH affects children and young adults more often than other age groups. Children often outgrow this form of hypotension.
Severe hypotension associated with shock
Many times people will say a person has "gone into shock" as a result of an emotionally upsetting experience. But to doctors, the word "shock" has a different meaning. Shock is a life-threatening condition in which blood pressure drops so low that the brain, kidneys, and other vital organs can't get enough blood to work properly. It is different from the other forms of hypotension because blood pressure drops much lower, and it is life threatening if not treated immediately. There are many causes of shock, including major loss of blood, certain severe types of infection, severe burns, severe allergic reactions, and poisoning.
Causes
Hypotension is caused by conditions or events that interfere with the body's ability to control blood pressure.
Orthostatic hypotension
Orthostatic hypotension has many causes. Sometimes, two or more causes combined will result in hypotension.
Dehydration is the most common cause of orthostatic hypotension. Dehydration occurs when the body loses more water than it takes in. People can become dehydrated because of:
Some medicines used to treat high blood pressure and heart disease can make it more likely that a person will develop orthostatic hypotension. These medicines include:
Also, medicines used to treat certain other medical conditions, such as anxiety, depression, erectile dysfunction, and Parkinson disease, can make it more likely that a person will develop orthostatic hypotension.
Other substances that can contribute to orthostatic hypotension include alcohol, barbiturates, and some prescription and over-the-counter medicines, when taken in combination with high blood pressure medicines.
Certain medical conditions can increase a person's chances of having orthostatic hypotension. Some of these conditions are: