Hypotension

Hypotension is abnormally low blood pressure. Normal blood pressure is a reading around 120/80 mmHg (mmHg = millimeters of mercury, a unit for measuring pressure). Hypotension is blood pressure that is lower than 90/60 mmHg.

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 (a medical emergency resulting from insufficient blood supply).

Symptoms

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, lightheaded 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 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.

Diagnosis

If a person is in shock, emergency action is required to find the cause and treat the shock. For other types of hypotension, the doctor may order the following tests:

• Tilt table test. This test is used if you have fainting spells for no known reason. You lie on a table that moves from a lying down to an upright position. The doctor checks your reactions to the change in position.
• Blood tests. These tests can show whether anemia (low red blood cell count) or low blood sugar is causing the hypotension.
• EKG (electrocardiogram). This test measures the rate and regularity of the heartbeat.
• Portable EKG monitoring. Wires are attached to your chest with sticky patches and connected to a small battery-operated recorder.
  • A Holter monitor records all the heart’s electrical activity for 24 hours.
  • An event monitor records selected periods of the heart’s electrical activity. You may use this monitor for 1-2 months. When you feel symptoms, you press a button and the device records the heart’s electrical activity. The information can be sent over the telephone to the doctor.
• Echocardiogram. This test uses sound waves to create a moving picture of your heart. Echocardiogram provides information about the size and shape of your heart and how well your heart chambers and valves are functioning.
• Stress Test. Some heart problems are easier to diagnose when your heart is working harder and beating faster than when it’s at rest. During stress testing, you exercise (or are given medicine if you are unable to exercise) to make your heart work harder and beat faster while heart tests are performed.
• Your doctor also may order two newer tests along with stress testing: magnetic resonance imaging (MRI) and positron emission tomography (PET) scanning of the heart.

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:

• Not drinking enough fluids
• Fever
• Vomiting
• Severe diarrhea
• Excessive sweating from strenuous exercise

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:

• Diuretics
• Calcium channel blockers
• Angiotensin-converting enzyme (ACE) inhibitors
• Angiotensin II receptor blockers
• Nitrates
• Beta blockers

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:

• Anemia (low red blood cell count).
• Heart conditions leading to heart failure, such as a heart attack or viral infection of the heart. These conditions reduce the heart’s ability to pump enough blood around the body.
• Heart valve disorders.
• Severe infections.
• Endocrine conditions, such as hypothyroidism (underactive thyroid), hyperthyroidism (overactive thyroid), Addison’s disease (adrenal insufficiency), low blood sugar, and diabetes.
• Disorders of the central nervous system, such as Parkinson disease, multiple systems atrophy (Shy-Drager syndrome), and amyloidosis.
• Pulmonary embolism (a sudden blockage in a lung artery).

Finally, other events or conditions that can contribute to orthostatic hypotension include:

• Being out in the heat for a long time
• Having to stay in bed for a long time because of a medical condition
• Being pregnant
• Getting older (the body doesn’t manage changes in blood pressure as well as it gets older)

Neurally Mediated Hypotension

Neurally mediated hypotension (NMH) occurs when the brain and heart don’t communicate with each other properly. For example, when a person stands for a long time, blood begins to pool in the legs. This causes the person’s blood pressure to drop. Instead of telling the brain that blood pressure is low, the body mistakenly tells the brain that blood pressure is high. In response, the brain slows the person’s heart rate, which makes the blood pressure drop even further, causing dizziness and other symptoms.

Severe Hypotension Associated With Shock

Severe hypotension associated with shock can be caused by many conditions or events. Some of these conditions and events also are causes of orthostatic hypotension. The difference in shock is that the blood pressure doesn’t return to normal by itself, and it is at dangerously low levels. Shock is a medical emergency that must be treated immediately.

Certain severe infections can cause shock. This is known as septic shock. This type of shock can occur when bacteria enter the bloodstream. The bacteria release a toxin (a poison) that leads to a dangerous drop in blood pressure.

Shock can be caused by a severe decrease in the amount of blood or fluids in the body. This is known as hypovolemic shock. Hypovolemic shock can happen as a result of:

• Major bleeding on the outside of the body (for example, from an injury)
• Major bleeding inside the body (for example, from a ruptured blood vessel)
• Significant loss of body fluids from severe burns
• Severe inflammation of the pancreas
• Severe diarrhea
• Severe kidney disease
• Excessive use of diuretics

A major decrease in the heart’s ability to pump blood can cause shock. This is known as cardiogenic shock. It can be caused by a heart attack, pulmonary embolism, or arrhythmia.

A sudden and extreme relaxation of the muscles of arteries, which leads to dilation (widening) of the arteries and a drop in blood pressure, can cause shock. This is known as vasodilatory shock. It can happen because of:

• Severe head injury
• Reaction to some medicines
• Liver failure
• Poisoning
• Severe allergic reaction (anaphylactic shock)

Reference:

National Heart, Lung, and Blood Institute, USA.