Low blood pressure, also called hypotension, would seem to be something to strive for. However, for many people, low blood pressure can cause symptoms of dizziness and fainting or mean that they have serious heart, endocrine or neurological disorders. Severely low blood pressure can deprive the brain and other vital organs of oxygen and nutrients, leading to a life-threatening condition called shock. Although blood pressure varies from person to person, a blood pressure reading of 90 millimeters of mercury (mm Hg) or less systolic blood pressure (the top number in a blood pressure reading) or 60 mm Hg or less diastolic blood pressure (the bottom number) is generally considered low blood pressure. The causes of low blood pressure can range from dehydration to problems with the way your brain signals your heart to pump blood. Low blood pressure is treatable, but it's important to find out what's causing your condition so that it can be properly treated.

Alternative Names of Hypotension are: Low Blood Pressure.

Complications of Hypotension

Even moderate forms of low blood pressure can cause not only dizziness and weakness but also fainting and a risk of injury from falls. And severely low blood pressure from any cause can deprive your body of enough oxygen to carry out its normal functions, leading to damage to your heart and brain.

Causes of Hypotension

Conditions that can cause low blood pressure

Some medical conditions can cause low blood pressure. These include:

• Pregnancy. Because a woman's circulatory system expands rapidly during pregnancy, blood pressure is likely to drop. During the first 24 weeks of pregnancy, systolic pressure commonly drops by five to 10 points and diastolic pressure by as much as 10 to 15 points. This is normal, and blood pressure usually returns to your pre-pregnancy level after you've given birth.
• Heart problems. Some heart conditions that can lead to low blood pressure include extremely low heart rate (bradycardia), heart valve problems, heart attack and heart failure. These conditions may cause low blood pressure because they prevent your body from being able to circulate enough blood.
• Endocrine problems. An underactive thyroid (hypothyroidism) or overactive thyroid (hyperthyroidism) can cause low blood pressure. In addition, other conditions, such as adrenal insufficiency (Addison's disease), low blood sugar (hypoglycemia) and, in some cases, diabetes, can trigger low blood pressure.
• Dehydration. When you become dehydrated, your body loses more water than it takes in. Even mild dehydration can cause weakness, dizziness and fatigue. Fever, vomiting, severe diarrhea, overuse of diuretics and strenuous exercise can all lead to dehydration.

Far more serious is hypovolemic shock, a life-threatening complication of dehydration. It occurs when low blood volume causes a sudden drop in blood pressure and a reduction in the amount of oxygen reaching your tissues. If untreated, severe hypovolemic shock can cause death within a few minutes or hours.

• Blood loss. Losing a lot of blood from a major injury or internal bleeding reduces the amount of blood in your body, leading to a severe drop in blood pressure.
• Severe infection (septicemia). Septicemia can happen when an infection in the body enters the bloodstream. These conditions can lead to a life-threatening drop in blood pressure called septic shock.
• Severe allergic reaction (anaphylaxis). Anaphylaxis is a severe and potentially life-threatening allergic reaction. Common triggers of anaphylaxis include foods, certain medications, insect venoms and latex. Anaphylaxis can cause breathing problems, hives, itching, a swollen throat and a drop in blood pressure.
• Lack of nutrients in your diet. A lack of the vitamins B-12 and folate can cause anemia, a condition in which your body doesn't produce enough red blood cells, causing low blood pressure.

Medications that can cause low blood pressure

Some medications you may take can also cause low blood pressure, including:

• Diuretics (water pills)
• Alpha blockers
• Beta blockers
• Drugs for Parkinson's disease
• Certain types of antidepressants (tricyclic antidepressants)
• Sildenafil (Viagra), particularly in combination with another heart medication, nitroglycerine

Signs & Symptoms of Hypotension

For some people, low blood pressure can signal an underlying problem, especially when it drops suddenly or is accompanied by signs and symptoms such as:

• Dizziness or lightheadedness
• Fainting (syncope)
• Lack of concentration
• Blurred vision
• Nausea
• Cold, clammy, pale skin
• Rapid, shallow breathing
• Fatigue
• Depression
• Thirst

Diagnosis of Hypotension

The goal in testing for low blood pressure is to find the underlying cause. This helps determine the correct treatment and identify any heart, brain or nervous system problems that may cause lower than normal readings. To reach a diagnosis, your doctor may recommend one or more of the following tests:

• Blood pressure test. Blood pressure is measured with an inflatable arm cuff and a pressure-measuring gauge. A blood pressure reading, given in millimeters of mercury (mm Hg), has two numbers. The first, or upper, number measures the pressure in your arteries when your heart beats (systolic pressure). The second, or lower, number measures the pressure in your arteries between beats (diastolic pressure).
• Blood tests. These can provide information about your overall health as well as whether you have low blood sugar (hypoglycemia), high blood sugar (hyperglycemia or diabetes) or a low number of red blood cells (anemia), all of which can cause lower than normal blood pressure.
• Electrocardiogram (ECG). This noninvasive test, which can be performed in your doctor's office, detects irregularities in your heart rhythm, structural abnormalities in your heart, and problems with the supply of blood and oxygen to your heart muscle. It can also tell if you're having a heart attack or if you've had a heart attack in the past.

Sometimes, heart rhythm abnormalities come and go, and an ECG won't find any problems. If this happens, you may be asked to wear a 24-hour Holter monitor to record your heart's electrical activity as you go about your daily routine.

• Echocardiogram. This noninvasive exam, which includes an ultrasound of your chest, shows detailed images of your heart's structure and function. Ultrasound waves are transmitted, and their echoes are recorded with a device called a transducer that's held outside your body. A computer uses the information from the transducer to create moving images on a video monitor.
• Stress test. Some heart problems that can cause low blood pressure are easier to diagnose when your heart is working harder than when it's at rest. During a stress test, you'll exercise, such as walking on a treadmill. You may be given medication to make your heart work harder if you're unable to exercise. When your heart is working harder, your heart will be monitored with electrocardiography or echocardiography. Your blood pressure also may be monitored.
• Valsalva maneuver. This noninvasive test checks the functioning of your autonomic nervous system by analyzing your heart rate and blood pressure after several cycles of a type of deep breathing: You take a deep breath and then force the air out through your lips, as if you were trying to blow up a stiff balloon.
• Tilt table test. If you have low blood pressure on standing, or from faulty brain signals (neutrally mediated hypotension), your doctor may suggest a tilt table test, which evaluates how your body reacts to changes in position. During the test, you lie on a table that's tilted to raise the upper part of your body, which simulates the movement from horizontal to a standing position.

Treatments of Hypotension

Low blood pressure that either doesn't cause signs or symptoms, or causes only mild symptoms, such as brief episodes of dizziness when standing, rarely requires treatment. If you have symptoms, the best treatment depends on the underlying cause, and doctors usually try to address the primary health problem — dehydration, heart failure, diabetes or hypothyroidism, for example — rather than the low blood pressure itself. When low blood pressure is caused by medications, treatment usually involves changing the dose of the medication or stopping it entirely.

If it's not clear what's causing low blood pressure or no effective treatment exists, the goal is to raise your blood pressure and reduce signs and symptoms. Depending on your age, health status and the type of low blood pressure you have, you can do this in several ways:

• Use more salt. Experts usually recommend limiting the amount of salt in your diet because sodium can raise blood pressure, sometimes dramatically. For people with low blood pressure, that can be a good thing. But because excess sodium can lead to heart failure, especially in older adults, it's important to check with your doctor before increasing the salt in your diet.
• Drink more water. Although nearly everyone can benefit from drinking enough water, this is especially true if you have low blood pressure. Fluids increase blood volume and help prevent dehydration, both of which are important in treating hypotension.
• Wear compression stockings. The same elastic stockings commonly used to relieve the pain and swelling of varicose veins may help reduce the pooling of blood in your legs.
• Medications. Several medications, either used alone or together, can be used to treat low blood pressure that occurs when you stand up (orthostatic hypotension). For example, the drug fludrocortisone is often used to treat this form of low blood pressure. This drug helps boost your blood volume, which raises blood pressure. Doctors often use the drug midodrine to raise standing blood pressure levels in people with chronic orthostatic hypotension. It works by restricting the ability of your blood vessels to expand, which raises blood pressure.

When to seek Medical Advice

In many instances, low blood pressure isn't serious. If you have consistently low readings but feel fine, your doctor is likely to monitor you during routine exams. Even occasional dizziness or lightheadedness may be a relatively minor problem — the result of mild dehydration from too much time in the sun or a hot tub, for example. In these situations, it's not a matter so much of how far, but of how quickly, your blood pressure drops. Still, it's important to see your doctor if you experience any signs or symptoms of hypotension because they sometimes can point to more serious problems. It can be helpful to keep a record of your symptoms, when they occur and what you were doing at the time.