WHAT IS LOW BLOOD PRESSURE

What is Low Blood Pressure?

First off, "low blood pressure" is not strictly defined. While high blood pressure has clear numerical definitions, low blood pressure is not defined by a universally accepted value. In the past, some attempts were made to standardize the meaning of "low blood pressure," but no official set of guidelines is currently supported by any medical authority.
Generally speaking, doctors sometimes refer to a blood pressure of 90/60 as a rough rule of thumb when evaluating patients because experience seems to show that this is the point at which symptoms tend to develop.

In general, if you have no history of medical problems and are not experiencing any symptoms, a low blood pressure reading is not cause for concern. If you discover on your own that your blood pressure is below 120/80, you should mention it to your doctor during your next visit but probably don’t need to schedule a special appointment unless you know that the low reading represents a significant change from your average blood pressure.

Is Low Blood Pressure Dangerous?

With very few exceptions, chronic blood pressure below 120/80 is not dangerous. Low blood pressure is usually considered dangerous only when it causes symptoms or results from sudden blood pressure decreases. In cases where the blood pressure drops suddenly, it isn’t actually the low blood pressure itself that causes the danger, but rather the sudden change from a higher value to a lower value. Sudden changes in blood pressure can cause interruptions in the blood supply to the heart, kidneys and brain, and will almost always be accompanied by distinctive symptoms. An example of this situation is orthostatic hypotension, where changes in body position (usually a change from sitting to standing) are accompanied by a rapid drop in blood pressure. Usually, sudden episodes of low blood pressure are a sign that something else might be wrong, and are typically an indication for a full medical workup.

There is some recent research that suggests chronic low blood pressure may be of unique importance in people who have underlying kidney disease. For these people, chronic low blood pressure appears to trigger a complicated cascade of events that can lead to blood vessel damage and may lead to a stroke. Because this data is relatively new, no clear blood pressure guidelines for these patients have yet been developed.


What are the Symptoms of Low Blood Pressure?

Unlike high blood pressure symptoms, which are poorly defined and often totally absent, low blood pressure has several classic, easily recognized symptoms. The development of symptoms is considered an indicator that a patient should be evaluated to discover the cause of the low blood pressure and to rule out any underlying problems. Generally, blood pressure must fall to a fairly low value before symptoms develop.

Clincally, the value most often associated with the development of symptoms is 90/60, though this varies from person to person. Situations where the blood pressure drops rapidly, rather than exists chronically at a low level, do not require the blood pressure to drop to 90/60 before symptoms develop. Instead, changes of about 20mmHg from baseline blood pressure have been shown to cause classic low blood pressure symptoms.

Classic symptoms of low blood pressure include:

•Dizziness, or feeling like you’re standing on a rocking boat
•Fainting
•Changes in mental status (difficulty concentrating, confusion) or a sense of "impending doom" or anxiety
•Changes in breathing patterns (fast, shallow breathing is common during an episode of low blood pressure)
•Nausea
•Suddenly feeling cold or clammy, or a rapid onset of pale skin
While all of these symptoms indicate that a visit to the doctor is needed, fainting or ongoing dizziness are especially alarming and warrant an immediate visit to either your own doctor or to the emergency room. If you experience fainting along with nausea, chest pain, or any type of weakness/numbness in your body, you should consult a doctor immediately. These symptoms may be indicators of stroke, heart attack, or dangerous problems with the nervous system.

What Causes Low Blood Pressure?

Many things can make your blood pressure too low. These range in severity from normal changes caused by pregnancy to dangerous underlying conditions, like heart problems or hormone disturbances. Some low blood pressure causes are simple cases of dehydration brought on by vomiting, intense exercise, or the overuse of diuretics. Some studies have shown that a dehydration-induced weight loss of 1 percent is enough to trigger dizziness, confusion, or other symptoms of low blood pressure.

One especially important cause of low blood pressure is orthostatic hypotension, which is sometimes referred to as postural hypotension. This happens when blood pressure drops rapidly during changes to body position--usually when changing from sitting to standing--inducing classic signs that the blood pressure is too low, like dizziness, blurry vision, and fainting.


Other important causes of low blood pressure include:

•Heart problems that cause low heart rate, diminished heart strength, or a decrease in the amount of blood supplied to the body
•Normal changes associated with the first and second trimesters of pregnancy
•Side effects from certain medications, especially diuretics or other high blood pressure medications, like beta blockers. Medicines used to treat erectile dysfunction and certain psychiatric disorders can also cause low blood pressure.
•Hormone problems such as adrenal insufficiency or thyroid disease (overactive or underactive thyroid)
•Problems with the nervous system--especially disorders of the autonomic nervous system, including POTS and vasovagal syncope--can cause low blood pressure after extended periods of standing.
•Deficiencies of essential nutrients, such as folic acid, can cause the number of red blood cells to decrease (anemia)
•Alterations in blood sugar, like those caused by diabetes
•Age: Some older patients, especially those with existing high blood pressure, can experience postprandial hypotension, where the blood pressure drops suddenly after eating a large meal
While most cases of low blood pressure are not considered medical problems, cases where the low blood pressure is accompanied by symptoms should always be evaluated by a physician. A complete medical workup will often be needed in order to rule out the possibility of an underlying disorder.