Low blood pressure might seem desirable, and for some people, it causes no problems. However, for many people, abnormally low blood pressure (hypotension) can cause dizziness and fainting. In severe cases, low blood pressure can be life-threatening.
A blood pressure reading lower than 90 millimeters of mercury (mm Hg) for the top number (systolic) or 60 mm Hg for the bottom number (diastolic) is generally considered low blood pressure.
The causes of low blood pressure can range from dehydration to serious medical disorders. It's important to find out what's causing your low blood pressure so that it can be treated.
For some people, low blood pressure signals an underlying problem, especially when it drops suddenly or is accompanied by signs and symptoms such as:
Extreme hypotension can result in this life-threatening condition. Signs and symptoms include:
If you have signs or symptoms of shock, seek emergency medical help.
If you have consistently low blood pressure readings but feel fine, your doctor will likely just 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. Still, it's important to see your doctor if you have signs or symptoms of low blood pressure because they can point to more-serious problems. It can be helpful to keep a record of your symptoms, when they occur and what you're doing at the time.
Blood pressure is a measurement of the pressure in your arteries during the active and resting phases of each heartbeat.
Current guidelines identify normal blood pressure as lower than 120/80 mm Hg.
Blood pressure varies throughout the day, depending on:
Blood pressure is usually lowest at night and rises sharply on waking.
What's considered low blood pressure for you may be normal for someone else. Most doctors consider blood pressure too low only if it causes symptoms.
Some experts define low blood pressure as readings lower than 90 mm Hg systolic or 60 mm Hg diastolic. If either number is below that, your pressure is lower than normal.
A sudden fall in blood pressure can be dangerous. A change of just 20 mm Hg — a drop from 110 systolic to 90 mm Hg systolic, for example — can cause dizziness and fainting when the brain fails to receive enough blood. And big drops, such as those caused by uncontrolled bleeding, severe infections or allergic reactions, can be life-threatening.
Medical conditions that can cause low blood pressure include:
Some medications can cause low blood pressure, including:
Doctors often break down low blood pressure (hypotension) into categories, depending on the causes and other factors. Some types of low blood pressure include:
Low blood pressure on standing up (orthostatic or postural) hypotension). This is a sudden drop in blood pressure when you stand up from a sitting position or after lying down.
Gravity causes blood to pool in your legs when you stand. Ordinarily, your body compensates by increasing your heart rate and constricting blood vessels, thereby ensuring that enough blood returns to your brain.
But in people with orthostatic hypotension, this compensating mechanism fails and blood pressure falls, leading to dizziness, lightheadedness, blurred vision and even fainting.
Orthostatic hypotension can occur for various reasons, including dehydration, prolonged bed rest, pregnancy, diabetes, heart problems, burns, excessive heat, large varicose veins and certain neurological disorders.
A number of medications also can cause orthostatic hypotension, particularly drugs used to treat high blood pressure — diuretics, beta blockers, calcium channel blockers and angiotensin-converting enzyme (ACE) inhibitors — as well as antidepressants and drugs used to treat Parkinson's disease and erectile dysfunction.
Orthostatic hypotension is especially common in older adults, but it also affects young, otherwise healthy people who stand up suddenly after sitting with their legs crossed for long periods or after squatting for a time.
Low blood pressure after eating (postprandial hypotension). This drop in blood pressure occurs one to two hours after eating and affects mostly older adults.
Blood flows to your digestive tract after you eat. Ordinarily, your body increases your heart rate and constricts certain blood vessels to help maintain normal blood pressure. But in some people these mechanisms fail, leading to dizziness, faintness and falls.
Postprandial hypotension is more likely to affect people with high blood pressure or autonomic nervous system disorders such as Parkinson's disease.
Eating small, low-carbohydrate meals; drinking more water; and avoiding alcohol might help reduce symptoms.
Low blood pressure (hypotension) can occur in anyone, though certain types of low blood pressure are more common depending on your age or other factors:
Even moderate forms of low blood pressure can cause dizziness, weakness, fainting and a risk of injury from falls.
And severely low blood pressure can deprive your body of enough oxygen to carry out its functions, leading to damage to your heart and brain.
The goal in testing for low blood pressure is to find the cause. Besides taking your medical history, doing a physical exam and measuring your blood pressure, your doctor might recommend the following:
Electrocardiogram (ECG). During this painless, noninvasive test, soft, sticky patches (electrodes) are attached to the skin of your chest, arms and legs. The patches detect your heart's electrical signals while a machine records them on graph paper or displays them on a screen.
An ECG, which can be performed in your doctor's office, detects irregularities in your heart rhythm, structural problems 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 have had one in the past.
Tilt table test. If you have low blood pressure on standing or from faulty brain signals (neurally mediated hypotension), a tilt table test can evaluate 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.
Low blood pressure that either doesn't cause signs or symptoms or causes only mild symptoms rarely requires treatment.
If you have symptoms, treatment depends on the cause. For instance, when medication causes low blood pressure, treatment usually involves changing or stopping the medication or lowering the dose.
If it's not clear what's causing low blood pressure or no treatment exists, the goal is to raise your blood pressure and reduce signs and symptoms. Depending on your age, health and the type of low blood pressure you have, you can do this in several ways:
Use more salt. Experts usually recommend limiting 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.
Wear compression stockings. The elastic stockings commonly used to relieve the pain and swelling of varicose veins can help reduce the pooling of blood in your legs.
Some people tolerate elastic abdominal binders better than they do compression stockings.
Medications. Several medications can be used to treat low blood pressure that occurs when you stand up (orthostatic hypotension). For example, the drug fludrocortisone, which boosts your blood volume, is often used to treat this form of low blood pressure.
Doctors often use the drug midodrine (Orvaten) 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.
Depending on the reason for your low blood pressure, you might be able to reduce or prevent symptoms.
Pay attention to your body positions. Gently move from a prone or squatting to a standing position. Don't sit with your legs crossed.
If you begin to get symptoms while standing, cross your thighs in a scissors fashion and squeeze, or put one foot on a ledge or chair and lean as far forward as possible. These moves encourage blood flow from your legs to your heart.
Eat small, low-carb meals. To help prevent blood pressure from dropping sharply after meals, eat small portions several times a day and limit high-carbohydrate foods such as potatoes, rice, pasta and bread.
Your doctor also might recommend drinking one or two strong cups of caffeinated coffee or tea with breakfast. Don't drink caffeine throughout the day because you will become less sensitive to caffeine, and caffeine can cause dehydration.
No special preparations are necessary to have your blood pressure checked. Don't stop taking medications you think might affect your blood pressure without your doctor's advice.
Here's some information to help you get ready for your appointment.
Make a list of:
For low blood pressure, basic questions to ask your doctor include:
Don't hesitate to ask other questions.
Your doctor is likely to ask you questions, including:
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