An Overview of Low Blood Pressure

High blood pressure (hypertension) is a well-known medical condition that affects as many as 80 million Americans. Its opposite, low blood pressure (hypotension), may not be as much of a household name, but it's worth knowing more about because it can cause health problems, particularly when it occurs suddenly.

Why Is Low Blood Pressure Concerning?

Blood pressure is the pressure in your arteries, the thick-walled blood vessels that carry blood with oxygen from your lungs throughout the rest of your body.

Blood pressure is measured in millimeters of mercury (mm Hg) and your reading has two numbers:

  • The top number is the systolic blood pressure, which refers to the pressure created in the arteries with each heartbeat.
  • The bottom number is the diastolic blood pressure, or the pressure in the arteries when the heart is resting between each beat. 

It’s healthy to keep your blood pressure below 120/80 mm Hg. But when your blood pressure is below 90/60 mm Hg, it may not be high enough to deliver oxygenated blood to all of your organs, particularly vital organs like the brain. This is why hypotension is of such concern.

Your Body and Your Blood Pressure

The arteries have a muscular layer that responds to signals from nerve receptors throughout the body. These signals tell the arteries to expand or contract as needed to continue to deliver oxygen efficiently when and where you need it.

For example, when you stand suddenly or rise up after lying down, the nerve receptors in your body send signals through the central nervous system to your arteries, causing the muscles in the artery wall to contract and increase the blood pressure enough to deliver more oxygen to supply your brain.

 Your central nervous system also signals your heart to beat more rapidly in order to compensate for the change in your posture.

However, when the nervous system does not react quickly to compensate for the change in pressure, your blood may pool in the lower portions of the body. This can result in reduced blood flow to the brain, causing a feeling of dizziness or lightheadedness and a drop in your effective blood pressure, known as orthostatic or postural hypotension.

Neurally mediated low blood pressure can also occur when you stand for a long period of time without changing position.

In addition to reduced response in the central nervous system, plaque may build up in your arteries with aging, causing narrowed arteries that may further reduce blood flow to your heart and brain.

Autonomic neuropathy and peripheral neuropathy, which are characterized by nerve damage and can be caused by diseases like diabetes, also affect the body’s ability to regulate blood pressure, causing postural hypotension.

Common Causes of Low Blood Pressure

  • Dehydration, which can result from vomiting, diarrhea, and excessive sweating

  • Hemorrhage, which can overwhelm the ability of the body to compensate for reduced blood volume

  • Medications: In addition to high blood pressure medications, which can alter both arterial pressure and heart rate, nitrates used to treat chest pain, medications for erectile dysfunction, some antidepressants, and antipsychotic medications are known to cause low blood pressure. Medicines used to treat people with Parkinson’s disease are also associated with postural hypotension.

  • Hormonal problems, such as hypothyroidism or low blood sugar (hypoglycemia)

  • Heart failure, which results in ineffective pumping by the heart
  • Arrhythmias (irregular heart rhythms), which prevent the heart from generating adequate contractile strength
  • Liver disease
  • Pregnancy
  • Stress: Your blood pressure can also drop suddenly and cause fainting or lightheadedness in response to a significant emotional stress. In these cases, your central nervous system may be overwhelmed.
  • Sepsis, which is caused by overwhelming infection and the body’s immune response to it
  • Anaphylaxis, which is a severe allergic reaction that causes a sudden and potentially fatal drop in blood pressure. Common causes of anaphylactic reactions include shellfish, penicillin, and nuts. Epinephrine is used to constrict the arteries and increase blood pressure in people who are having an anaphylactic reaction.

Signs and Symptoms of Low Blood Pressure  

Whatever the cause, low blood pressure can result in lack of oxygen to the brain and to other parts of the body. If you have low blood pressure but don’t experience any of these symptoms, then your blood pressure is most likely not a problem. Signs and symptoms of low blood pressure include:

  • Lightheadedness or dizziness
  • Fainting (syncope)
  • Blurred vision
  • Difficulty concentrating
  • Cool, clammy, pale skin
  • Shallow, rapid breathing
  • Thirst and dehydration
  • Fatigue
  • Nausea

What Is the Treatment for Low Blood Pressure?

Since low blood pressure can be the result of many different conditions, treatment may be specific to the condition causing it. Here are some of the most common causes of low blood pressure with associated treatments:

  • Decreased blood volume: This can occur as a result of dehydration, or from blood loss due to trauma or internal bleeding. It is treated by volume replacement with fluids and sometimes with blood products.
  • Orthostatic or postural hypotension as a result of central nervous system conditions is more common as we age. In these cases, it’s important to look for a cause. This may require further testing. Until the cause of your postural hypotension is identified, it is important to avoid things that seem to provoke the problem, such as getting up suddenly from a seated or reclining position.
  • Medications that can result in hypotension include beta-blockers, calcium channel blockers, ACE inhibitors, and diuretics, which are all used to treat hypertension. Other drugs, including antidepressants, antipsychotics, and drugs for treatment of Parkinson’s disease, may be the cause. If you have recently started a new medication and have new onset of low blood pressure, your healthcare provider may reduce your dose, substitute another drug, or discontinue treatment. You may develop tolerance to the effect over a period of weeks.
  • Hormonal (endocrine) causes of low blood pressure include adrenal insufficiency, known as Addison’s disease; low thyroid activity (hypothyroidism); disease of the parathyroid glands; and low blood sugar. When you have an endocrine cause of hypotension, replacement of the missing hormone may be required. If your endocrine problem is the result of a tumor, there are a variety of options, depending upon the location and type of tumor.
  • Pregnancy can also cause low blood pressure. The blood pressure changes during pregnancy in a predictable way, depending upon how quickly the body's blood volume adapts to the needs of the fetus. However, pressure on the major blood vessels by the uterus can cause low blood pressure. When it does, a change in position is needed. Towards the end of pregnancy, it is helpful to recline on the left side, which reduces pressure on the blood vessels from the growing uterus and fetus.
  • Nutritional deficiencies, including iron deficiency, vitamin B12, and folate, can cause anemia, which can lead to low blood pressure. Replacement therapy will be helpful, but some people will need fluids or even blood transfusion.
  • Neurally-mediated low blood pressure refers to low blood pressure after standing for a long period of time or low blood pressure with syncope resulting from a sudden dramatic emotional event. Younger individuals are most often affected and the condition usually resolves quickly. 
  • Anaphylaxis is a severe allergic reaction that can be fatal. It can cause extremely low blood pressure, breathing problems, swelling in the throat, and hives. Common causes include penicillin allergy, peanut allergy, shellfish, and bee stings. Individuals who know they have a severe allergy should avoid the substance to which they have had a reaction, but they should also carry an EpiPen, which is a self-injector of the medication epinephrine. Epinephrine is also used to treat anaphylaxis in the emergency department.
  • Changes in your heart rhythm can result in low blood pressure and syncope. If this is the case, you may need an anti-arrhythmic medication or a pacemaker. To establish this diagnosis, your physician may order a 24-hour monitor for your, which you will wear in your home as you go through your daily activities.
  • Heart failure can cause low blood pressure in very severe cases. Heart failure is a progressive disease best managed by a cardiologist. There are medications that can increase the heart's pumping action, but some people may need a heart transplant.
  • Liver disease, including cirrhosis, can cause low blood pressure because the liver is not able to produce the proteins needed to keep fluid within the blood vessels. Cirrhosis is best managed by a gastroenterologist or hepatologist, who can prescribe medications to reduce the symptoms. Since cirrhosis is the end stage of liver disease, some individuals may require a liver transplant.
  • Septic shock is the result of an overwhelming infection and the body’s immune response. It can be caused by bacterial toxins in the bloodstream. In these cases, it is important to treat the infection, but supportive care—including intravenous (IV) fluid and medications to raise your blood pressure (vasopressors)—are sometimes required until you are on the way to recovery.

A Word From Verywell

If you experience episodes of dizziness or lightheadedness when you change position, you may have postural hypotension. If you have recently started a new medication, you should ask your doctor if it could be a factor. Be certain to remain well-hydrated when exercising vigorously in extreme temperatures and when affected by a gastrointestinal bug that can cause vomiting or diarrhea. If you are injured and feel dizzy, see a healthcare professional right away to see if you have experienced a significant drop in your blood volume. Low blood pressure is generally most significant when it occurs suddenly or when it is the result of another disease process.


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