An Overview of Low Blood Pressure

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Low blood pressure (called hypotension) is the point at which a person's blood pressure has dropped so low that the heart can no longer deliver an adequate supply of blood to their body. Because our bodies are all different, the actual point can vary from one person to the next.

Many factors can cause low blood pressure. It may be due to an underlying health condition, like anemia or a heart problem, or be due to external factors, like dehydration or the side effect of a medication.

When diagnosing low blood pressure and its underlying culprit, besides measuring your blood pressure, your doctor will also access your symptoms and perform a physical examination and/or other tests.

In order to ease the symptoms of low blood pressure, the underlying problem needs to be treated (e.g., fluids for dehydration). Less commonly, medications to raise a person's blood pressure are required.

Symptoms

Generally speaking, the lower your blood pressure is, the better. That said, when blood pressure drops so low that blood flow to organs is compromised, troubling symptoms will develop that require medical attention. These symptoms may include one or more of the following:

  • Lightheadedness or dizziness
  • Blurry vision
  • Weakness
  • Fatigue
  • Nausea
  • Heart palpitations
  • Headache
  • Difficulty concentrating
  • Fast, shallow breathing

Complications

Low blood pressure is usually most serious when it results in a prolonged reduction in the blood flow to critical organs. Within minutes, a reduced blood supply to the heart or brain can result in irreversible damage. Chronically low (or even borderline low) blood pressure can have an adverse effect on the kidneys as well.

If the drop is sudden and severe, people will often describe a feeling of "impending doom." In rare instances, a dramatic drop can lead to syncope (fainting), shock, coma, and even death.

Types and Causes

There are three main types of low blood pressure—orthostatic hypotension, severe hypotension linked to shock, and neurally mediated hypotension.

Orthostatic Hypotension

Orthostatic hypotension, which is sometimes referred to as postural hypotension, occurs when a person's blood pressure drops rapidly when going from a lying or sitting position to standing.

Under normal circumstances, when you go from lying or sitting to standing up, your brain responds by telling the muscles in the walls of your arteries to contract. This contraction narrows the arteries and increases your blood pressure. Your brain also sends signals to your heart to pump faster, so there is more blood flow to stabilize your blood pressure.

When these signals go awry, though, blood pools in the lower portion of your body. This blood pooling results in lower blood pressure and less blood reaching the brain.

There are certain conditions that increase a person's chances for developing orthostatic hypotension, such as:

Orthostatic hypotension may also be a side effect from certain medications, especially diuretics or other high blood pressure medications, like beta-blockers. Medicines used to treat erectile dysfunction, and certain antidepressants can also cause low blood pressure.

You may also experience orthostatic hypotension simply by drinking alcohol, being out in the heat, or being immobile for a long period.

Severe Hypotension Related to Shock

While some of the causes of severe hypotension in shock may also cause orthostatic hypotension, in shock, the drop is much more severe and doesn't return to normal.

The causes of hypotensive shock include:

  • Major blood loss (internal or external)
  • Septic shock from infection or toxins
  • Severe fluid loss from diarrhea, burns, or overuse of diuretics
  • Cardiogenic shock due to a heart attack, arrhythmia, or pulmonary embolism
  • Vasodilatory shock, which may be seen with a head injury, liver failure, poisoning, or anaphylaxis.

Neurally Mediated Hypotension

Another type of low blood pressure is called neurally mediated hypotension. This type of low blood pressure occurs after extended periods of standing and is most common in young people. Emotional stress can be a trigger of neurally mediated hypotension. 

Diagnosis

Hypotension can be diagnosed by using a blood pressure cuff. The cuff measure both the systolic pressure (the pressure exerted in your blood vessels when your heart beats) and the diastolic pressure (the pressure in your blood vessels when your heart rests between beats).

The reading is described by the systolic pressure over the diastolic pressure, such as 120/80 (the borderline normal reading for adults in the United States).

While hypotension doesn't have an exact definition, many doctors consider 90/60 mmHg to be the cut-off point by which hypotension can be reasonably diagnosed. Unfortunately, this doesn't fully represent what low blood pressure really means.

For example, athletes in excellent physical shape may have a blood pressure of 85/50 and not be considered hypotensive. On the other hand, a person with coronary artery disease may be considered hypotensive with a blood pressure reading of 120/70.

Other Tests

To pinpoint the underlying cause, your doctor may order blood tests to check if you have anemia, hypothyroidism, low blood sugar, or another condition associated with hypotension.

An electrocardiogram (ECG) can be used to detect heartbeat irregularities, structural heart abnormalities, and problems with the supply of blood and oxygen to the heart muscle. Similarly, a type of ultrasound known as an echocardiogram can provide detailed images of your heart's structure and function.

A stress test, performed on a treadmill or stationary bike, can evaluate your heart during activity with either an ECG or echocardiogram.

A tilt table test can be used to assess changes in blood pressure at different angles and is useful in diagnosing orthostatic hypotension and neurally mediated hypotension.

Treatment

The treatment of hypotension is dependent on the underlying causes. Sometimes, medication is needed.

Address the Underlying Cause

Here are a few examples of how doctors treat the underlying "why" behind a patient's low blood pressure:

It is not uncommon for people prescribed high blood pressure medications to end up with blood pressure that is too low. A simple dose adjustment may be all that is needed to correct the condition.

To avoid "rebound hypertension" or other potentially serious side effects, be sure to not stop your high blood pressure medication on your own. Several high blood pressure medications require a period of weaning first before they can be stopped altogether.

If dehydration is the culprit behind a person's low blood pressure, increased fluid intake based in part on your body mass index (BMI) is the treatment. For example, a person with a normal BMI would likely only need eight to ten 8-ounce glasses of water per day to maintain ideal hydration. People with a high BMI may need far more.

Adding more salt to your diet may also aid in normalizing your blood pressure.

Compression socks may also help by forcing pooling blood in the legs back toward the core. This is a common treatment for people with heart failure and other circulatory disorders.

Medications

In some cases, medication may be prescribed to counteract physiological abnormalities that other interventions can't. These medications include Florinef (fludrocortisone), which boosts your blood volume, and Orvaten (midodrine) which restricts blood vessels and raises the blood pressure.

For more serious causes of low blood pressure, like shock, medications called vasopressors may be given to help raise the blood pressure. Vasopressors are usually administered in the intensive care unit and are given intravenously through a central line.

A Word From Verywell

Feeling a little woozy when you stand up suddenly is something most people experience occasionally. But if it happens frequently, it may be a concern. Moreover, if your low blood pressure is accompanied by symptoms such as dizziness, lightheadedness, fatigue, or fainting, you should talk with your doctor right away. Even if the symptoms seem "manageable," don't ignore them or try to live with them. Treatment is available.

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Article Sources

  1. American Heart Association. (2016). Low Blood Pressure - When Blood Pressure Is Too Low.

  2. Lanier JB, Mote MB, Clay EC. Evaluation and Management of Orthostatic Hypotension. Am Fam Physician. 2011 Sep 1;84(5):527-36.


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