Orthostatic Intolerance and Low Blood Pressure

Older man sitting down due to dizziness

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Orthostatic intolerance (OI) is an abnormal response to being upright that can cause dizziness, fainting, and other symptoms that go away when you're seated or lying down. Typically, symptoms arise when you first stand up and are often due to an abnormal drop in blood pressure.

Most people experience OI now and then when they stand up too fast and get a "head rush." In some people, though, the symptom comes on frequently and is part of an underlying condition.

The term "orthostatic" comes from "orthostasis," which literally means standing up.

Acute Orthostatic Intolerance

OI can be chronic or acute. A chronic condition is one that lasts for a long time, while acute means that it's short-lived, like a cold.

Just about everyone experiences acute OI episodes now and then. Common triggers include:

  • Standing up too fast
  • Standing with the knees locked for too long
  • Strenuous exercise
  • A warm environment
  • Drinking alcohol
  • Certain medications
  • Acute illness
  • Dehydration
  • Emotionally stressful event
  • Extended bed rest

Chronic Orthostatic Intolerance

People with chronic orthostatic intolerance due to an underlying medical issue may have symptoms on most or all days. Depending on how severe symptoms are, OI can be quite debilitating.

OI is often a feature of dysautonomia, which is a disorder of the autonomic nervous system. It's a common symptom of both fibromyalgia and chronic fatigue syndrome, which are classified as dysautonomias.

OI is often a symptom of other conditions as well, such as:

  • Postural orthostatic tachycardia syndrome (POTS), which involves chronic OI
  • Neurally mediated or vasovagal syncope (fainting)

Low blood volume, which can result from disease or heavy bleeding, can also lead to orthostatic intolerance.

Causes of Orthostatic Intolerance

Many cases of OI are believed to be linked to an abnormality involving blood pressure.

When you stand up, your blood pressure is supposed to increase in order to combat the effects of gravity and keep blood going to your brain.

When you experience OI, it's believed that the blood pressure drops and the heart rate increases. The abnormally low blood pressure briefly deprives your brain of blood and oxygen, causing lightheadedness and possibly fainting. This type of OI is often called orthostatic hypotension. (Hypotension means low blood pressure.)

In chronic fatigue syndrome, a 2011 study suggests that OI may be linked to a heart abnormality in which the left ventricle (one of the chambers of the heart) is smaller than normal. Because this disease involves dysautonomia (dysfunction of the autonomic nervous system), it's possible that multiple factors combine to cause OI in this condition, as well.

Other underlying mechanism s may involve problems with blood flow, heart rate, and/or cardiorespiratory regulation that stems from the brain.

Symptoms of Orthostatic Intolerance

OI may lead to more symptoms than dizziness and fainting, including:

  • Headache
  • Visual disturbances (e.g., seeing spots, flashing lights)
  • Blurry vision
  • Weakness
  • Confusion
  • Trembling
  • Sweating
  • Fatigue
  • Nausea
  • Problems with breathing or swallowing
  • Paleness of the face

If you get frequent episodes of OI, and especially if they come with other symptoms, talk to your doctor. It may be due to an underlying illness.

Diagnosing Orthostatic Intolerance

OI is difficult to diagnose. It manifests differently from person to person, and it's not enough to say "you have orthostatic intolerance." In order for the diagnosis to lead to proper treatment and management, your doctor has to figure out why.

One common tests are the tilt-table test, also called upright tilt testing. You lie on a special table while having your heart and blood pressure monitored, and the table changes your position from lying to standing.

Other tests include an assessment of your autonomic nervous system or vascular integrity.

Once it's established that you have OI, your doctor will look for underlying conditions that can cause it.

Treating Orthostatic Intolerance

Often, OI isn't specifically treated but improves due to the treatment of the underlying condition.

However, OI is still a problem or if no underlying condition can be found, your doctor may suggest medications and/or lifestyle changes. Common recommendations include:

  • Drinking more than 64 ounces of water every day, typically spaced out evenly throughout the day
  • Avoiding triggers (warm showers, prolonged sitting, etc.)
  • Increasing salt intake
  • Pressure garments that prevent blood pooling

If your OI is severe or you've fainted before, you may want to consider walking with a cane or other assistive device. You may also benefit from handrails on stairs and a bar in the shower. If heat is a trigger for your OI, bathing or using a shower stool may be a good idea.

Fall-related injuries are a possible complication and can be especially dangerous in the elderly or people with weak bones, such as from osteoporosis. According to a 2013 study, about 40% of people with OI will faint at least once.

Depending on what's determined to be causing your OI, your doctor may prescribe one or more medications. Different types of medication for OI include:

  • Those that increase blood volume (fludrocortisone, erythropoietin, hormonal contraception)
  • ACE inhibitors (pyridostigmine)
  • Vasoconstrictors (Ritalin, Dexedrine, pseudoephedrine, Prozac)

A Word From Verywell

OI can be debilitating and scary, but you don't have to live with the limitations it can impose. Talking to your doctor, committing to what could be a lengthy diagnostic process, following treatments, and making lifestyle adjustments can help you keep this symptom from controlling your life.

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Article Sources

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  1. Vincent A, McAllister SJ et al. A report of the autonomic symptom profile in patients with fibromyalgia. J Clin Rheumatol. 2014;20(2):106-8. doi:10.1097/RHU.0b013e3182a225dd

  2. Stewart JM. Common syndromes of orthostatic intolerance. Pediatrics. 2013 May;131(5):968-80. doi:10.1542/peds.2012-2610

  3. Garland EM, Celedonio JE, Raj SR. Postural tachycardia syndrome: beyond orthostatic intolerance. Curr Neurol Neurosci Rep. 2015;15(9):60. doi:10.1007/s11910-015-0583-8

  4. Lanier JB, Mote MB, Clay EC. Evaluation and management of orthostatic hypotension. Am Fam Physician. 2011;84(5):527-536.

  5. Miwa K. Variability of postural orthostatic tachycardia in patients with myalgic encephalomyelitis and orthostatic intolerance. Heart Vessels. 2016;31(9):1522-8. doi:10.1007/s00380-015-0744-3

  6. Miwa K, Fujita M. Small heart with low cardiac output for orthostatic intolerance in patients with chronic fatigue syndrome. Clin Cardiol. 2011;34(12):782-6. doi:10.1002/clc.20962

  7. Yun DJ, Choi HN, Oh GS. A case of postural orthostatic tachycardia syndrome associated with migraine and fibromyalgia. Korean J Pain. 2013;26(3):303-6. doi:10.3344/kjp.2013.26.3.303

  8. American Heart Association. Tilt-table test. Updated July 31, 2015.