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Orthostatic Intolerance

Causes Problems for Most POTS Patients

Orthostatic intolerance is defined as the inability to tolerate upright position due to increased symptom load which is generally relieved by lying down. Many people without postural orthostatic tachycardia syndrome (POTS) feel orthostatic intolerance when they are sick with COVID or the flu – new symptoms appear when they stand up to head to the bathroom. POTS is a form of orthostatic intolerance.

Symptoms of Orthostatic Intolerance

Here are the symptoms of orthostatic intolerance that are common in people with POTS:


  • Fainting or near fainting
  • Lightheadedness
  • Brain fog – memory, reasoning, concentration
  • Visual difficulties
  • Headache


  • Tachycardia
  • Changes in blood pressure – hypertension or hypotension

Digestive System

  • Nausea
  • Abdominal pain


  • Fatigue
  • Weakness
  • Sweating
  • Shaking
  • Exercise intolerance

What Causes Orthostatic Intolerance?

Several factors related to blood flow in the body determine whether you develop orthostatic intolerance.

  • Blood volume. Normal for an adult is 4-6 liters of blood. Hypovolemia or low blood volume is common in people with POTS.
  • Skeletal and respiratory muscle pumps. The contraction of muscles in the legs and changes in pressure in the chest help the blood in the veins move back toward heart.
  • Autonomic nervous system. The sympathetic nervous system (fight, flight or freeze), in particular, helps to constrict blood vessels and return blood to the heart and brain. POTS is the most common form of dysautonomia, which is caused by a malfunction of the autonomic nervous system.

The autonomic nervous system helps control many involuntary bodily functions, including heart rate and blood pressure. These are controlled independently and can keep adequate blood flow to the heart and brain regardless of body position in healthy individuals. When the autonomic nervous system malfunctions, as it does in POTS, then blood flow toward the heart is decreased, causing an increase in both heart rate and force of contraction.

The sympathetic nervous system releases norepinephrine and epinephrine to increase both heart rate and blood pressure. In order to increase blood pressure, the blood vessels constrict, making their diameter smaller. When the blood volume, muscle pumps and autonomic nervous system are normal, orthostatic intolerance does not develop. But when blood flow to the heart and head decreases, then orthostatic intolerance can occur.

Normal vs. POTS: Sitting to Standing

When you move from sitting to standing, there is a change in the pull of gravity on your body. When you stand up, gravity pulls the blood in your body down toward your legs and feet and away from your heart and brain. The response of the body to this change of position differs based on blood volume, intact muscle pumps, and function of the autonomic nervous system.

Healthy person

  • Increase heart rate and constrict blood vessels to keep blood moving toward heart and brain
  • Heart rate may increase by 10-20 bpm NORMAL

Person with POTS

  • Low blood volume means that the pull of gravity decreases the blood flow to the heart and brain too much
  • The autonomic nervous system doesn’t react properly, which means that the blood vessels don’t constrict as they should. Many POTS patients develop blood pooling in their hands and feet (turning red or blue, especially after a shower).
  • The heart rate increases by 30-75 beats per minute to keep blood flowing to the heart and brain and more symptoms then begin to appear

We use this phenomenon to quickly and easily diagnose POTS: the standing test.

Standing Test

1. Lay on your back for 5 minutes and be as still as possible. While still laying down, take the pulse and write it down.

2. Stand up still as possible for 2 minutes without leaning or flexing leg muscles. Take the pulse while still standing.  If there is no significant change in pulse, continue standing up to 10 minutes, taking the pulse every 2 minutes.

If the heart rate is greater than 120 beats per minute at any point while standing, POTS might be indicated. For adults age > 19, an increase in heart rate of 30+ beats per minute may indicate POTS. For children and teens age <19, an increase in heart rate of 40+ beats per minute is consistent with POTS.

You can use the Stand Test for POTS app to track changes in heart rate during this test.  If you have an automatic blood pressure cuff at home, you can use it to monitor blood pressure and pulse for you. It is normal to have a decrease in blood pressure by up to 20/10 mmHg when standing.

Treatment options for Orthostatic Intolerance

  • Low blood volume
    • Increase salt and fluid consumption. Many people with POTS need 6-10 grams of salt in either pill form, or by salting their food. In addition, 2-3 liters of fluids is required to prevent dehydration.
    • Raise head of bed 4-12 inches using bricks or wood blocks.
    • IV fluids, if necessary.
  • Poor blood flow – not enough constriction of blood vessels
    • Physical counter maneuvers. Pumping your ankles or tightening the muscles in your legs about 10 times before you stand can help to reduce symptoms when you stand. 
    • Compression garments. Try abdominal compression, compression socks and/or gloves with 20-30 mm Hg of pressure.
    • Exercise. Research has shown that exercise can improve POTS symptoms better than beta blockers.  If tolerated, start slowly and add a minute or two every couple of days until you build up to 30 minutes of exercise five days a week. Recumbent exercise like swimming, rowing, or recumbent bikes are recommended as well as weight training and Pilates.  Avoid upright exercise in the early stages of your exercise. 
    • Medications that might be helpful
      • Midrodrine, a vasoconstrictor, increases blood pressure and decreases blood pooling
      • Mestinon, a cholinesterase inhibitor, increases acetylcholine in the synapse to increase parasympathetic nervous system activity
  • Increased sympathetic tone “hyperadrenergic” POTS
    • Relaxation techniques
    • Medications that might be helpful
      • Beta blockers – block receptors for norepinephrine (sympathetic NS) to decrease  both heart rate and force of contraction
      • Fludrocortisone (Florinef), a mineralocorticoid, helps the body increase blood volume by reabsorbing salt and water. Be aware that this medication can deplete potassium and magnesium, so taking a supplement like Thermotabs that has these minerals can be helpful.

Want to learn more? Listen to Episode 7 of The POTScast where Dr. Cathy Pederson discusses orthostatic intolerance.