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What is postural orthostatic tachycardia syndrome (POTS)?

Postural orthostatic tachycardia syndrome (POTS) belongs to a group of disorders that have orthostatic intolerance (OI) as their primary symptom. OI describes a condition in which an excessively reduced volume of blood returns to the heart after an individual stands up from a lying down position. The primary symptom of OI is lightheadedness or fainting. In POTS, lightheadedness or fainting is also accompanied by a rapid increase in heartbeat of more than 30 beats per minute, or a heart rate that exceeds 120 beats per minute, within 10 minutes of rising. The faintness or lightheadedness is relieved when the patient lies down again. Anyone at any age can develop POTS, but the majority of individuals affected (between 75 and 80 percent) are women between the ages of 15 to 50 years of age. Some women report an increase in episodes of POTS just before their menstrual periods. POTS often begins after a pregnancy, major surgery, trauma, or a viral illness. It may make individuals unable to exercise because the activity brings on fainting spells or dizziness.
Doctors are not sure what causes the reduced return of blood to the heart that occurs in OI, or why the heart begins to beat so rapidly in POTS. The current thinking is that these symptoms are the result of abnormalities in the sympathetic nervous system (which is responsible for decreasing muscle tone and increasing heartbeat in reaction to situations of stress or emergency), or the parasympathetic nervous system (which does the opposite), or both.
This answer from the National Institute of Neurological Disorders and Stroke has been reviewed and/or edited by Dr. William D. Knopf.

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