Orthostatic intolerance

Orthostatic intolerance is a form of low blood pressure that can cause dizziness.

Prevalence
Orthostatic intolerance is a common dysfunction in ME/CFS Estimates of the rate of orthostatic intolerance in Chronic Fatigue Syndrome and myalgic encephalomyelitis patients vary widely, with estimates as low as 50% to as high as 97% of patients.

Orthostatic intolerance is also commonly associated with fibromyalgia

Orthostatic intolerance is diagnosed by a tilt table test. It is part of the Institute of Medicine report's proposed diagnostic criteria for Systemic Exertion Intolerance Disease.

Postural orthostatic tachycardia
Postural orthostatic tachycardia syndrome (POTS) is one of a group of disorders that have orthostatic intolerance (OI) as their primary symptom. The primary symptom of OI is lightheadedness or fainting. In POTS, the 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.

Orthostatic hypotension
Also called postural hypotension, it is a form of sudden low blood pressure that occurs upon standing. It can often cause dizziness. it is defined as a fall in systolic blood pressure of at least 20 mm Hg or diastolic blood pressure of at least 10 mm Hg when a person assumes a standing position.

Neurally mediated hypotension
Also called neurally mediate syncope, in NMH, peripheral vasodilation cauases blood to pool in the extremities. It is associated with a decrease in blood pressure, and a slow or lowered heart rate upon standing.

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 * 2016, NIH gives $246,000 for study of oral rehydration in ME/CFS patients with orthostatic intolerance