Orthostatic intolerance (OI) is the development of symptoms whenstanding upright that are relieved whenreclining.[1] There are many types oforthostatic intolerance. OI can be a subcategory ofdysautonomia, a disorder of theautonomic nervous system[2] occurring when an individual stands up.[3] Some animal species with orthostatic hypotension have evolved to cope with orthostatic disturbances.[4][5]
A substantial overlap is seen betweensyndromes of orthostatic intolerance on the one hand, and eitherchronic fatigue syndrome orfibromyalgia on the other.[6] It affects more women than men (female-to-male ratio is at least 4:1), usually under the age of 35.[7] OI can also be a symptom ofmitochondrial cytopathy.[8]
Orthostatic intolerance occurs in humans because standing upright is a fundamentalstressor, so requires rapid and effectivecirculatory andneurologic compensations to maintainblood pressure,cerebral blood flow, andconsciousness. When a human stands, about 750 ml ofthoracic blood are abruptly translocated downward. People who have OI lack the basic mechanisms to compensate for this deficit.[1] Changes inheart rate, blood pressure, and cerebral blood flow that produce OI may be caused by abnormalities in the interactions betweenblood volume control, thecardiovascular system, thenervous system, andcirculation control system.[9]
Orthostatic intolerance can be classified asacute OI andchronic OI.[citation needed]
Patients who have acute OI usually manifest the disorder by a temporaryloss of consciousness andposture, with rapid recovery (simplefaints, orsyncope), as well as remaining conscious during their loss of posture. This is different from a syncope caused bycardiac problems because the triggers for the fainting spell (standing, heat,emotion) and identifiableprodromal symptoms (nausea, blurred vision, headache) are known. As Dr. Julian M. Stewart, an expert in OI fromNew York Medical College states, "Many syncopal patients have no intercurrent illness; between faints, they are well."[1]
Symptoms:[9]
A classic manifestation of acute OI is a soldier who faints after standing rigidly at attention for an extended period of time.
Patients with chronic orthostatic intolerance have symptoms on most or all days. Their symptoms may include most of the symptoms of acute OI, plus:
Symptoms of OI are triggered by:
Many patients go undiagnosed ormisdiagnosed and either untreated or treated for other disorders. Current tests for OI (tilt table test, NASA Lean Test,[13] adapted Autonomic Profile (aAP),[14]autonomic assessment, andvascular integrity) can also specify and simplify treatment.[9] Patients with dysautonomia symptoms can be referred to a cardiologist, neurologist, or even a gastroenterologist for treatment and management.[15][16]
Most patients experience an improvement of their symptoms, but for some, OI can be gravelydisabling and can be progressive in nature, particularly if it is caused by an underlying condition that is deteriorating. The ways in which symptoms present themselves vary greatly from patient to patient; as a result, individualized treatment plans are necessary.[17]
OI is treatedpharmacologically and non-pharmacologically. Treatment does not cure OI; rather, it controls symptoms.[citation needed]
Physicians who specialize in treating OI agree that the single most important treatment is drinking more than 2 liters (8 cups) of fluids each day. A steady, large supply of water or other fluids reduces most, and for some patients all, of the major symptoms of this condition. Typically, patients fare best when they drink a glass of water no less frequently than every two hours during the day, instead of drinking a large quantity of water at a single point in the day.[6]
For most severe cases and some milder cases, a combination ofmedications is used. Individual responses to different medications vary widely, and a drug that dramatically improves one patient's symptoms may make another patient's symptoms much worse. Medications focus on three main issues:[6]
Medications that increase blood volume:
Medications that inhibit acetylcholinesterase:
Medications that improve vasoconstriction:
Behavioral changes that patients with OI can make are:
A notable person with OI isGreg Page, founding member and originallead singer of the Australianchildren's music groupThe Wiggles. Due to being diagnosed with this illness, Page left the group in late 2006, and was replaced by his understudy,Sam Moran.[18][19] Two years later in late 2008, he went on to create his own fund for OI to help fund research into this then-little known disorder.[20] Page recovered enough to temporarily return to The Wiggles in early 2012 to help with the transition to the next generation of Wiggles, after which he again left the group at the end of 2012 and was replaced byEmma Watkins and again byTsehay Hawkins.[21]
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