Editing Orthostatic intolerance (section)

{{Short description|Human disease}}
'''Orthostatic intolerance''' ('''OI''') is the development of symptoms when [[orthostasis|standing upright]] that are relieved when [[supine position|reclining]].<ref name="overview">{{cite web | title = Orthostatic Intolerance: An overview | author = Julian M. Stewart | publisher = [[WebMD]] | url = http://www.emedicine.com/ped/topic2860.htm | access-date = 2007-08-20}}</ref> There are many types of [[orthostatic]] intolerance.  OI can be a subcategory of [[dysautonomia]], a disorder of the [[autonomic nervous system]]<ref name="defintion">{{cite web | title = What is dysautonomia? | publisher = National Dysautonomia Research Foundation (NDRF) | url = http://www.ndrf.org/ | access-date = 2007-08-20}}</ref> occurring when an individual stands up.<ref>[https://web.archive.org/web/20080202064651/http://www.mercksource.com/pp/us/cns/cns_hl_dorlands.jspzQzpgzEzzSzppdocszSzuszSzcommonzSzdorlandszSzdorlandzSzdmd_i_11zPzhtm Definition at Dorland's Illustrated Medical Dictionary] Retrieved through web archive on 2008-10-09.</ref> Some animal species with orthostatic hypotension have evolved to cope with orthostatic disturbances.<ref>{{cite journal |last1=Lillywhite |first1=Harvey B. |title=Orthostatic Intolerance of Viperid Snakes |journal=Physiological Zoology |date=November 1993 |volume=66 |issue=6 |pages=1000–1014 |doi=10.1086/physzool.66.6.30163751 |jstor=30163751 |s2cid=88375293 }}</ref><ref>{{cite journal |last1=Nasoori |first1=Alireza |last2=Taghipour |first2=Ali |last3=Shahbazzadeh |first3=Delavar |last4=Aminirissehei |first4=Abdolhossein |last5=Moghaddam |first5=Sharif |title=Heart place and tail length evaluation in Naja oxiana, Macrovipera lebetina, and Montivipera latifii |journal=Asian Pacific Journal of Tropical Medicine |date=September 2014 |volume=7 |pages=S137–S142 |doi=10.1016/S1995-7645(14)60220-0 |pmid=25312108 |doi-access=free }}</ref>

A substantial overlap is seen between [[syndromes]] of orthostatic intolerance on the one hand, and either [[chronic fatigue syndrome]]  or [[fibromyalgia]]  on the other.<ref name="generalinfo">{{cite web|author=Peter C. Rowe|author-link=Peter Rowe (doctor)|title=General information brochure on Orthostatic Intolerance and its treatment|url=http://www.pediatricnetwork.org/medical/OI/johnshopkins.htm|url-status=live|archive-url=https://web.archive.org/web/20070728190350/http://www.pediatricnetwork.org/medical/OI/johnshopkins.htm <!-- Bot retrieved archive -->|archive-date=2007-07-28|access-date=2007-08-21|publisher=The Pediatric Network}}</ref>  It affects more women than men (female-to-male ratio is at least 4:1), usually under the age of 35.<ref name="vanderbilt">{{cite web | title = Vanderbilt autonomic dysfunction center | publisher = Vanderbilt Medical Center | url = http://www.mc.vanderbilt.edu/root/vumc.php?site=adc&doc=4788 | access-date = 2007-08-20 | archive-url = https://web.archive.org/web/20070808101106/http://www.mc.vanderbilt.edu/root/vumc.php?site=adc&doc=4788 | archive-date = 2007-08-08 | url-status = dead }}</ref> OI can also be a symptom of [[mitochondrial cytopathy]].<ref>{{Cite journal |last=Kanjwal |first=Khalil |last2=Karabin |first2=Beverly |last3=Kanjwal |first3=Yousuf |last4=Saeed |first4=Bilal |last5=Grubb |first5=Blair P. |date=October 2010 |title=Autonomic dysfunction presenting as orthostatic intolerance in patients suffering from mitochondrial cytopathy |url=https://pubmed.ncbi.nlm.nih.gov/20960537/ |journal=Clinical Cardiology |volume=33 |issue=10 |pages=626–629 |doi=10.1002/clc.20805 |issn=1932-8737 |pmc=6653231 |pmid=20960537}}</ref>

Orthostatic intolerance occurs in humans because standing upright is a fundamental [[stressor]], so requires rapid and effective [[circulatory]] and [[neurologic]] compensations to maintain [[blood pressure]], [[cerebral blood flow]], and [[consciousness]].  When a human stands, about 750 ml of [[thoracic]] blood are abruptly translocated downward.  People who have OI lack the basic mechanisms to compensate for this deficit.<ref name=overview/>  Changes in [[heart rate]], blood pressure, and cerebral blood flow that produce OI may be caused by abnormalities in the interactions between [[blood volume]] control, the [[cardiovascular system]], the [[nervous system]], and [[circulation control system]].<ref name=nymc/>