Ischemia
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In medicine, ischemia (Greek ισχαιμία, isch- is restriction, hema or haema is blood) is a restriction in blood supply, generally due to factors in the blood vessels, with resultant damage or dysfunction of tissue.
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Mechanism
Rather than in hypoxia, a more general term denoting a shortage of oxygen, ischemia is an absolute or relative shortage of the blood supply to an organ. Relative shortage means the mismatch of blood supply (oxygen delivery) and blood request for adequate oxygenation of tissue.
Ischemia can also be described as inadequate flow of blood to a part of the body, caused by constriction or blockage of the blood vessels supplying it. Ischemia of heart muscle produces angina pectoris.1
This can be due to:
- atherosclerosis (lipid-laden placques obstructing the lumen of arteries)
- hypotension (low blood pressure, e.g. in sepsis, heart failure)
- thromboembolism (blood clots)
- outside compression of a blood vessel, e.g. by a tumor
- foreign bodies in the circulation (e.g. amniotic fluid in amniotic fluid embolism)
References
1. Oxford Reference: Concise Medical Dictionary (1990, 3rd ed.). Oxford University Press: Market House Books.
Consequences
As the carrier of oxygen (oxygen is mainly bound to hemoglobin) insufficient blood supply leads to hypoxic tissue (anoxic in case of no oxygen supply at all) with the consequence of necrosis which causes cell death.
Ischemia is a feature of heart diseases, transient ischemic attacks, cerebrovascular accidents, and peripheral artery occlusive disease.