Ischemia

In medicine, ischemia (Greekισχαιμία, 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. It may also be spelled ischaemia or ischæmia.

Mechanism

Rather than in hypoxia, a more general term denoting a shortage of oxygen, ischæmia 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.

Ischæmia can also be described as an 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.

This can be due to:

• Tachycardia(abnormally rapid beating of the heart)
• Atherosclerosis(lipid-laden placques obstructing the lumen of arteries)
• Hypotension(low blood pressure, e.g. in septic shock, heart failure)
• Thromboembolism(blood clots)
• Outside compression of a blood vessel, e.g. by a tumor
• Foreign bodies in the circulation (e.g. amniotic fluidin amniotic fluid embolism)
• Sickle cell disease(abnormally shaped hemoglobin)

Consequences

Since oxygen is mainly bound to hemoglobinin red blood cells, insufficient blood supply causes tissue to become hypoxic, or, if no oxygen is supplied at all, anoxic. This can cause necrosisand cell death.

Ischemia is a feature of heart diseases, transient ischemic attacks, cerebrovascular accidents, ruptured arteriovenous malformations, and peripheral artery occlusive disease.

Tissues especially sensitive to inadequate blood supply are the heart, the kidneys, and the brain. Ischemia in brain tissue, for example due to strokeor head injury, causes a process called the ischemic cascadeto be unleashed, in which proteolyticenzymes, reactive oxygen species, and other harmful chemicals damage and may ultimately kill brain tissue.

References

1. Oxford Reference: Concise Medical Dictionary (1990, 3rd ed.). Oxford University Press: Market House Books.

See also

• Infarction
• Ischemic cascade

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It uses material from the http://en.wikipedia.org/wiki/Ischemia Wikipedia article Ischemia.