Ischemia is a restriction in blood supply, generally caused by factors in the blood vessels, resulting in damaged or dysfunctional tissue. It may also be spelled ischaemia or ischæmia. It also refers to the local loss of blood supply to a tissue that is sometimes the result of narrowed blood vessels, thrombosis and embolism.
Ischemia is different from hypoxia, a more general term that generally describes a of lack of oxygen in the air being breathed. Ischemia is an absolute or relative shortage of the blood supply to an organ, i.e. a shortage of oxygen, glucose and other blood-borne fuels. A relative shortage means the the blood being supplied is inadequate to maintain tissue metabolism. Ischemia results in tissue damage because of a lack of oxygen and nutrients. Ultimately, this can cause severe damage because of the potential for a build-up of metabolic wastes.
Ischemia 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.
The heart, kidneys and brain are among the organs most quickly damaged by loss of blood flow for any period of time.