Ischemia

Ischemia is inadequate blood flow to a tissue, limiting oxygen and nutrient delivery and waste removal. Its effects range from reversible dysfunction to tissue death, depending on severity and duration.

Tissue perfusion: The passage of blood through tissue capillaries to supply cells and remove waste. Ischemia begins when tissue perfusion falls below the level needed to sustain its cells.
Myocardial ischemia: Insufficient blood flow to the heart muscle, usually because of coronary artery disease. The heart illustrates how ischemia can cause pain, electrical instability, and impaired pumping.
Electrocardiography: Recording of the heart’s electrical activity from electrodes placed on the body. Electrocardiographic changes can reveal myocardial ischemia, though a normal tracing does not exclude it.
Hypoxia: A condition in which tissue oxygen availability is insufficient for normal cellular function. Ischemia can cause hypoxia, but hypoxia may also occur despite adequate blood flow.
Oxygen extraction fraction: The proportion of oxygen delivered in blood that tissues remove for metabolism. Tissues can initially compensate for reduced flow by extracting more oxygen from passing blood.
Cerebral ischemia: Insufficient blood flow to the brain, which can cause transient or lasting neurological dysfunction. Brain tissue is highly sensitive to interruptions in its blood supply.
Stress testing: A diagnostic procedure that assesses cardiovascular function during increased cardiac workload. Exercise or medication can expose coronary flow limits that are not evident at rest.
Anoxia: A complete or near-complete absence of oxygen in a tissue or environment. Ischemia usually reduces oxygen delivery rather than eliminating it entirely.
Anaerobic glycolysis: The breakdown of glucose to lactate without using oxygen as the final electron acceptor. When oxygen delivery drops, cells rely more heavily on this less efficient energy pathway.
Acute limb ischemia: A sudden reduction in blood flow to an arm or leg that threatens tissue viability. This rapidly developing form shows how ischemia can become a time-critical vascular emergency.

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