Ischaemia
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ischemia definition causes symptoms American Heart Association
Ischaemia is inadequate blood flow to a tissue or organ, so it receives too little oxygen and nutrients and cannot clear metabolic waste properly. If severe or prolonged, it can cause irreversible cell injury and tissue death (infarction).
Common causes
- Arterial narrowing from atherosclerosis
- Blood clot forming locally or traveling from elsewhere
- Arterial spasm
- External compression of a vessel
- Severe low blood pressure or shock
- Increased tissue demand exceeding supply, such as during exertion in coronary artery disease
Examples
- Myocardial ischaemia: reduced blood supply to heart muscle, often causing angina. A complete prolonged blockage can cause myocardial infarction (heart attack).
- Cerebral ischaemia: reduced brain perfusion, causing transient ischaemic attack or ischaemic stroke.
- Acute limb ischaemia: sudden obstruction of limb blood flow.
- Mesenteric ischaemia: reduced intestinal blood supply.
Typical symptoms depend on site
- Heart: chest pressure, breathlessness, sweating, nausea. It can occasionally be silent, especially in people with diabetes.
- Brain: sudden facial droop, arm weakness, speech difficulty.
- Limb: sudden pain, pallor, coldness, numbness, weakness, and absent pulse.
- Gut: severe abdominal pain, sometimes out of proportion to examination findings.
Urgent emergency assessment is needed for sudden chest pain, stroke-like symptoms, a cold/painful numb limb, or severe sudden abdominal pain. The American Heart Association overview notes that ischaemic heart disease results from narrowed coronary arteries and may cause chest discomfort.
Difference between ischaemia and hypoxia
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hypoxia ischemia difference pathology oxygen blood flow
| Feature | Ischaemia | Hypoxia |
|---|---|---|
| Definition | Reduced or interrupted blood flow to a tissue | Reduced oxygen availability at the tissue level |
| Primary problem | Perfusion failure | Oxygen deficiency |
| Blood flow | Decreased | May be normal or decreased |
| Oxygen delivery | Reduced because less blood arrives | Reduced because blood has low oxygen content, low haemoglobin, poor perfusion, or cells cannot use oxygen |
| Nutrients and waste removal | Also impaired | Usually preserved if circulation remains intact |
| Severity | Usually more damaging | Often less damaging than ischaemia if blood flow is maintained |
Relationship
Ischaemia causes hypoxia, because insufficient blood reaches the tissue. But hypoxia can occur without ischaemia.
- Hypoxia without ischaemia: severe pneumonia, high altitude, anaemia, carbon monoxide poisoning, or cyanide poisoning. Blood flow may be normal, but oxygen delivery or use is impaired.
- Ischaemia with hypoxia: coronary artery blockage causing myocardial ischaemia. Blood flow is reduced, so oxygen, glucose, and other nutrients are not delivered, and waste products accumulate.
Why is ischaemia generally worse?
With isolated hypoxia, circulating blood can still deliver glucose and remove metabolic waste. During ischaemia, both oxygen and nutrient delivery fall and waste removal fails, so ATP depletion and cell injury occur more rapidly. Robbins describes ischaemia as hypoxia produced by reduced blood flow. Robbins, Cotran & Kumar Pathologic Basis of Disease, p. 50.
Memory aid:
- Hypoxia = low O₂
- Ischaemia = low blood flow, therefore usually low O₂ plus impaired nutrient supply and waste removal.
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