Ischaemia

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  • Ischaemia is the failure or reduction of arterial blood supply to an organ or tissue.

Causes

  • Arteriospasm
    • Arterial trauma
    • Ergotism
    • Other drug effects
  • Compression of arteries/ arterioles
    • Ligatures
    • Tourniquets
  • Thromboembolism
    • Vascular impaction by embolic fragments

Sequelae

  • Several factors determine the extent and consequences of arterial obstruction.
    1. Degree of occlusion
      • May be partial or complete.
    2. Rapidity of occlusion
      • May be sudden or gradual.
    3. Presence and extent of a collateral circulation, such as
      • Anastomoses
      • Whether end areterioles are functional or actual.
      • Efficient alternative arterial supplies.
    4. Vulnerability of tissues/ cells to ischemia.
      • For example, their oxygen dependency and metabolic rate.
        • E.g. neurones and cardiac myocytes are much more susceptible than fibrous tissue.
  • There are two possible scenarios in ischeamia, each with their own sequelae.
    1. Complete, sudden failure of blood supply
      • Unless there is a good alternative collateral supply, this results in necrosis of tissue.
        • Collateral supplies may be inadequate to compensate if the blockage is severe.
      • This focal type of lesion is known as infarction.
    2. Incomplete, gradual failure of blood supply
      • Results in “accommodation”.
        • Manifests as atrophy, sometimes with fibrosis, following cellular hypoxia.
          • Minimal fibrosis occurs if collateral/ alternative supplies are good.