Hyperaemia

Active or Arterial Hyperaemia

• Increased arterial blood inflow to an organ or tissue.
• Causes erythema.
• Results from active dilatation of arterioles and capillaries in association with autonomic nervous stimulus.
• May be:
  • Physiological and transient.
  • Pathological and sustained.
    • Usually associated with inflammation.
      • The classic example being the weal reaction in man or "blistering" in animals.
    • May also occur where there is:
      • Exaggerated localised raised temperature.
      • Generalised pyrexia.
      • The presence of toxins.

Reaction hyperaemia

• May follow restoration of blood flow after a short-term occlusion.
  • For example, after a tourniquet or ligature is removed.
• Vessels dilate, as a result of local release of vaso-active substances.
  • There is also possibly a neurogenic component involved.