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.