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The Cushing reaction is a physiologic response to increased intracranial pressure.
When hydrostatic pressure of cerebrospinal fluid rises, it compresses the cerebral arterioles and diminishes blood supply to the brain, a condition known as ischemia. Central chemoreceptors in the brain sense the ischemia and respond with a swift and potent activation of the sympathetic nervous system in an attempt to raise blood pressure and restore perfusion. Although heart rate initially increases, the main effect of the sympathetic activity is a dramatic vasoconstriction in the systemic and peripheral arteries. The resultant sudden increase in blood pressure can cause a seemingly paradoxical parasympathetic response, leading to bradycardia.
- See also: Cerebral blood flow and CNS ischemic response
