Vasopressor response to increased intracranial pressure

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Abstract
The vasopressor response caused by diffuse intracranial hypertension generally occurs when the intracranial pressure approaches or equals the systemic arterial pressure. Occasionally a slight to moderate diffuse increase in intracranial pressure will elicit a vasopressor response; although this is in part dependent upon the animal''s level of anesthesia, other unknown factors must also exist. Expansion of an extradural balloon ultimately causes transtentorial obstruction of communication of pressure from the supratentorial space to the posterior fossa, and concomitantly, a consistent fall in the vasopressor threshold. Intracerebral balloon injections of minute quantities of fluid can cause a vasopressor response with only moderate elevation of the intracranial pressure and full communication of this pressure throughout the craniospinal axis. It is unlikely that these injections displace the brainstem or cause medullary ischemia. Local pressure or ischemia within the cerebral hemispheres can produce a vasopressor response. This suggestion is supported by the fact that a vasopressor effect also can be produced by local pressure on the isolated spinal cord.