Effects of increased arterial pressure on blood flow in the damaged brain.

The effect of induced arterial hypertension on cerebral blood flow and intracranial pressure was measured before and after the production of a standard cryogenic brain lesion in 10 anaesthetized, ventilated baboons. Before injury the animals were divided into a group with intact autoregulation, having more than 20% increase in cerebrovascular resistance during arterial hypertension, and a group with impaired autoregulation, in which the change in cerebrovascular resistance was much less. The cryogenic injury produced a rapid rise in intracranial pressure and a reduction of cerebral blood flow in the affected hemisphere. Despite this, there was an increase in cerebrovascular resistance during arterial hypertension in all animals after brain injury, accompanied by a further significant rise in intracranial pressure. It is suggested that this response is unlikely to represent normal physiological autoregulation and caution should be exercised in interpreting it as such in the course of studies of cerebral blood flow in patients with acute brain damage.