Cerebral blood flow regulation during experimental brain compression

✓ The effect of brain compression on cerebral blood flow was measured in 13 anesthetized, ventilated dogs by inflation of extradural balloons. The effects of the raised intracranial pressure, so produced, were correlated with the presence or absence of autoregulation of cerebral blood flow to induced changes of arterial pressure, which was tested immediately prior to each episode of inflation of the balloon. Cerebral blood flow was measured by a venous outflow method and monitored continuously, together with arterial and supratentorial intracranial pressure; arterial pCO2 and body temperature were held constant. Three stages were identified. When autoregulation to a change of arterial pressure was intact, initial inflation of the balloon did not reduce cerebral blood flow until the difference between arterial and intracranial pressure (which was taken to represent cerebral perfusion pressure) was less than 40 mm Hg. When autoregulation was impaired, which occurred after the first inflation of the balloon or was due to preceding arterial hypotension, raised intracranial pressure caused an immediate reduction of cerebral blood flow. At this stage of impaired autoregulation there was a tendency for hyperemia to develop on deflation of the balloon. Finally, after repeated inflation and deflation of the balloon, when brain swelling supervened, cerebral blood flow decreased steadily and failed to increase despite induced increases of arterial pressure and cerebral perfusion pressure.