Effect of constricting carotid arteries on cerebral blood flow and on cerebrospinal fluid pH, lactate and pyruvate in dogs.

Cerebral perfusion pressure was reduced by graded constricting of both carotid arteries in the anesthetized dogs, of which vertebral arteries were ligated bilaterally. Cerebral blood flow and cerebral metabolic rate of oxygen remained unchanged until cerebral perfusion pressure was lowered to about 50 mm.Hg, indicating that cerebral autoregulation was preserved normally in these animals. Despite a slight decrease in arterial lactate levels, there was a progressive increase in lactate with a concomitant decrease in pH of cisternal cerebrospinal fluid (CSF) even during the autoregulatory range of cerebral perfusion pressure, suggesting that increase in CSF lactate resulted primarily from increase in brain tissue lactate. Increased CSF lactate/pyruvate ratio and decreased cerebral cortical blood flow suggest that brain tissue tends to be hypoxic, although cerebral blood flow remained unchanged. It could be concluded that the mechanism of regulating cerebral blood flow constant in response to lowered perfusion pressure is a function of CSF lactic acidosis resulting from brain tissue hypoxia.