The effect of gas emboli on rabbit cerebral blood flow

Many bubbles that enter the brain circulation pass through the arterioles and capillary beds and do not obstruct blood flow. Nevertheless, such bubbles could still disrupt brain function. An open-brain model in five anesthetized rabbits used the minimum dose of air (25 microliters) necessary to cause embolism of the exposed vessels, and these bubbles passed through the vessels without any trapping. Despite their rapid transit, the bubbles provoked a marked dilatation of the affected pial arterioles (mean increase after 15 minutes of 27%) that persisted for 90 minutes after the bubbles had disappeared. The changes in vessel diameter were associated with a delayed, but significant and progressive, reduction in both cerebral blood flow measured by hydrogen clearance and neural function measured by cortical somatosensory evoked response. The decrease in blood flow correlated well with the depression of neural function (r = 0.67). Because both cerebral blood flow and neural function temporarily returned to normal after air embolism, the subsequent changes seen in this model cannot be explained simply by the mechanical obstruction of blood flow by bubbles.