The effect of cardiopulmonary bypass on cerebral blood flow

The experiments dealth with the effect of total cardiopulmonary bypass on global and regional cerebral blood flow. Global cerebral blood flow was determined with radioactive microspheres, regional cerebral flow by direct observation through transillumination and high-speed cinematography. The latter permitted observations of changes in caliber of cerebral arterioles and of red cell velocity. Arterial blood gas tension and pH were continuously monitored. Measurements were carried out prior to and immediately following cardiopulmonary bypass. Studies on global cerebral flows showed that during cardiopulmonary bypass cerebral blood flow rose and cerebral vascular resistance declined while blood pressure did not change significantly. During bypass, cerebral blood flow and blood pressure in animals treated as a group became interdependent and showed direct proportionally. Direct observations of the cortical microvasculature by means of high-speed cinematography revealed dilatation of cerebral cortical arterioles. Even though blood pressure remained unchanged, the diameter of cortical arterioles increased. Volume flow calculated from red cells velocity and arteriolar diameter showed a tendency of arteriolar flow to increase. The condition is reminiscent of the 'luxury perfusion syndrome' (overabundant cerebral flow relative to metabolic needs of cerebral tissue).