Occlusion of the thoracic aorta for prolonged periods of time is often followed by ischemic damage or death. Considerable variation in the ability of animals and man to withstand this insult has been recorded in the literature. Since the amount of collateral blood flow reaching the lower part of the body during the time of aortic cross clamping is probably one of the most important factors contributing to the animal's eventual survival, it seemed worth while to study some of the circumstances that might affect this mechanism. In this report, the influence of the level and extent of aortic occlusion relative to the amount of collateral blood flow serving the tissues below the clamps was studied.
Mongrel dogs were used. Anesthesia was induced and maintained by the intravenous administration of 3 to 4 ml. of 5% thiopental sodium. An endotracheal tube was passed, and oxygen was administered by means