With the elucidation of the "azygos flow factor" by Andreason and Watson,1 it was established that a markedly reduced venous return and cardiac output were compatible with prolonged survival in dogs. Lillehei2 has demonstrated that with caval occlusion produced at normal body temperature azygos vein flow into the right atrium is compatible with survival for periods of 30 to 60 minutes. In dogs this flow amounted to 8 to 14 ml. per kilogram of body weight per minute and was less than 10% of the basal cardiac output. The clinical application of this principle resulted in "cross circulation procedures." with blood flow between donor and patient regulated in the range of 20 to 25 ml. per kilogram per minute. This technique permitted open right cardiotomy and the surgical repair of congenital defects of the interatrial and interventricular septa.
Recently, in many laboratories, pump oxygenators have been developed to