Following the discovery that a minimal amount of blood flow was necessary to maintain circulation, C. Walton Lillehei and his research assistants Morley Cohen and Herbert Warden began to experiment with the lung factor in circulation - oxygenation of blood.
Cohen, whose wife was pregnant at the time, thought about the physiological relationship between a mother and fetus, in which the mother’s lungs oxygenate the blood that is pumped to the fetus through the placenta. The researchers wondered whether an artificial placenta could create the same relationship for use in open heart surgery. This idea lead Cohen and Warden to test whether a donor animal could take over the circulation of a recipient in order to supply oxygenated blood to the recipient’s organs while the heart was isolated for operation.
Using a laboratory pump, catheters, and plastic tubing, they connected an artery in the neck of a recipient dog to an artery in the thigh of a donor. Another tube was connected between major veins in both animals. Deoxygenated blood from the recipient was pumped through the tubing to the donor, where it was carried to the donor’s lungs to be oxygenated. Oxygen rich blood was then returned to the recipient’s body through the vein connection. The method maintained circulation in the recipient while by-passing the heart, which was clamped off at the major vessels.