Heart pump and oxygenator.

1124 T ms PAPER is a general review of the development of the artificial heart-lung to facilitate open-heart surgery. At the close of World War II many centers began investigating the possibility of total cardiac bypass. Oven the past decade, pump oxygenerators of various types have become popular and recent clinical successes throughout the world have given further impetus to the study of problems posed by the artificial heart-lung apparatus. The subject divides itself into three separate parts, the first two being concerned with the maintenance of life in an expenimental animal during a total cardiac bypass. One must take all the blood from the animal and return it to the animal by means of a pump. Secondly, one must oxygenate the blood before returning it. The third pant of the problem confronting the surgeon is the selection of cases and conrection of defects in human subjects. The pumping mechanism must duplicate as nearly as possible the action of the chambers of the heart. Pumping action must be smooth so as to prevent hemolysis and to avoid turbulence with thrombosis. It is not difficult to construct a pump with which hemolysis can be kept to relatively negligible amounts. Most of the pumps in use throughout the world give an hemolysis of less than 50 mg of hemoglobin pen 100 ml of blood, which is perfectly safe. Tunbuhence with thrombosis can be overcome by removing valves inside the stream and placing valves outside of, rather than within the stream of blood. Furthermore, hepaninization of the blood lessens the tendency to thrombosis. It was the experience of all the early investigators, including ourselves, that postoperative bleeding was a serious complication. It was not until the neutrahizing effect of protamine on heparin was appreciated that many dogs survived a simple bypass for any length of time without bleeding to death. This postoperative bleeding, due both to hepaninization and perhaps to the reduction of platelets from prolonged extracorporeal pumping, was overcome by administration of protamine and successes were achieved. The problem of delivering the blood to the experimental animal is relatively simple. It can be delivered into a subclavian artery where it passes centrally, closes the aontic valves and is redistributed to the body. This is the common practice with most surgeons in both experimental and clinical apphication at the present time. The actual removal of the blood from the dog constituted a major problem in the early phases of study. It was not until catheters were inserted through the right aunicubar appendage into the superior and inferior vena cavae that the removal of the blood was adequate. Even this presents occasional hazards and some controversy exists as to whether one should remove this blood by a vacuum pump or by gravity. Certainly, if one increases the pressure slightly the cannulae are apt to become blocked, and it may be that suction through the vena cavae causes some deleterious effect on both liven and brain. Gravity methods of removal are not always certain although in use in some centers. The oxygenation of the blood proved at first to be a most difficult stumbling block. It was felt that large quantities of blood would have to be oxygenated to approach the normal flow, that is, somewhere in the neighborhood of 4 to 6 1/mm, and a tremendous surface must be created to oxygenate such a large quantity of blood. It