Abstract
Heart-lung machines can effectively oxygenate blood, but their prolonged use causes difficulties not directly related to the patient's heart condition or the specific procedures used to correct it. In extreme cases a patient may be seriously affected and may develop thromboses, abnormal permeability of the vascular system (particularly in the lungs), blood clots, and occasionally brain damage (1, 2). The results of several studies (3-6) suggest that denaturation of blood proteins at blood-gas interfaces in the heart-lung machine may be responsible for some of the postoperative difficulties.
We have found no specific studies of the effects of the gas/liquid interfaces in the heart-lung machine on individual blood proteins. Therefore, we undertook an investigation of the denaturation of gamma globulin, albumin, and their mixtures in the disc oxygenator. The advantage of studying individual blood proteins is that the results can be interpreted more easily than studies with whole blood. However, data obtained in this simple model system can, at best, tell only part of the story regarding the medical complications of open-heart surgery.
We chose to work with gamma globulin because of its instability at the gas/liquid interface. This instability is easily demonstrated. If a stream of air is passed through a clear solution of gamma globulin, a precipitate of the aggregated protein rapidly forms. Albumin was selected for study because it is one of the principal components of whole blood and because it is often added to solutions of labile proteins as a stabilizer.
The Complement System and Denatured Gamma Globulin. The complement system can be activated by interaction with antigen–antibody complexes or by interaction with heat denatured, aggregated gamma globulin. Activation is known to increase capillary permeability, to enhance phagocytosis, to initiate chemotactic migration of leucocytes, and to damage membranes (7, 8).
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