BRIEF REVIEWS Flow-Induced Trauma to Blood Cells

THE TECHNOLOGY of implantable vascular prostheses and extracorporeal circulation is now commonplace in modern medicine. The essential function of this technology is the passage and/or processing of blood in some manner, and this inevitably requires intimate and prolonged contact between the blood and various manmade devices, e.g., pumps, valves, tubing, membranes, etc. Some systems, such as the extracorporeal heart-lung bypass, may be used acutely for periods of only a few hours but others are implanted for indefinite terms. In either case the associated blood trauma must be kept within tolerable limits. In surgical practice blood trauma is often a limiting factor in the duration of an acute procedure. It can also cause significantly abnormal physiological states during chronic exposures such as hemodialysis. To cope with these problems will require a thorough understanding of how blood is traumatized during circulation through artificial organs. It is only through such understanding that rational criteria for the design of these systems can evolve. Reports of blood degradation associated with artificial organs have been appearing in the literature for at least 20 years. The majority of the very early papers dealt with the hemolytic anemia generally found following the installation of valvular protheses. It was not until the mid-1960's that the attack on the problem began to take a more scientific turn by focusing on the mechanisms responsible for blood trauma rather than the mere reporting of the amount of trauma produced by particular devices or procedures. Attracted by the challenging fluid-mechanical and transport aspects of the problem, many engineers with experience in these disciplines joined medical colleagues in formulating theoretical and experimental studies of flow-induced blood trauma. As a result, most of the research groups which have contributed consistently in this area tend to be highly interdisciplinary. Indeed, like the entire field of artificial organs, the blood degradation problem has provided a fruitful meeting ground for the life scientist and the engineer.