FLUID DYNAMIC AND HEMORHEOLOGIC CONSIDERATIONS

The previous edition of this work, published in 1985 (1), included a s ection on fluid dynamic and hemorheologic considerations in which the basic concepts of fluid flow, protein and cell transport, and blood rh eology were presented. That material will not be reiterated in depth i n this chapter but rather referred to as appropriate. Instead, die pre sent chapter will attempt to consider the current status of research i n this field and, to the extent possible, indicate those areas where o ur understanding is incomplete and in need of additional research effo rts. Since die publication of the previous edition, our appreciation o f the ability of fluid dynamic forces to influence blood-surface inter actions has increased considerably. Progress has been made, not necess arily with respect to a detailed understanding of the manner in which fluid forces affect the behavior of materials in contact with blood in vivo, but rather in the growing recognition that the various blood an d vascular cells exist in a dynamic environment in which flow contribu tes to an essential modulation of homeostatic events. In recognition o f the complexity of the various biological processes that can occur in the presence of a graft implant or an organ replacement, a mechanisti c rather than phenomenologic approach has slowly evolved that emphasiz es the manner by which changes in fluid flow can affect the behavior o f individual cells or proteins and their possible interaction with for eign materials. The approach here will be to consider die simplest cas e of blood flow and mass transport in a tube, as was done in the previ ous edition, and to delineate not only how basic characteristics of th e system influence blood-material interactions, but also to distinguis h where such simplifications can be misleading with respect to intrava scular events or extracorporeal circuits. A description will be made o f how the principles of blood flow and mass transport are being applie d to such complicated events as cell proliferation and thromboembolism . In addition, die ability of shear stresses generated as a consequenc e of blood flow to modulate the biological activity of various cells w ill be discussed. Finally, several devices currently used to study the role of fluid flow in thrombotic and hemostatic processes will be des cribed.