BLOOD FLOW IN VASCULAR TREES

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It has not been possible to determine the functioning of a tissue or organ from detailed observations of individual microvessels. In an effort to understand how the behavior and response of tissues are related to microcirculatory events, there has been great interest in studying microvessel networks. A major goal of this work has been to develop computer network models of the microvasculature. These models incorporate information on network topology, vessel dimensions as well as peculiarities of blood rheology in small tubes. These peculiarities include the Fahraeus effect (reduction in hematocrit in small bore tubes), Fahraeus-Lindqvist effect (lower resistance to flow in small tubes) and plasma skimming at bifurcations. Despite these efforts, there is still a lack of agreement between theoretical computations and experimental observations. The research of this proposal focuses attention on the serial nature of the branching pattern in vessel networks, which has been neglected in previous studies. A branching tree pattern will be used as a model of the recurring unit of the network. Serial bifurcations generate disturbances in the concentration profiles of the various blood components (red cell, white cells, platelets and plasma). These disturbances can be propagated downstream to the next branch depending on the magnitude of the disturbance, the distance between the junctions and the velocity of the blood. Recent experimental and theoretical work on phase separation of blood in serial bifurcations permit inclusion of these phenomena into microvessel network models. This research will be a computational study of the distribution of blood cells in a vascular tree. Besides including the effects of asymmetric concentration profiles, this study will also examine the influence of the three dimensional arrangement of the branches in a network. The goal of the project is to determine if these new concepts cause significant changes in the computational results of network simulation. Based on the results of this theoretical work, experimental verification in animals is anticipated.