Timothy Secomb, PhD, studies the microcirculation, a network of extremely small blood vessels that supply oxygen and nutrients to all parts of our tissues. The focus of work in his research grouis the use of mathematical and computational approaches to study blood flow and mass transport in the microcirculation. Working in collaboration with experimentalists, the aim is to understand quantitatively the processes involved. Dr. Secomb examines the relationshibetween red blood cell mechanics and flow resistance in microvessels. Theoretical predictions agree well with observations in glass tubes, but resistance is higher living tissue. The major cause is the presence of a relatively thick macromolecular lining endothelial surface layer) on the walls of microvessels. He also simulates oxygen exchange between networks of microvessels and surrounding tissues in skeletal muscle and tumors. In skeletal muscle, oxygen can be exchanged diffusively between arterioles and capillaries, and Dr. Secomb’s lab is studying the determinants of maximal oxygen consumption. In tumors, the relationshibetween network structure and occurrence of local hypoxic radiation-resistant) regions is a source of curiosity. They are analyzing the delivery of chemotherapeutic drugs in tumor tissues, and developing improved models to describe the responses of tumor cells to chemotherapy and radiation. Models for the structural responses of microvessels to functional demands are being developed. Maintenance of a stable, functionally adequate distribution of vessel diameters can be achieved if each vessel responds to changes in wall shear stress, intravascular pressure and local metabolic conditions, and if mechanisms exist for information transfer upstream and downstream along flow pathways. Models for the active regulation of blood flow by changes in vascular tone are also being developed, taking into account vascular responses to wall shear stress, pressure and local metabolic state, and including effects of conducted responses along vessel walls. Another project in the grouis the development of computer simulations for the dynamics of the left ventricle that can be run in real time and provide a tool for analysis of data derived from ultrasound echocardiography images.