The specific studies of blood rheology included in the Center's efforts are: 1. Investigation of cellular deformability of blood cells, a category comprising studies of blood cell shape changes, examination of membrane rheologic features as well as extrinsic determinants of cell behavior in in vitro and in vivo capillary systems, and characterization of parameters which determine rheologically significant events in bone marrow release and splenic destruction of blood cells. 2. Theoretical studies of the microcirculation focussing on mathematical modelling of individual erythrocytes, aggregates of erythrocytes and platelet flow behavior and application of theoretical models to understanding of regulation of simple capillary flow, dynamics of capillary obstruction and role of blood cells in thrombosis in the microcirculation. 3. Studies intended to promote understanding of tissue oxygenation as a function of capillary dynamics, anemia, capillary obstructive phenomena, & Hb function. Within this framework, measurement of oxygen flow to tissue cells, evaluation of specific deleterious effects of capillary occlusion, (e.g., sickle cell obstructive phenomena), both anemia and polycythemia on tissue oxygenation. 4. Efforts to characterize fundamental structural proteins of erythrocyte membranes, identify functionally important molecular interactions and correlate these properties with observed rheologically important viscoelastic and tensile strength of normal and pathologic cell membranes. There have been no significant changes in the goals or directions of this program. BIBLIOGRAPHIC REFERENCES: Henquell, L., P.L. Celle and C.P. Honig. Capillary Diameter in Rat Heart in situ; Regulation to Erythrocyte Deformability, 02 Transport and Transmural 02 Gradients. Microvasc. Res. 12:259, 1976. Kirkpatrick, F.H., G.M. Woods, R.I. Weed and P.L. La Celle. Fractionation of Spectrin by Differential Precipitation with Calcium. Arch. Biochem. Biophys. 175:367, 1976.