This proposal's objective is to obtain data that will contribute to understanding peripheral vascular function including 1) Relationships between changes in total and active vascular volumes, tissue blood flow distribution, hemodynamics and capillary transfer mechanisms; 2) Assessment of methods for determining capillary availability (filtration coefficient, permeability surface area product, visual observation); 3) Responses of the microcirculation of specific tissues to electrical stimulations of CNS structures, 4) Reactivity or tone of distributing blood vessels and the consequent effect on blood flow distribution; 5) Investigation of relationships between capillary surface area and size of interstitial space available. Simultaneous measurements in isolated areas of capillary filtration, diffusion capacity, vascular volume and resistances during various hemodynamic conditions will be done. Systematic investigation of a number of influences on the circulatory components is planned using e.g., the isolated dog forelimb, isolated gracilis muscle, visualized areas of the microcirculation, and isolated blood vessels. It should then be possible to better evaluate the changes in capillary hydrostatic pressure and capillary surface area as they affect the kind and amount of material transferred across the capillary barrier. The problem of blood shunting from the true capillaries will be considered. Vascular segment resistances, volume changes and segment diameters for interpretations of vascular smooth muscle activity will be made. The volume of blood and its distribution is important in understanding the etiology of shock, congestive failure of the circulation, diseases causing plasma protein concentration changes, or red cell concentration change.