Correlation of hemodynamics in macrocirculation and microcirculation.

The current state of our understanding on the correlation between hemodynamics in the micro- and macrocirculation is assessed. The use of microcirculatory approach has allowed the identification of the sites of microvascular responses to neuro-humoral influences which are known to affect the overall resistance determined by macrocirculatory experimentation. Direct determinations of hematocrit and apparent viscosity in microvessels have helped to interpret macrocirculatory findings on the distribution of red cells and plasma and on the pressure-flow relationships in normal and pathological conditions. Hemodynamic measurements made on microvessels in the ventricular epicardium have provided the microcirculatory bases of the variations in coronary blood flow during the cardiac cycle and the changes in coronary hemodynamics in response to vasodilators. Microcirculatory studies on the surface glomeruli of Munich-Wistar rats have allowed the identification of the sites of microvascular actions of vasoactive agents and the determination of their effects on glomerular filtration coefficient. Several attempts have been made to synthesize the overall hemo-dynamics at the organ level from microcirculatory data, with some degree of success. In order to attain the goal of correlating macrocirculatory and microcirculatory hemo-dynamics, we need to perform parallel investigations at these levels on the same organs or tissues in the same animal species, together with morphological characterization of the microcirculatory architecture and theoretical modeling in which accounts are taken of the heterogeneity of structural and functional parameters.