Simultaneous measurement of blood flow distribution and oxygen tension by photo-excitation in organ microcirculation

The microcirculatory system plays a very important role in delivering oxygen and materials to tissues and organs. In this study, the authors set up a new system with two light sources to measure blood flow velocity, vessel diameter, and pO₂ simultaneously in organ microcirculation. Pd-meso-tetra(4-carboxyphenyl)-porphyrin was employed as an oxygen-sensitive probe, and was excited with the second harmonic of a Nd:YAG pulse laser (wavelength: 532 nm) at 1 Hz. The phosphorescence lifetime was obtained from the emission decay curve and pO₂ was calculated from the Stern-Volmer equation. At the same time, blood flow in organ microvessels was visualized by perfusing red blood cells labeled with fluorescent isothiocyanate. Blood flow velocity and vessel diameter were quantified by processing images with a personal computer. Through measurements on rats in vivo, the changes in blood flow velocity and pO₂ in organ microvessels were quantified during asphyxia and hemorrhagic shock. The results demonstrate that the system can measure blood now and oxygen delivery in the microcirculatory system. In the future, the authors will use this system to analyze pathologic physiology, such as blood flow change in diabetes mellitus