The objective of this project was to determine the profile of oxygen partial pressure (PO2) inside small vessels in a hamster model. Microcirculation of skeletal skin muscle and subcutaneous connective tissue was visualized in a dorsal skin-fold. The system allows noninvasive in vivo measurement of intravascular PO2 at the microscopic level. PO2 determination is based on the O2-dependent quenching of phosphorescence of palladium-porphyrins hound to albumin. This compound was injected intravenously in the dosage of 0.1 ml probe/ 100 g animal. The phosphorescence emission was excited by epiillumination with a strobe Xenon arc (415nm) and measured by a photomultiplier in a well-defined area as small as 5 × 1.5 μm. A selected portion of the phosphorescence decay was fitted by a single exponential, and the Stern-Volmer equation was used to calculate P02. Simultaneous transillumination of the tissue also allows measurement of vessel diameter and red blood cell velocity in the same vessel. This study shows that there is a small PO2 loss around the center for the microvessel in opposition is a substantial PO2 loss from the blood as it passes through the arteriolar network.Figure 1: Caption Not Available.