Time-Dependant Oxygen Partial Pressure in Capillaries and Tissue in the Hamster Window Chamber Model

Abstract

The possibility of a plasma oxygen diffusion barrier implies a significant resistance to oxygen diffusion and the existence of capillary erythrocyte-associated transients of oxygen. This effect was analyzed by measuring intracapillary blood and tissue pO₂ in the hamster chamber window model using a noninvasive intravital microscopy palladium porphyrin phosphorescence decay technique for two set light excitations (high and low). Using high light excitation, intracapillary blood pO₂ was 13.7 ± 6.1 mm Hg, and increased to 18.0 ± 4.5 mm Hg for low light excitation. For high light excitation, intracapillary blood pO₂ peaks were in the range of 25–30 mm Hg, and the lowest values were in the range of 5–10 mm Hg. Reducing the excitation provided a more uniform pO₂ ranging 15–25 mm Hg. With temporal reduction in blood capillary pO₂, levels were correlated to the increase in phosphorescent amplitude that corresponded to plasma gaps. Tissue pO₂ measured at low light excitation in the proximity of capillaries was 23.1 ± 1.8 mm Hg. In conclusion, low intracapillary blood pO₂ measurements at full hematocrit are an artifact, only observed when oxygen consumption by the measurement technique was excessive and/or absorption of the excitation light was increased by the absence of RBCs. These findings suggest that resistance to oxygen diffusion in plasma is a minor factor in tissue oxygenation by capillaries in the hamster model.