Measurement of Oxygen in the Microcirculation Using Phosphorescence Quenching Microscopy

Abstract

According to the classical concept of Krogh, O₂ is delivered to the tissues solely by capillaries and intra-capillary resistance to O₂ diffusion is negligible. Over the past three decades longitudinal PO₂ and SO₂ gradients in arterioles have been observed with a transmural PO₂ gradient in small arterioles of only 1–2 mmHg. Application of phosphorescence quenching microscopy to measurements of PO₂ in arterioles of the rat mesentery by Tsai et al. (1998) found a large transmural PO₂ in these arterioles. That led to the provocative conclusion that the arteriolar wall is the major sink for O₂ in the microcirculation. Our studies indicate that many of these results can be explained by photo-activated O₂ consumption following phosphor excitation, combined with a large excitation area and high frequency of flash excitation. We have developed the basic principles for phosphorescence quenching microscopy including the need to use a small excitation area, a low excitation frequency and a scanning excitation for stationary samples.