Measurement of oxygen in the microcirculation using phosphorescence quenching microscopy

According to the classical concept of Krogh, O(2) is delivered to the tissues solely by capillaries and intra-capillary resistance to O(2) diffusion is negligible. Over the past three decades longitudinal PO(2) and SO(2) gradients in arterioles have been observed with a transmural PO(2) gradient in small arterioles of only 1-2 mmHg. Application of phosphorescence quenching microscopy to measurements of PO(2) in arterioles of the rat mesentery by Tsai et al. (1998) found a large transmural PO(2) in these arterioles. That led to the provocative conclusion that the arteriolar wall is the major sink for O(2) in the microcirculation. Our studies indicate that many of these results can be explained by photo-activated O(2) 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.