Oxygen transport is believed to primarily occur via capillaries and depends on the oxygen tension gradient between the vessels and tissues. As blood flows along branching arterioles, the O2 saturation drops, indicating either consumption or diffusion. The blood flow rate, the O2 concentration gradient, and Krogh’s O2 diffusion constant (K) of the vessel wall are parameters affecting O2 delivery. We devised a method for evaluating K of arteriolar wall in vivo using phosphorescence quenching microscopy to measure the partial pressure of oxygen in two areas almost simultaneously. The K value of arteriolar wall (inner diameter, 63.5 ± 11.9 μm; wall thickness, 18.0 ± 1.2 μm) was found to be 6.0 ± 1.2 × 10－11 (cm2/s)(ml O2?cm－3 tissue?mmHg－1). The arteriolar wall O2 consumption rate (M) was 1.5 ± 0.1 (ml O2?100 cm－3 tissue?min－1), as calculated using Krogh’s diffusion equation. These results suggest that the arteriolar wall consumes a considerable proportion of the O2 that diffuses through it.
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