Normal PO 2 Gradients and VO 2 in the Rat Mesentery

Rationale. The revision of Krogh's concept of oxygen transport by Tsai et al. (1998) was based on their discovery of a steep profile of PO 2 (PPO 2 ) and very high VO 2 in the vessel wall and tissue using the phosphorescence quenching method (PQM). Objective. Accurate measurements of the PPO 2 and VO 2 were made with a scanning PQM technique designed to prevent accumulated O 2 consumption by the method in the tissue. Methods. PPO 2 's (N=84) were measured in the mesentery of 7 anesthetized rats with the scanning PQM. The excitation spot (size 5×5 μm, 410 nm laser, 100 pulses at 11Hz, duration 2 μs and energy 28 pJ/μm 2 ) scanned the tissue (parallel to a vessel) with amplitude 57 μm and period 1.4 s. The tissue was loaded with the phosphorescence probe and slightly pressurized under an O 2 barrier film. Results. Tissue PO 2 above and beside arterioles (62 mmHg) was close to known intravascular values. The PO 2 at distances of 5, 15, 30, 60, 120 and 180 μm from the blood/wall interface were 62, 60, 58, 55, 45 and 28 mmHg. No difference in PPO 2 was found between small and large arterioles (13 and 27 μm). The calculated VO 2 in the tissue was 65 nl O 2 /(cm 3 · s), 3.7 times lower than reported by Tsai et al. Conclusions. No evidence was found for a low periarteriolar PO 2 or a large VO 2 in the mesentery. It appears that the high VO 2 in the tissue and arteriolar wall (240 and 65,000 nl O 2 /(cm 3 · s)), reported by Tsai et al., was the result of an experimental artifact. Supported by grants NIH‐HL18292 and AHA‐0655449U .