New phosphorescence quenching oxygen measurements technique yields unusual tissue and plasma Po2 distributions

Abstract

To the Editor: Wilson et al. (9) report using a novel group of chromophores for measuring oxygen pressure in the interstitial space and blood plasma, proposing that the histogram of PO2 volume distribution measured in the thigh muscle of mice can be used to 1) describe the partition of tissue and intravascular PO2 and 2) characterize the difference between intra- and extravascular PO2 or the vessel wall gradient. Both contentions would appear to be at odds with the results and data presented. Their histograms (Fig. 2) show intra- and extravascular PO2 volume fractions of 10 and 20%, respectively, with PO2 values of 100 –140 Torr. The maximum PO2 in arterial blood leaving the lungs is 100 mmHg, and the existence of a longitudinal gradient downstream is a well established feature of PO2 in the vasculature (8). Even in small animals, it is not clear how the PO2 of blood in the vasculature or the tissue of the limbs can exceed PO2 of blood in the lungs. A measurement technique that records such high PO2 values in the interstitial and the intravascular space raises questions about how the measurements relate to the distribution of PO2 in the tissue reported by previous investigators. The review of Tsai et al. (8) on oxygen gradients in the microcirculation shows that the highest PO2 value recorded in 12 studies of arterioles up to 100 m using either the micro