Determination of Tissue 02 Tensions by Hollow Visceral Tonometers : Effect of Breathing Enriched 02 Mixtures * EDWARD

The concentrations of 02 and CO2 in tissues (i.e., the extracellular tissue spaces) can be an index to the relationship between the blood flow and metabolism of an organ. Since the optimal performance of an organ is expected to occur between definable limits of the tissue 02 and CO2 tensions (1, 2), correct values for these gas tensions delineate the most suitable relationship between flow and metabolism during various physiological circumstances. Numerous methods have been devised to measure respiratory gases in tissues, but each is hampered by artifacts that are likely to alter the gas tensions: polarographic needle electrodes implanted in tissues often rupture capillaries or compress blood vessels (3); subcutaneous gas depots are usually associated with extensive pathological changes in contiguous tissues (4, 5); and even a method equating the gas tensions of lymph to those of interstitial fluid results in variable values (6, 7). With these difficulties, it has, for practical purposes, been assumed that the respiratory gas tensions of the draining venous blood are reasonable estimates of the tissue gas tensions; however, comparisons of values for tissue and venous blood gas tensions in a single organ in order to validate this assumption have not been performed. The present study investigates the hollow viscus as a convenient in vivo tonometer in which to equilibrate liquids until they assume the gas tensions of the surrounding tissues. We found that such organs as the urinary bladder act as very rapid and convenient tissue tonomneters and that it is