The in vivo pH of the extravascular space of the lung

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Abstract
The partition of 5,5-dimethyloxazolidine-2,4-dione (DMO) and of 11 amines between the vascular and extravascular spaces of the lung has been determined by the multiple indicator dilution technique. Four amines (nicotine, pentylamine, quinine, and benzylamine) were found to have pH-sensitive tissue to blood concentration ratios. Of these, tritiated nicotine appears to be the nost satisfactory indicator of tissue pH and values for the pH of the pulmonary extravascular space (pHe) have been calculated from the nicotine data. At an arterial pH (pHart) between 7.38 and 7.43 pHe averaged 6.69 ±0.07. Changes in pHe usually paralleled but were consistently less than concomitant changes in pHart. Alterations in PCO2 at constant pHart regularly produced relatively small, parallel changes in extravascular hydrogen ion concentrations. Local alterations in tissue pH due to PCO2 changes are apparently buffered quite rapidly and the pHe of the lung seems more closely linked to pHart than the cellular pH of other tissues. DMO, guanidine, methylamine, morphine, and atropine were confined to the vascular volume during the first circulation and could not be used to measure tissue pH. Histamine appeared to be bound to a pH-insensitive site. The extravascular distributions of antipyrine and aniline were unresponsive to alterations in arterial pH, presumably because they are essentially uncharged at pH levels found in the lung.