Theta values for C 16 O 18 O and C 18 O 2 related to respective pulmonary diffusing capacities

• Published in: American journal of physiology. Regulatory, integrative and comparative physiology integrative and comparative physiology, 1998-05, Vol.274 (5), p.R1496-R1499
• Main Authors: Heller, Hartmut, Schuster, Klaus-Dieter
• Format: Article
• Language: English
• ISSN: 0363-6119; 1522-1490
• DOI: 10.1152/ajpregu.1998.274.5.R1496

The single-breath diffusing capacities for singly and doubly O-labeled CO ,[Formula: see text]and[Formula: see text], as well as for NO, were determined in seven anesthetized rabbits to investigate whether the theoretically predicted ratio of specific blood uptake rates of both isotopic CO species,[Formula: see text]/[Formula: see text]= 2.0, can be derived from the measured values of[Formula: see text]and[Formula: see text]. Data of Dl were obtained by inflating the lungs with gas mixtures containing 0.35% C O O or 0.8% C O or 0.05% NO in nitrogen, with breath-holding periods of 0.05-0.5 s and 2-12 s for the CO and NO tests, respectively.[Formula: see text]/[Formula: see text]was calculated by applying the double-reciprocal Roughton-Forster equation to Dl values obtained in each animal and by assuming that NO diffusing capacity represents the gas conductance of the alveolar-capillary membrane. The measured ratio was[Formula: see text]/[Formula: see text]= 1.9 ± 0.2 (mean ± SD), thus comparing reasonably with the predicted one. Therefore, our findings provide evidence that the greater value of[Formula: see text]is mainly due to the twofold higher probability (or theta value) for C O than for C O O to disappear within red blood cells via isotopic exchange reactions.