Although lung diffusing capacity for carbon monoxide (DLCO) is a widely used test of diffusive O2 transfer, few studies have directly related DLCO to O2-diffusing capacity (DLO2); none has used the components of DLCO, i.e., conductance of alveolar membrane and capillary blood, to predict DLO2 from rest to exercise. To understand the relationship between DLCO and DLO2 at matched levels of cardiac output, we analyzed cumulative data from rest to heavy exercise in 43 adult dogs, with normal lungs or reduced lung capacity following lung resection, that were studied by two techniques. 1) A rebreathing (RB) technique was used to measure DLCO and pulmonary blood flow at two O2 tensions, independent of O2 exchange. DLCO was partitioned into CO-diffusing capacity of alveolar membrane and pulmonary capillary blood volume using the Roughton-Forster equation and converted into an equivalent DLO2, [DLO2(RB)]. 2) A multiple inertgas elimination technique (MIGET) was used to measure ventilationperfusion distributions, O2 and CO2 exchange under hypoxia, to derive DLO2 [DLO2(MIGET)] by the Lilienthal-Riley technique and Bohr integration. For direct comparisons, DLO2(RB) was interpolated to the cardiac output measured by the Fick principle corresponding to DLO2(MIGET). The DLO2-to-DLCO ratio averaged 1.61. Correlation between DLO2(RB) and DLO2(MIGET) was similar in normal and post-resection groups. Overall, DLO2(MIGET) = 0.975 DLO2(RB); mean difference between the two techniques was under 5% for both animal groups. We conclude that, despite various uncertainties inherent in these two disparate methods, the Roughton-Forster equation adequately predicts diffusive O2 transfer from rest to heavy exercise in canines with normal, as well as reduced, lung capacities.
- Lung resection
- Multiple inert-gas elimination technique
- Oxygen-diffusing capacity
- Rebreathing technique
- Roughton-Forster relationship
ASJC Scopus subject areas
- Physiology (medical)