Diffusing Capacity for Nitric Oxide and Carbon Monoxide in Patients With Diffuse Parenchymal Lung Disease and Pulmonary Arterial Hypertension: Conclusion
There have been several studies dealing with the subdivision of the Dlco in interstitial lung diseases. In 1976, Saumon et al found that in patients with sarcoidosis with radiologic stage I and II disease, the decrease in Dlco was mainly due to decreased Dmco, but that in stage III sarcoidosis the decrease was associated with a decrease in Vcap. The Vcap values in subjects with IPF or due to systemic sclerosis were lower than in the sarcoidosis stage III group. Phansalkar et al measured rebreathing Dlno and Dmco values in 25 subjects with stage II-III sarcoidosis compared to 18 healthy nonsmoker subjects. They found a resting Dlno/Dlco ratio of 4.36 in healthy subjects and 3.48 in subjects with sarcoidosis. At 80% of peak workload, the ratios were 3.70 in healthy subjects and 2.97 in subjects with sarcoidosis. Indeed, at rest and during exercise the Dlno/Dlco ratios were lower in subjects with sarcoidosis than in healthy subjects, as expected. Reading here
The Dlno strongly correlated with the Dmco, indicating that the Dlno closely resembles the true diffusing capacity of the alveolar capillary membrane. The fact that Phansalkar et al found lower ratios in subjects with sarcoidosis than we did is troubling. Although Phansalkar et al included subjects with stage II-III sarcoidosis compared to our inclusion of subjects with stage I-IV disease, it is unlikely that this explains the difference. The rebreathing technique used by Phansalkar et al is performed at the functional residual capacity level, in contrast to our actual measurement at the total lung capacity level as occurred when using the single-breath method. This could explain in part the difference between the findings of Phansalkar et al and our own. In 2004, Lamberto et al measured the Dmco and the Vcap in patients with stage I-IV sarcoidosis and found that the reduced Dlco was caused mainly by lowered Dmco in all groups. Furthermore, Dmco as well as Dlco are highly predictive of gas exchange abnormalities during exercise.