Background: DLCO is the product of the CO transfer coefficient (KCO) by the "accessible" alveolar volume (VA). In theory, the same DLCO may result from various combinations of KCO and VA values, each of which reflect different injury sites and mechanisms. We sought to determine in this study the potential variability of both VA and KCO for fixed values of DLCO in diffuse parenchymal lung diseases (DPLD).
Methods: To this end, we designed a retrospective, cross-sectional study of three distinct types of DPLD and analysed pulmonary function test (PFT) datasets.
Results: We show here that for the same value of DLCO (50% predicted), KCO varied from 60 to 95% predicted and VA from 55 to 85% predicted in various types of DPLD idiopathic pulmonary fibrosis, sarcoidosis and connective tissue disease-associated DPLD, indicating distinct pathogenic mechanisms in these diseases. In addition, a comparison of VA with total lung capacity may help to evidence the distal airway obstruction sometimes associated with certain DPLD particularly sarcoidosis.
Conclusion: Clinicians should take into account not only DLCO but also VA and KCO values when managing patients with DPLD.