Different K(CO) and V(A) combinations exist for the same DL(CO) value in patients with diffuse parenchymal lung diseases

BACKGROUND: DL(CO) is the product of the CO transfer coefficient (K(CO)) by the “accessible” alveolar volume (V(A)). In theory, the same DL(CO) may result from various combinations of K(CO) and V(A) values, each of which reflect different injury sites and mechanisms. We sought to determine in this study the potential variability of both V(A) and K(CO) for fixed values of DL(CO) 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 DL(CO) (50 % predicted), K(CO) varied from 60 to 95 % predicted and V(A) 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 V(A) 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 DL(CO) but also V(A) and K(CO) values when managing patients with DPLD.