Abstract
BackgroundDLCO 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).MethodsTo this end, we designed a retrospective, cross-sectional study of three distinct types of DPLD and analysed pulmonary function test (PFT) datasets.ResultsWe 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.ConclusionClinicians should take into account not only DLCO but also VA and KCO values when managing patients with DPLD.
Highlights
carbon monoxide diffusing capacity (DLCO) is the product of the CO transfer coefficient (KCO) by the “accessible” alveolar volume (VA)
Raw pulmonary function test (PFT) data were provided and % predicted values were subsequently calculated by a single investigator (CD2) for the whole population according to Stanojevic for spirometry [9] and other international recommendations for DLCO and static lung volumes respectively [10, 11]
On an individual patient basis, a similar DLCO could be obtained from various combinations of rate for carbon monoxide uptake (KCO) and VA (Fig. 1)
Summary
DLCO is the product of the CO transfer coefficient (KCO) by the “accessible” alveolar volume (VA). 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). A secondary objective was to determine whether a low VA value in this context might reflect a distal airway obstruction in addition to a potential restrictive defect To this end, we designed a retrospective, cross-sectional study of three distinct types of DPLD: idiopathic pulmonary fibrosis (IPF, the prototype for fibrotic pulmonary diseases predominantly affecting the lower lobes), stage IV sarcoidosis (predominantly affecting the upper lobes) and connective tissue disease-associated interstitial lung
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