Association between impaired diffusion capacity and small airway dysfunction: a cross-sectional study

Abstract

BackgroundSmall airway dysfunction (SAD) and impaired diffusion capacity of the lungs for carbon monoxide (DLCO) are positively associated with a worse prognosis. Individuals with both dysfunctions have been identified in clinical, and it is unknown whether they had worse health status or need management. We conducted this study to explore the association between SAD and impaired DLCO, and the difference between the groups with two dysfunctions, with either one dysfunction, and with no dysfunction.MethodsThis study involved subjects partly from those who had returned for the third-year follow-up (up to December 2022) of the ECOPD Study and those who newly participated. We assessed the diffusion capacity, questionnaire, exacerbations, spirometry, impulse oscillometry (IOS), and computed tomography (CT). Impaired DLCOwas defined as DLCO%predicted <80%. Spirometry-defined SAD was defined using MMEF %predicted, FEF50%predicted, and FEF75%predicted; at least two of the three being <65% using post-bronchodilator spirometry. IOS-defined SAD was defined as R5-R20 >0.07 kPa·L−1·s−1. CT-defined SAD was defined by LAA−856% comprising ≥15% of the total lung volume. Covariate analyses and logistic regression were performed to assess the association between impaired DLCOand SAD.ResultsThis study involved 581 subjects. The occurrence of both spirometry- and CT-defined SAD was significantly higher in subjects with impaired than normal DLCOSubjects with two dysfunctions were associated with worse preceding-year exacerbations than controls.ConclusionsImpaired diffusion capacity is positively associated with SAD. Subjects with impaired diffusion capacity and SAD may have a worse health status and need additional management.