Prevalence and Risk Factors of Spirometry-Defined Small Airway Dysfunction in the High-Risk Population for COPD in Yunnan Province, China: A Population Based Cross-Sectional Study

Small airway dysfunction (SAD) is a key early marker of chronic obstructive pulmonary disease (COPD) development. While many studies have examined the link between SAD and early COPD, the epidemiology of SAD in high-risk COPD populations remains understudied. This cross-sectional study utilized a multi-stage randomized cluster sampling method and recruited 11,095 adult residents aged ≥20 years from different elevations in Yunnan Province, China. High-risk individuals were identified using screening questionnaires and subsequently underwent pulmonary function tests. COPD was diagnosed based on post-bronchodilator test results. Spirometry-defined SAD was defined as the presence of at least two out of three indicators (MMEF, FEF50%, FEF75%) being below 65% of the predicted values. Multivariate logistic regression models were employed to examine the influencing factors of spirometry-defined SAD. Of 2191 high-risk COPD subjects aged ≥40 years, 1186 (54.1%) had spirometry-defined SAD. Notably, 49.9% of spirometry-defined SAD cases had coexisting COPD, and 97.4% of COPD patients exhibited spirometry-defined SAD. Multivariable analysis identified the following risk factors for spirometry-defined SAD: advanced age, low BMI, limited education, childhood respiratory disease history, tobacco exposure, and residence at lower altitudes. The study found a high prevalence of spirometry-defined SAD in individuals at high risk for COPD, with nearly all COPD patients exhibiting spirometry-defined SAD in this cohort. Risk factors for spirometry-defined SAD included older age, low BMI, low education level, childhood respiratory disease history, tobacco exposure, and lower altitude residence.