Impaired exercise capacity in individuals with non-obstructive small airway dysfunction

Abstract

Background: Whether individuals with non-obstructive spirometry-defined small airway dysfunction (SAD) have impaired exercise capacity is unclear, particularly in never-smokers. This study clarifies the degree of impaired exercise capacity and its potential cause in individuals with non-obstructive SAD. Methods: This community-based, multiyear cross-sectional study analyzed data collected in Guangdong, China from 2012–2019 by the National Science and Technology Support Plan Program. Measurements of exercise capacity [peak work rate and peak oxygen uptake (O2peak)] in participants with non-obstructive spirometry-defined SAD (n=157) were compared with those in controls (n=85) and Global Initiative for Chronic Obstructive Lung Disease (GOLD) I patients (n=239). Subgroup analyses were performed by smoking status. Results: The risk of impaired exercise capacity was significantly higher in participants with non-obstructive SAD [ O2peak <84%predicted, adjusted odds ratio (aOR) =2.53; 95% confidence interval (CI): 1.42–4.52] than in controls but was not significantly different from that in GOLD I patients. Results were consistent within subgroups of smoking status (ever-smokers: non-obstructive SAD vs. controls, aOR =2.44; 95% CI: 1.08–5.51; never-smokers: non-obstructive SAD vs. controls, aOR =2.38, 95% CI: 1.02–5.58). Participants with non-obstructive SAD had a significantly lower peak work rate (β=−10.5; 95% CI: −16.3 to −4.7) and O2peak (%predicted, β=−4.0; 95% CI: −7.7 to −0.2) and tended to have higher ventilatory equivalents for carbon dioxide at the ventilatory threshold (E/ CO2AT, β=1.1; 95% CI: −0.1 to 2.3) when compared with controls. Both peak work rate and O2peak were negatively correlated with E/ CO2AT. Conclusions: Although not meeting the current criteria for chronic obstructive pulmonary disease, individuals with non-obstructive SAD have impaired exercise capacity that may be associated with ventilatory inefficiency regardless of smoking status.