Contribution of small airway disease to dynamic hyperinflation in patients with chronic obstructive pulmonary disease

Lung hyperinflation is a treatable trait in chronic obstructive pulmonary disease (COPD) that can often only be detected on exertion. Air trapping in these patients results from the premature closure of the small airways. This study aimed to assess the association between small airway disease (SAD) and dynamic hyperinflation (DH) induced by the Glittre-daily life activities test (TGlittre) in COPD patients. This is a cross-sectional study in which 54 patients with COPD underwent TGlittre coupled with dynamic ventilation measurements. They also underwent the COPD Assessment Test (CAT) questionnaire, the St. George's Respiratory Questionnaire (SGRQ), spirometry, and respiratory oscillometry (RO). In the TGlittre, 30 (55.6%) participants presented DH (DH group), while 24 (44.4%) did not (NDH group). When comparing these two groups, we observed no statistical difference concerning the CAT score, SGRQ score, and spirometric parameters. Respectively, 27 (90%) and 9 (37.5%) participants in the DH and NDH groups presented changes in the RO, with the DH group showing higher values in reactance area [Ax, 24.7 (17-46) vs. 6.1 (4-9) cm H2O/L/s, p<0.0001] and resonance frequency [Fres, (8 (4.3-17.9) vs. 2.8 (2.3-4.7) Hz, p<0.0001]. DH correlated significantly with Fres (rs=-0.604, p<0.0001), Ax (rs=-0.652, p<0.0001), and several domains of the SGRQ and CAT scores. In the multivariate regression analysis, Fres and Ax explained 49% of the variability in DH. In conclusion, our results show that patients with COPD and DH have more altered RO. In these patients, the more pronounced the DH, the worse the RO parameters, the greater the symptom impact, and the more deteriorated the quality of life. Furthermore, SAD is a significant predictor of DH in this patient population.