Longitudinal lung volume changes in patients with chronic obstructive pulmonary disease

Background: The progression of lung hyperinflation in patients with chronic obstructive pulmonary disease (COPD) has not been studied in a long-term prospective cohort. We explored the longitudinal changes in lung volume compartments with the aim of identifying predictors of a rapid decline of the inspiratory capacity to total lung capacity ratio (IC/TLC). Methods: The study population comprised 324 patients with COPD who were recruited prospectively. Annual rates of changes in pulmonary function, including forced expiratory volume in 1 s (FEV₁), forced vital capacity (FVC), total lung capacity (TLC), functional residual capacity (FRC), residual volume (RV), vital capacity (VC), IC, and IC/TLC, were estimated using the random coefficient models. Results: The mean annual rates of changes in pre- and post-bronchodilator FEV₁ were -23.0 mL/year (p < 0.001) and -26.5 mL/year (p = 0.004). The mean annual rates of changes in VC, IC, TLC, and IC/TLC were -33.7 mL/year (p = 0.007), -53.9 mL/year (p < 0.001), -43.7 mL/year (p = 0.012), and -0.65 %/year (p = 0.001), respectively. RV, FRC, and RV/TLC did not change significantly during the study period. Multivariate logistic regression analysis showed that a high modified Medical Research Council (MMRC) dyspnea scale score, a high Charlson comorbidity index value, and low post-bronchodilator FEV₁ were associated with rapid decline in IC/TLC. Conclusion: MMRC dyspnea scale, post-bronchodilator FEV_1, and the Charlson comorbidity index at baseline were independent predictors of a rapid decline in IC/TLC.