Abstract
Chronic obstructive pulmonary disease (COPD) is characterized by persistent airflow limitations, occurring mainly in the small airways. Weakness in the respiratory muscles contributes to dyspnea and a decreased exercise capacity in COPD patients. This study aimed to investigate the effectiveness of home-based inspiratory muscle training (IMT) on small airway function and symptoms in COPD patients. This research adopted a non-randomized controlled-study quasi-experimental design. The IMT program consisted of two 15 min sessions·d(-1), 5 d·wk(-1), with 40% of the maximal inspiratory pressure (PI(max)) on each participant's assessment results and lasted for 12 weeks. Small airway function was assessed using plethysmography at baseline and after 12 weeks. The modified British Medical Research Council (mMRC), COPD assessment test (CAT), PI(max), and 6 min walking distance (6MWD) were recorded at baseline as well as four, eight, and twelve weeks. Twenty-three participants with at least moderate COPD were enrolled in IMT (n = 16) or in the control group (n = 7) in this study. The study participants were mostly male (82.6%), and the average age was 68.29 ± 10.87 years, with a mean body mass index (BMI) of 23.54 ± 4.79. After 12 weeks, the ratios of the first second of forced expiration to the forced vital capacity (FEV(1)/FVC%) (B coefficient [95% Wald confidence interval] of 5.21 [0.46 to 9.96], p = 0.032), forced expiratory flow (FEF(25-75%)) (0.20 [0.04 to 0.35] L/s, p = 0.012), and FEF(50%) (0.26 [0.08 to 0.43] L/s, p = 0.004) in the IMT group were significantly better than in the control group. The IMT group showed significantly lower CAT scores at week 8 (-5.50 [-10.31 to -0.695] scores, p = 0.025) than the control group. The mMRC grade, CAT score, PI(max), and 6MWD were significantly improved compared to their values at baseline in the IMT group. Home-based IMT effectively improved post-bronchodilator small airway function and disease-associated symptoms in COPD patients.