The Effectiveness of Home-Based Inspiratory Muscle Training on Small Airway Function and Disease-Associated Symptoms in Patients with Chronic Obstructive Pulmonary Disease

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 (FEV₁/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.

Keywords: chronic obstructive pulmonary disease; dyspnea; home-based pulmonary rehabilitation; inspiratory muscle training; small airway function.

Figure 1

The threshold IMT device.

Figure 2

Flow diagram from enrolment to analysis process of the study.

Figure 3

Changes in lung function from baseline to 12 weeks in the IMT and control groups. The interactions between two groups and the change from T1 (baseline) to T4 (12 weeks) were compared and analyzed through GEE. (a) The forced expiratory volume in 1-second-to-vital-capacity ratio (FEV1/FVC%). (b) Forced expiratory flow between 25 and 75% of the forced vital capacity (FEF_25–75%). (c) Forced expiratory flow at 50% of the forced vital capacity (FEF_50%). * p < 0.05 and ** p < 0.01.

Figure 4

Changes in disease-associated symptoms from baseline to 12 weeks in the IMT and control groups. The interactions between two groups and the change achieved between time points were compared and analyzed through GEE. The differences in the IMT group between T2 (4 weeks), T3 (8 weeks), and T4 (12 weeks) vs. T1 (baseline) were analyzed through Wilcoxon signed-rank test. (a) Modified British Medical Research Council (mMRC) dyspnea index. (b) COPD assessment test (CAT) scores. (c) Maximal inspiratory pressure (PImax). (d) The 6 min walking distance (6MWD). * p < 0.05 through GEE, † p < 0.05, and ‡ p < 0.01 vs. T1.

Figure 5

Changes in resting heart rate (RHR) from baseline to 12 weeks in the IMT and control groups. The interactions between two groups and the change between time points (from T1 to T2 (4 weeks), T3 (8 weeks), or T4) were compared and analyzed through GEE. ** p < 0.01 and *** p < 0.001. The differences in the IMT group at different time points vs. T1 were analyzed through Wilcoxon signed-rank test. † p < 0.05.