Enhanced diaphragm excursion and exercise tolerance in chronic obstructive pulmonary disease patients through inspiratory muscle training after standardized pulmonary rehabilitation: randomized controlled trial

<bold>Objective:</bold> Inspiratory muscle training (IMT) is used to improve inspiratory muscle strength in patients with chronic obstructive pulmonary disease (COPD). However, the effect of IMT on diaphragmatic function has not yet been thoroughly evaluated. This study aimed to evaluate the effect of IMT on maximum diaphragmatic excursion (DEmax) using ultrasonography in patients with COPD. <bold>Methods:</bold> This was a single-center, randomized, prospective, parallel-group, unblinded controlled trial involving 38 participants with stable COPD. Participants underwent a standardized 12-week pulmonary rehabilitation (PR) program followed by a 12-week IMT program, consisting of home-based IMT and low-frequency outpatient PR sessions supervised by physiotherapists (once every 2 weeks), vs low-frequency outpatient PR alone as a control. The DEmax and exercise tolerance were measured. <bold>Results:</bold> Out of the 38 patients initially enrolled in the PR program, 33 successfully completed it and were subsequently randomized to the IMT program. Finally, 15 (94%) and 14 (88%) patients from the IMT and control groups, respectively, completed the study. Following the IMT program, DEmax increased in the IMT group (50.1 ± 7.6 mm to 60.6 ± 8.0 mm, p < 0.001), but not in the control group (47.4 ± 7.9 mm to 46.9 ± 8.3 mm, p = 0.10). Changes in DEmax and exercise tolerance (peak V’O₂) were greater in the IMT group than in the control group (both p < 0.01). <bold>Conclusions:</bold> IMT following the PR program improved DEmax and exercise tolerance. Therefore, DEmax may be an important outcome of IMT.