Abstract
Background: The Global Initiative for Chronic Obstructive Lung Disease guidelines (http://www.goldcopd.org, accessed January 16, 2020) reported the use of inspiratory muscle training (IMT) as a part of comprehensive respiratory rehabilitation programs for patients with chronic obstructive pulmonary disease (COPD). However, some studies have indicated that the effect of such training is uncertain. Moreover, it is unclear whether IMT effects are caused by improvement in central or peripheral factors. Few studies examining IMT effects have used new evaluation items. We aimed to clarify the effects of IMT by additionally measuring the airway-occlusion pressure at 0.1 s after the start of inspiratory flow (P0.1), as an index of respiratory central output, and by evaluating diaphragm movement based on the thickness of the diaphragm muscle (Tdi) using ultrasound.Methods: Thirteen patients with COPD participated in the study. IMT was performed using the POWER breathe® Medic Plus breathing trainer in combination with each participant’s outpatient rehabilitation regimen. Starting at 20% of the maximal inspiratory pressure (PImax) and increasing to 50%, the participants performed 30 IMT repetitions twice a day for 2 months. Respiratory muscle strength, P0.1, 6-min walking distance (6MWD), and Tdi were measured before and after IMT. Dyspnea, lower limb fatigue (assessed using the Borg Scale), and respiratory rate (RR) were measured before and after the 6-min walk test (6MWT). Results: PImax and 6MWD significantly increased after training. Tdi at resting inspiration and expiration and maximal inspiration also significantly increased after training. In addition, the Borg Scale scores for dyspnea and leg fatigue and the RR of the 1-min recovery period after the 6MWT significantly decreased. There was no significant difference in P0.1.Conclusions: We examined the combined effects of IMT, incorporating the evaluation of P0.1 and Tdi. We found that the PImax, 6MWD, and Tdi significantly increased, but no significant difference was observed in P0.1 after training. These results suggest that the effects of IMT may be attributed to the improved peripheral factors rather than to the central factors.