Inspiratory muscle training reduces diaphragm activation and dyspnea during exercise in COPD

Among patients with COPD, those with the lowest maximal inspiratory pressures experience greater breathing discomfort (dyspnea) during exercise. In such individuals, inspiratory muscle training (IMT) may be associated with improvement of dyspnea but the mechanisms for this are poorly understood. Therefore, we aimed to identify physiological mechanisms of improvement in dyspnea and exercise endurance following inspiratory muscle training (IMT) in patients with COPD and low maximal inspiratory pressure (Pi,max). The effects of 8 weeks of controlled IMT on respiratory muscle function, dyspnea, respiratory mechanics, and diaphragm electromyography (EMGdi) during constant-work rate cycle exercise were evaluated in patients with activity-related dyspnea (Baseline Dyspnea Index <9). Subjects were randomized to either IMT or a sham training control group (n=10 each). Twenty subjects (FEV= 47{plus minus}19 %predicted; Pi,max= -59{plus minus}14 cmHO; cycle ergometer peak work rate= 47{plus minus}21 %predicted) completed the study; groups had comparable baseline lung function, respiratory muscle strength, activity-related dyspnea and exercise capacity. IMT, compared with control, was associated with greater increases in inspiratory muscle strength and endurance, with attendant improvements in exertional dyspnea and exercise endurance time (all p<0.05). After IMT, EMGdi expressed relative to its maximum (EMGdi/EMGdi,max) decreased (p<0.05) with no significant change in ventilation, tidal inspiratory pressures, breathing pattern and operating lung volumes during exercise. In conclusion, IMT improved inspiratory muscle strength and endurance in mechanically compromised patients with COPD and low Pi,max. The attendant reduction in EMGdi/EMGdi,max helped explain the decrease in perceived respiratory discomfort despite sustained high ventilation and intrinsic mechanical loading over a longer exercise duration.

Publication year:2018

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BOF-publication weight:6

CSS-citation score:3

Authors:International

Authors from:Higher Education

Accessibility:Open