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

Abstract

Among patients with chronic obstructive pulmonary disease (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). The effects of 8 wk 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 ± 19% predicted; Pi = -59 ± 14 cmHO; cycle ergometer peak work rate = 47 ± 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) decreased ( P < 0.05) with no significant change in ventilation, tidal inspiratory pressures, breathing pattern, or operating lung volumes during exercise. In conclusion, IMT improved inspiratory muscle strength and endurance in mechanically compromised patients with COPD and low Pi. The attendant reduction in EMGdi/EMGdi helped explain the decrease in perceived respiratory discomfort despite sustained high ventilation and intrinsic mechanical loading over a longer exercise duration. NEW & NOTEWORTHY In patients with COPD and low maximal inspiratory pressures, inspiratory muscle training (IMT) may be associated with improvement of dyspnea, but the mechanisms for this are poorly understood. This study showed that 8 wk of home-based, partially supervised IMT improved respiratory muscle strength and endurance, dyspnea, and exercise endurance. Dyspnea relief occurred in conjunction with a reduced activation of the diaphragm relative to maximum in the absence of significant changes in ventilation, breathing pattern, and operating lung volumes.

Dyspnea in COPD: New Mechanistic Insights and Management Implications

“…In a recent study Langer et al [96] showed that supervised IMT in patients with severe COPD and baseline inspiratory muscle weakness was associated with increased inspiratory muscle strength, reduced dyspnea, and improved exercise tolerance compared with sham training (Fig. 7).…”

Intolerance to and limitations of inspiratory muscle training in patients with advanced chronic obstructive pulmonary disease: A report of two cases

“…As the inspiratory muscles might become already trained [ 22 ], IMT is not effective in patients with COPD and high MIP (inspiratory muscle function > 60 cmH 2 O) [ 6 ]. Moreover, earlier studies showed that IMT induced respiratory muscle strength and deeper breathing, reduced f R, and contributed to dyspnea relief and the improvement of exercise tolerance in patients with COPD and maintained BMI [ 13 ]. Hence, IMT had been hypothesized to improve dynamic hyperinflation by reinforcing inspiratory muscles [ [8] , [9] , [10] ].…”

“…From the observations abovementioned, IMT might change a breathing pattern other than dynamic hyperinflation and subsequently affect exercise tolerance in patients with COPD. Given that IMT activates inspiratory muscles and induces deeper breathing [ 12 , 13 ], we hypothesized that the improvement of exercise tolerance might be depended on the degree of ventilatory efficiency obtained from IMT.…”

Locomotor Muscles in COPD: The Rationale for Rehabilitative Exercise Training

“…Consequently, participation in pulmonary rehabilitation is recommended as a pivotal intervention in symptomatic COPD regardless the severity of resting functional impairment . Beneficial changes in "respiratory responses" such as exertional ventilation (O'Donnell et al, 1998;Porszasz et al, 2005;Puente-Maestu et al, 2006), breathing pattern (O'Donnell et al, 1998), operating lung volumes (Porszasz et al, 2005;Puente-Maestu et al, 2006) and static respiratory muscle strength (Charususin et al, 2018;Langer et al, 2018) have been reported after training. These changes are, however, not particularly large and frequently inconsistent (Neder et al, 2019).…”