Inspiratory muscle training reduces respiratory neural drive (RND) during exercise in patients with COPD

Mechanisms for improvements in dyspnea after inspiratory muscle training (IMT) have not been systematically studied. We investigated whether this might be ascribed to reductions in RND. Ten clinically stable patients with COPD (FEV 1 :61±20%pred.) with activity related dyspnea (Baseline Dyspnea Index:6.0±1.3) and inspiratory muscle weakness (Pi,max: 61±12cmH 2 O) were randomized into an intervention group (n=7), or a control group (n=3). Before and after an 8-week daily IMT program, an endurance cycling test was performed at 75% peak work rate. Patients rated dyspnea during exercise an a Borg CR-10 scale and diaphragm electromyography (EMGdi) was assessed with a multipair esophageal electrode catheter (Luo, Y.M. et al. Clin Sci 2008;115:233-44). IMT intensity either increased from 68±11% to 123±21% baseline Pi,max (intervention) or remained constant at 8±2% baseline Pi,max (control). Larger increases in Pi,max (28±13 vs 10±3cmH 2 O; p=0.009) and reductions in RND (-12±6% vs 3±11% EMGdimax; p=0.023; Figure) at standardized ventilation were observed in the intervention group. This was associated with larger improvements in endurance time (356±265sec vs 17±38sec; p=0.014; Figure) and dyspnea at standardized ventilation (-3.3±2.6 vs -0.3±0.6 Borg units; p=0.023). IMT decreases RND during exercise and this might be mechanistically related to improvements in dyspnea and exercise tolerance in selected patients with COPD.