Eight-week high-intensity inspiratory muscle training improves cardiac autonomic function in COPD: a randomized...

Cardiovascular autonomic dysfunction and respiratory muscle weakness have been detected in patients with COPD. Although low-intensity inspiratory muscle training over 12 weeks increases cardiac parasympathetic (vagal) activity, eight-week programmes at the highest tolerable intensity and their effects on cardiovascular autonomic function remain untested.

Thirty-nine stable COPD patients were randomized to inspiratory muscle training or control. Both received standard care, excluding pulmonary rehabilitation; the training group additionally performed 30 breaths twice daily at the highest tolerable intensity for eight weeks using a tapered flow resistive loading device. Assessments comprised pulmonary and respiratory muscle function, heart rate variability (HRV), blood pressure variability, baroreflex sensitivity, dyspnoea, 6-min walk distance and health status. Thirty-seven participants (training n = 18, control n = 19) completed the protocol.

Maximal inspiratory pressure increased by 22.46 ± 15.71 cmH₂O (p < 0.001), and cardiac parasympathetic activity rose (high-frequency component of HRV: 36.99 ± 17.51% to 46.84 ± 15.33%, p < 0.01). Sympathetic index decreased (low-frequency component of HRV: 54.13 ± 21.40% to 40.73 ± 17.01%, p < 0.001), as did the low-frequency/high-frequency ratio (2.30 ± 2.39 to 1.10 ± 0.83, p < 0.01). Systolic blood pressure variability decreased significantly. Baroreflex sensitivity increased from 5.36 ± 3.15 to 7.18 ± 4.58 ms/mmHg but was not significant (p = 0.05). Six-minute walk distance improved from 347.47 ± 82.72 to 378.71 ± 80.09 m (p < 0.01), and health status improved (COPD Assessment Test 7.72 ± 3.36 to 3.61 ± 2.85; Clinical COPD Questionnaire 1.07 ± 0.52 to 0.48 ± 0.31; both p < 0.001). These training-group improvements significantly exceeded control; ANCOVA confirmed group effects after baseline adjustment.

Eight-week highest tolerable intensity inspiratory muscle training enhances cardiovascular autonomic function in COPD through increased parasympathetic and reduced sympathetic activity, and improves functional capacity and health status.