Background: There are several reports showing that expiratory muscle strength and endurance can be impaired in patients with COPD. This muscle weakness may have clinically relevant implications. Expiratory muscle training tended to improve cough and to reduce the sensation of respiratory effort during exercise in patients other than those with COPD.
Methods: Twenty-six patients with COPD (FEV1 38% predicted) were recruited for the study. The patients were randomized into two groups: group 1, 13 patients were assigned to receive specific expiratory muscle training (SEMT) daily, six times a week, each session consisting of 1/2 h of training, for 3 months; and group 2, 13 patients were assigned to be a control group and received training with very low load. Spirometry, respiratory muscle strength and endurance, 6-min walk test, Mahler baseline dyspnea index (before), and the transitional dyspnea index (after) were measured before and after training.
Results: The training-induced changes were significantly greater in the SEMT group than in the control group for the following variables: expiratory muscle strength (from 86 ± 4.1 to 104 ± 4.9 cm H2O, p < 0.005; mean difference from the control group, 24%; 95% confidence interval, 18 to 32%), expiratory muscle endurance (from 57 ± 2.9% to 76 ± 4.0%, p < 0.001; mean difference from the control group, 29%; 95% confidence interval, 21 to 39%), and in the distance walked in 6 min (from 262 ± 38 to 312 ± 47 m, p < 0.05; mean difference from the control group, 14%; 95% confidence interval, 9 to 20%). There was also a small but not significant increase (from 5.1 ± 0.9 to 5.6 ± 0.7, p = 0.14) in the dyspnea index.
Conclusions: The expiratory muscles can be specifically trained with improvement of both strength and endurance in patients with COPD. This improvement is associated with increase in exercise performance and no significant change in the sensation of dyspnea in daily activities.