Is inspiratory muscle training alone or in combination with pulmonary rehabilitation effective for the treatment of chronic obstructive pulmonary disease (COPD)?
Inspiratory muscle training improves symptoms, physical fitness, and quality of life in patients with COPD. When combined with pulmonary rehabilitation, inspiratory muscle training makes no difference compared with pulmonary rehabilitation alone.1 (Strength of Recommendation: B, inconsistent or limited-quality patient-oriented evidence.)
Primary care physicians treat approximately 80% of patients with COPD in the United States.2 Pulmonary rehabilitation is an individualized, supervised program incorporating physiotherapy, nutritional and psychosocial care, and limb training. The Global Initiative for Chronic Obstructive Lung Disease guideline recommends pulmonary rehabilitation because it improves symptoms, exercise capacity, and quality of life across all grades of COPD severity. Inspiratory muscle training uses targeted exercises and devices to increase the strength and endurance of the diaphragm and intercostal muscles because weakness of inspiratory muscles is associated with dyspnea and respiratory failure in COPD.3 Inspiratory muscle training is not typically included in pulmonary rehabilitation. The authors of the Cochrane review sought to determine if inspiratory muscle training alone or in combination with pulmonary rehabilitation can improve symptoms of COPD.
This Cochrane review included 55 randomized controlled trials (RCTs) and 2,467 patients.1 The studies were divided into two arms: pulmonary rehabilitation with inspiratory muscle training vs. pulmonary rehabilitation alone (22 RCTs; 1,446 participants) and inspiratory muscle training vs. control or sham (37 RCTs; 1,021 participants). The studies addressed pulmonary rehabilitation and inspiratory muscle training for interventions in COPD management. Participants were 44 years and older with stable COPD as diagnosed by the Global Initiative for Chronic Obstructive Lung Disease criteria.
Validated assessment tools were used to determine the effects on three primary outcomes: dyspnea, functional exercise capacity, and health-related quality of life. With these continuous data, the mean difference (MD) was used to analyze the size of the treatment effect: 0.2 represented a small effect, 0.5 was a medium effect, and 0.8 was a large effect. The tools used in the analysis for dyspnea were the Borg scale, the modified Medical Research Council dyspnea scale and the Baseline Dyspnea Index, and Transition Dyspnea Index. The measure for functional exercise capacity was the six-minute walk test, and the clinically significant measure for health-related quality of life was the COPD Assessment Test. The authors assessed the risk of bias in the included studies. Adverse effects were not reported.
When comparing inspiratory muscle training plus pulmonary rehabilitation to pulmonary rehabilitation alone, there was little to no difference in the scores of each of the three primary outcomes. However, inspiratory muscle training alone improved dyspnea compared with control or sham on the Baseline Dyspnea Index and Transition Dyspnea Index (MD = 2.98; 95% CI, 2.07 to 3.89; eight RCTs; 238 participants; very low-certainty evidence). Patients treated with inspiratory muscle training also demonstrated improvement in functional exercise capacity compared with control or sham, with an increase of 35.71 meters (95% CI, 25.68 to 45.74; 16 RCTs; 501 participants; moderate-certainty evidence) on the six-minute walk test. Inspiratory muscle training improved health-related quality of life (MD = −2.97; 95% CI, −3.85 to −2.10; two RCTs; 86 participants; moderate-certainty evidence) on the COPD Assessment Test, where any decrease in the test score represents a decrease in overall symptoms of COPD. The other assessments for health-related quality of life and inspiratory muscle strength found statistically significant improvement, but the clinical significance of these changes is questionable because of the risk of bias.
Limitations of the studies included heterogeneity in pulmonary rehabilitation and inspiratory muscle training and the significant risk of bias within the included studies. Sources of bias were a lack of allocation concealment and a lack of blinding.
There are no guidelines recommending inspiratory muscle training in addition to pulmonary rehabilitation. This Cochrane review supports current respiratory society statements regarding pulmonary rehabilitation, which conclude that “[inspiratory muscle training] used in isolation does confer benefits across several outcome areas,” but “its added benefit as an adjunct to exercise training in COPD is questionable.”4
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