Inspiratory muscle training, with or without concomitant pulmonary rehabilitation, for chronic obstructive pulmonary disease

Chronic obstructive pulmonary disease (COPD) is a respiratory condition characterized by different degrees of airway blockage, causing dyspnea, cough with or without sputum production, and wheezing. It includes chronic bronchitis and emphysema. Risk factors are well known and lie mainly in tobacco smoking and air pollution. This condition is responsible for 3 million deaths worldwide in 2019, the majority of which are in low- and middle-income countries, making it the third cause of death worldwide.

COPD also affects people’s quality of life, physical activity, and normal participation in everyday activities, making it the seventh cause of poor health in terms of disability-adjusted life years. In this condition, air trapping and hyperinflation result in an increased burden on respiratory muscles. In this scenario, inspiratory muscle training (IMT) aims to improve inspiratory muscle strength and endurance, improving symptoms and performance. Different devices are used in IMT training, such as threshold-loading devices, passive and electronic flow-resistive devices, and isocapnic-hyperpnea devices. Current guidelines recommend starting pulmonary rehabilitation (PR) during hospitalization or right after discharge, and an optimal duration for a PR program is eight weeks. PR is a multilevel intervention consisting of physiotherapy, nutritional and psychosocial care, and patient-centered education. In some studies, it was demonstrated that IMT could be beneficial either alone or in combination with PR in patients with respiratory muscle weakness, but these effects are still unclear.

This review investigated whether inspiratory muscle training (IMT) either alone or together with pulmonary rehabilitation (PR) is helpful and safe in patients with COPD.

This review is important for

People with COPD, their loved ones/caregivers, health professionals caring for this population, general practitioners, researchers, and policymakers.

Outcomes of this review

This is a new Cochrane Systematic Review (CSR) published in 2023. The outcomes analyzed were dyspnea; functional exercise capacity; health-related quality of life; strength of inspiratory muscles, together with measures of respiratory muscle endurance and respiratory function; laboratory exercise tests mainly focusing on maximal oxygen uptake (VO2peak); and adverse events.

The CSR included 22 studies with 1,446 participants, which compared exercise together with IMT to exercise alone; and 37 studies with 1,021 participants that compared IMT to no training or sham device. The studies were published and/or registered up to October 20, 2022, and lasted from two weeks to a year. IMT protocols varied widely across the studies.

Results showed that PM plus IMT, compared to PM alone, probably makes little to no difference to dyspnea, inspiratory muscle strength, and quality of life; it is uncertain whether it improves functional exercise capacity. On the other hand, IMT alone compared to no training or sham device may reduce dyspnea assessed at one scale, but it is uncertain if assessed with others. Similarly, it probably improves quality of life when measured with one scale. Furthermore, IMT probably improves physical fitness and may make little to no difference in breathing muscles’ strength.

These results must be interpreted with caution because (i) most trials excluded patients who were not hospitalized and have not experienced exacerbation for a couple of weeks prior to the trial, thus the results may not be applicable to hospitalized cases just after an acute exacerbation. (ii) Most studies that looked at the combined effect of PR plus IMT did not include patients with reduced maximal inspiratory pressure (PImax), making the results not applicable in cases of severe COPD that require long-term oxygen therapy. (iii) Only three studies employed endurance training. (iv) There was a wide variation in PR and IMT protocols. (v) Some studies had serious concerns about imprecision and inconsistency, as well as a high risk of blinding bias, leading to an overall quality of evidence for all outcomes ranging from very low to moderate.

Author’s conclusion of the review

Inspiratory muscle training (IMT) combined with pulmonary rehabilitation (PR) may not have an additional benefit on dyspnea, functional exercise capacity, and health-related quality of life, whereas there was an improvement in inspiratory muscle strength and endurance, although it was not clinically relevant. On the other hand, IMT compared to sham or no intervention may decrease dyspnea and increase functional-exercise capacity and health-related quality of life. This intervention may also improve inspiratory muscle strength and endurance, although the clinical relevance of this intervention was doubtful since it was not standardized. For both comparisons, the authors could not determine a possible larger effect in participants with respiratory muscle weakness and with longer durations of training.

Future recommendations

The authors recommended that further studies are needed, particularly to clarify (a) the potential benefit of PR combined with IMT on patients with respiratory muscle weakness, which currently was not found. (b) Larger sample sizes are needed in particular to find out the greater possible effect on patients with respiratory muscle weakness and (c) to compare the different IMT protocols. (d) Moreover, further studies should address the possible use of IMT for patients who are unable to practice PR. The authors recommend (e) a sham IMT for the control group to reduce the overestimation of subjective outcomes. Furthermore, the authors advise (f) training with a high inspiratory flow rate and at volumes close to total lung capacity to improve performance in hyperinflated COPD patients. (g) Finally, further studies should address the difference between training loads and threshold IMT with endurance IMT.

by Robin Kuruvila Sentinella