Respiratory muscle weakness and its association with exercise capacity in patients with chronic obstructive pulmonary disease

Abstract

Introduction: Although COPD patients commonly present respiratory complaints despite pharmacological treatment, dyspnea does not correlate directly and linearly with spirometric data, a fact that makes it difficult to select patients for pulmonary rehabilitation. Thus, seems logical that the measurement of respiratory muscle strength could help in this initial assessment if it presents a good correlation with exercise capacity. The aim of this study is to assess whether patients with muscle weakness, characterized as a reduction in maximal inspiratory pressure (PImax) below 70% of predicted value, have a good relationship between the assessed respiratory muscle strength and the exercise capacity measured by the 6-min walk test (6MWT) in patients with COPD.

Methods: Patients diagnosed with COPD according to the 2019 Global Initiative for Chronic Obstructive Lung Disease (GOLD) on regular use of their medications, without exacerbations for 3 months or more and with respiratory muscle weakness (PImax < 70% of predicted) performed 6MWT in a 30-m-long flat corridor.

Results: Data from 81 patients were analyzed. There was a strong correlation between the distance of the 6MWD with the PImax (r = 0.764, p < 0.0001). When separating the sample by the 350-m cut in the 6MWD, we found that the patients with the worst performance in the test are those who present the greatest respiratory muscle weakness.

Conclusion: PImax correlates well with exercise capacity, and patients with respiratory muscle weakness could be referred to a pulmonary rehabilitation protocol tied to inspiratory muscle training.

Keywords: COPD; exercise capacity; muscle weakness; respiratory exercise; respiratory muscles.