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

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.

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.

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.

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.