Reproducibility of inspiratory muscle endurance testing using PowerBreathe for COPD patients

Assessing the strength and endurance of respiratory muscles is fundamental for characterizing respiratory muscle dysfunction. Although a variety of tests are used to evaluate respiratory muscle endurance, not all of them are applicable in clinical practice. Assessments can be made using a practical device called PowerBreathe®, but its reproducibility has not been tested in chronic obstructive pulmonary disease (COPD) patients.

To verify the reproducibility of the inspiratory muscle endurance test using a manometer and PowerBreathe® in COPD patients.

A cross-sectional study was used. In total, 19 moderate-severe COPD patients, male and female, aged 50 to 80 years took part in the research. This evaluation consisted of 2 tests: an incremental test and a constant one held on the same day and repeated after 48 hr. The incremental test started with 10-cm H₂ O, adding 10-cm H₂ O every 2 min and taking 1 min of rest before increasing the load. The highest load that could be sustained for at least 1 min was considered the sustained maximum inspiratory pressure (SMIP) value. The constant test was performed at an intensity of 80% of the SMIP and the maximum time limit was 30 min.

In the incremental test, there was a significant increase in the SMIP compared to the test-retest (61 ± 24/64.7 ± 23.8; p = .015); the value of the relative reproducibility was 0.96, the standard error of the absolute measurement was 4.7 (95% confidence interval 9.2), and the minimum detectable difference was 10.9. In the Bland-Altman analysis, the mean error was 4.2 (confidence interval -7.6 to 16.1). The constant test was not reproducible.

It was observed that the incremental test was reproducible to evaluate inspiratory muscle endurance in COPD patients. Furthermore, 2 tests needed to be carried out due to the learning effect.