Diaphragmatic excursion is correlated with the improvement in exercise tolerance after pulmonary rehabilitation in patients with chronic obstructive pulmonary disease

BACKGROUND: In patients with chronic obstructive pulmonary disease (COPD), the maximum level of diaphragm excursion (DE(max)) is correlated with dynamic lung hyperinflation and exercise tolerance. This study aimed to elucidate the utility of DE(max) to predict the improvement in exercise tolerance after pulmonary rehabilitation (PR) in patients with COPD. METHODS: This was a prospective cohort study. Of the 62 patients with stable COPD who participated in the outpatient PR programme from April 2018 to February 2021, 50 completed the programme. Six-minute walk distance (6MWD) was performed to evaluate exercise tolerance, and ultrasonography was performed to measure DE(max). Responders to PR in exercise capacity were defined as patients who demonstrated an increase of > 30 m in 6MWD. The receiver operating characteristic (ROC) curve was used to determine the cut-off point of DE(max) to predict responses to PR. RESULTS: Baseline levels of forced expiratory volume in 1 s, 6MWD, maximum inspiratory pressure, DE(max) and quadriceps muscle strength were significantly higher, and peak dyspnoea of modified Borg (mBorg) scale score was lower in responders (n = 30) than in non-responders (n = 20) to PR (p < 0.01). In multivariate analysis, DE(max) was significantly correlated with an increase of > 30 m in 6MWD. The area under the ROC curve of DE(max) to predict responders was 0.915, with a sensitivity and specificity of 83% and 95%, respectively, at a cut-off value of 44.9 mm of DE(max). CONCLUSION: DE(max) could adequately predict the improvement in exercise tolerance after PR in patients with COPD.