Background: Pursed-lips breathing (PLB) is able to modify muscular recruitment and may influence diaphragm mobility in chronic obstructive pulmonary disease (COPD) patients Aim: To evaluate acute effects of PLB on chest wall volumes and diaphragm mobility in COPD subjects. Methods: A randomized, controlled, single-blind crossover trial in moderate-severe COPD subjects. Anthropometry and lung function were collected before study protocol. Chest wall and its compartments (pulmonary rib cage (VRCp), abdominal rib cage (VtRCa) and abdominal (VtAB)) were assessed by optoeletronic plethysmography (OEP). Diaphragm mobility was evaluated by ultra-sound. Data were collected before and after breathing pattern (with or without PLB). Results: We assessed 13 patients (9 M), II-IV GOLD statement, 65.4±7.6 years, BMI 23.9±3.08 Kg/m2, FEV₁/FVC(%) 63.1±13.6, FEV₁(%) 39.8±11.9, PImáx 71.7± 27.13, PEmáx 81.0±24.5. After PLB, we observed statistical increase on tidal volume (Vt) of VRCp, VtRC, VtAB, respiratory cycle total time, inspiratory time, expiratory time, respiratory rate and inspiratory flow (p< 0.001 for all variables).There was no significant difference on diaphragm mobility before and after PLB (p>0.05). Conclusion: PLB improves chest wall volumes by reducing respiratory cycle without diaphragm mobility enhance in COPD subjects.Figure 1: Diaphragm mobility with and without PLB in COPD patients.