OBJECTIVES: To evaluate heart rate variability (HRV), hemodynamics, mechanics, dyspnea and blood gases following different mechanical ventilation (MV) settings. BACKGROUND: No study has evaluated physiological changes during T-piece trials following different MV settings. METHODS: In 8 COPD patients on prolonged MV we applied in random order two MV settings: i) pressure support (PS) 20 cm H2O + positive end-expiratory pressure (PEEP) 0 cm H2O (setting-1) and ii) PS 15 cm H2O + PEEP 5 cm H2O (setting-2), each followed by a 30 min T-piece trial. RESULTS: Setting-1 induced greater minute ventilation, tidal volume/inspiratory time and lower pulmonary artery occlusion pressure; setting-2 reduced intrinsic PEEP. Mechanics and hemodynamics data did not differ, but all HRV time domain indices were reduced only after setting-1, suggesting a decreased parasympathetic and increased sympathetic cardiac modulation. CONCLUSIONS: The T-piece trial following setting-2 seems less stressful on neural control of HRV. Future studies on T-piece trials should consider the residual effect of the MV setting.