Quasistatic inflation pressure–volume curves of lung (A) and respiratory system (B) obtained after 4 h of spontaneous ventilation (continuous line in all panels), positive pressure mechanical ventilation (PPMV), and whole-body (NPWBMV) or thorax-only negative pressure ventilation (NPTOMV). PL and Prs, transpulmonary pressure and pressure across the respiratory system, respectively. Both for PL– and Prs–volume curves, no significant difference was found among groups (P = 0.628 and P = 0.542, respectively). Bars: SD.