Patients' two lungs (TLV) will be mechanically ventilated with a pressure-controlled ventilation mode, a fraction of inspired oxygen (FiO2) of 0.4 in air, TV of 8 mL kg-1 (predicted body weight (PBW)), inspiratory to expiratory (I: E) ratio of 1:2.5 and PEEP of 5 cm H2O, fresh gas flow (FGF) of 1.5-1.7 L min-1, and RR adjusted to achieve a PaCO2 of 35-45 mm Hg.