Under general anesthesia provided by ketamine 3.3 mg/Kg (Panpharma, France) and xylazine 1 mg/Kg (Rompun®, Bayer, Germany), a cuff tube of 2.5 mm (Mallinckrodt™, Covidien®, U.S.A.) was inserted through the mouth into the trachea under view control. The animal was connected to a volume-controlled respirator (Servo ventilator 900C, Siemens®, Germany) (tidal volume of 12 mL/Kg with zero end-expiratory pressure [ZEEP], a respiratory rate of 25 bpm and an 0.5 inspired fraction of O2). Rabbits were kept anesthetized and paralyzed throughout the experiment with midazolam (0.06 mg/Kg/h) (Hypnovel®, Roche, Switzerland) and cisatracurium besilate (0.3 mg/Kg/h) (Nimbex®, GlaxoSmithKline, U.K). Isotonic serum was infused.