Mice were ventilated for six hours with the flexiVent ventilator (SCIREQ, Montreal, Canada). All mice survived the protocol. Mice were either ventilated with low tidal volume (lowV T ) of Figure 2 . Heart rate and blood pressure. Electrocardiogram (ECG) was recorded permanently. A. Heart frequency (HF) was calculated simultaneously from the ECG and is displayed in beats per minute (bpm). B. Mean arterial blood pressure (BP) was measured via a catheter in the carotid artery.(LowV T RM5 n = 6, highV T RM5 n = 6, lowV T noRM n = 5, highV T noRM n = 4, lowV T RM60 n = 5). doi:10.1371/journal.pone.0024527.g002 Figure 3 . Blood gas results. Arterial blood was analysed after six hours of ventilation. A. pO 2 /FiO 2 ratio was calculated, FiO 2 was 0.5. B. Comparison of pCO 2 levels. (LowV T RM5 n = 6, highV T RM5 n = 6, lowV T noRM n = 5, highV T noRM n = 4, lowV T RM60 n = 5). * p,0.05, ** p,0.01, *** p,0.001. doi:10.1371/journal.pone.0024527.g003 8 mL/kg and a frequency of 180 min 21 or high tidal volume (highV T ) of 16 mL/kg and a frequency of 90 min 21 , so that both groups received the same minute volume. The highV T group was ventilated with 3% CO 2 to maintain normocapnia without further decreasing ventilation frequency. The fraction of inspired oxygen (FiO 2 ) was 0.5 in all experiments. A positive end-expiratory pressure (PEEP) of either 2 cmH 2 O or 6 cmH 2 O was applied. One recruitment manoeuvre (RM) with 30 cmH 2 O pressure and six seconds duration was performed after onset of ventilation to open airspaces and standardize lung volume. Resistance, compliance and impedance of the lung were measured by the lowfrequency forced oscillation technique every ten minutes.