Changes in tidal volume at different time points during the ventilation protocol. Results are presented as means ± standard deviation. n = 7, 6 and 5 animals for HiP-C, HiP-Met and LoP groups, respectively. *P < 0.05 for HiP groups vs. LoP groups. LoP-C: low pressure-no metformin; LoP-Met: low pressure-metformin; HiP-C: high pressure-no metformin; HiP-Met: high pressure-metformin.