Airways opening pressure during PEEP step change test. Upper panel: airways opening pressure (Pao) during the entire PEEP step change test with PEEP-new during one in vivo experiment. The dashed white lines are the target PEEP. Lower panel: detail of Pao during the PEEP step change from 4 to 5 cmH2O. For this step, the arrows indicate the start of the PEEP step, the settling time, the overshoot and the target PEEP.