Description of one given experimental condition. During the first five minutes the experimental step, either change in tidal volume or positive end-expiratory pressure (PEEP), is applied without any measurement and continued up to the end of this phase. Then positron emission tomography (PET) transmission scan is taken for 10 minutes followed by a five-minute wash-in phase. Afterwards, 13N-N2 positron-emitting tracer is washed-out for five minutes. In-between the amount of the tracer entering the lung is measured (entry function). PET emission scans are then performed at tracer equilibrium and during tracer wash-out. The electrical impedance tomography signals used in present analysis are recorded for one minute at the end of both transmission and emission periods (black squares). Each step lasts 30 minutes.