Fig. 6

Left panel: isolated lung, right panel: lung and chest wall. Tidal airway P/V curves (red arrows) and tidal lung (transpulmonary) P/V curves (blue arrows). In the isolated lung without a chest wall, the airway P/V curve is equal to the transpulmonary P/V curve. The tidal volume from the low PEEP was almost equal to the end-expiratory lung volume change between the ZEEP and a PEEP of 8 cmH₂O when the chest wall stiffness was normal and lung compliance was 38 ml/cmH₂O. The end-inspiratory transpulmonary pressure of the tidal volume from ZEEP is close to the end-expiratory transpulmonary pressure at PEEP of 8 cmH₂O. The lung P/V curves of the isolated lungs (red arrows, left panel) are identical to the lung P/V curves (blue arrows, right panel) of the complete model (lung, chest wall and abdomen) in the right panel. The end-inspiratory airway pressure of a tidal volume from ZEEP is right shifted from the end-expiratory airway P/V point of PEEP 8 cmH₂O due to the influence of the chest wall with a pressure equal to the change in pleural pressure (ΔPPL). Note that the lung P/V curves have been transpositioned in parallel from its actual starting point at ≈5 cmH₂O to zero in order to visualize that the slope of the lung P/V curve is identical to the slope of the end-expiratory airway P/V points (for the actual position of lung P/V curves, see Fig. 7)