Fig. 1

Difference between monitored tracheal pressure and aggregate alveolar pressure in flow-controlled ventilation (FCV). For calculating the dynamic compliance, the aggregate alveolar driving pressure (ΔP) has to be determined first by correcting the measured tracheal ΔP for the pressure drop across the airway resistance. Averaged data provided in [1] are used. Depending on regionally different resistances, also regional alveolar ΔP and dynamic compliance may be different. Because the overall lung–chest system can only be studied from the outside as a single functional unit, the calculations necessarily represent aggregate estimates of the mechanical properties of the different compartments. The calculation is based on an I:E ratio of 1:1 (which is typical for FCV) and the assumption the measured resistance is entirely related to resistance in the airways. Hence tissue resistance is not considered, so the calculated pressure drop may be slightly overestimated and, in consequence, the aggregate alveolar ΔP somewhat underestimated