Gas distribution in a two-compartment model during volume or pressure ventilation : role of elastic elements

The results of the studies on pulmonary gas distribution during constant-flow controlled-volume inflation (VCV) and inspiratory constant pressure inflation (PCV) in experimental studies are conflicting. In a mathematical model, with the characteristics of two lung compartments including tissue viscoelastic properties, pulmonary gas distribution was tested by simulating PCV and VCV at same inflation volumes. The compartmental distributions of the tidal volume were compared during CMV and PCV in different configurations obtained by changing the elastic and viscoelastic properties in each compartment, but maintaining the same total values of respiratory mechanics measured in patients. In all instances PCV resulted in a slightly higher air-trapping than in VCV mode. Heterogeneous elastic properties diverted most of the tidal volume towards the less compromised compartment. However, both ventilatory modes provided similar compartmental gas distribution, but during VCV compartmental peak pressures were higher in the sicker compartment respect to PCV. The use of PCV could grant a less remarkable pressure variability able to reduce the potential ventilator-associated lung injury. Moreover, the parameters measured during an end-inspiratory pause could not pinpoint unique characteristics for each configuration.