Figure 3.

Esophageal pressure tracing at different balloon filling. In case of an underfilled balloon (A), both baseline level and tidal swing of Pes are underestimated. Optimal balloon filling volume (B) is the smaller volume associated with the largest tidal increase of Pes; baseline Pes may be increase compared to pleural pressure due to the elastance of the esophagus. In case of balloon overfilling (C), a sudden and important increase of baseline is observed due to the elastic recoil of an overstretched balloon wall; moreover, heart noise usually increases whereas tidal swing of Pes may decrease. Pes, esophageal pressure.