Fig. 2. Intraabdominal and intrathoracic caval vein pressure and gastric pressure (top ) during intraperitoneal carbon dioxide insufflation at baseline (open symbols) and during different insufflation pressures (closed symbols). Corresponding differences between gastric pressure and intrathoracic caval vein pressure (middle ) illustrates the transition (arrow) from a zone 3 abdominal condition (shaded zone) to a zone 2 condition with increasing intraperitoneal pressure. Transmural intrathoracic caval vein pressure (bottom ) also is shown. The data are the mean ± SD from eight anesthetized, mechanically ventilated patients undergoing intraperitoneal carbon dioxide insufflation. *P < 0.05 versus  group baseline; #P < 0.05 versus  group desufflation; §P < 0.05 versus  10 mmHg insufflation pressure.