Fig. 3. Percentage of total tidal variation per region of interest. The stacked bars illustrate the changes in the ventilation distribution across the four regions of interest (ROI; also see table 3). The spontaneous breathing (SB) group is uniform throughout the case, whereas the pressure control (PCV) and pressure support (PSV) groups exhibit an increase in ventilation in ROI 3 and 4 and a decrease in ROI 2 at time-points BEGIN and END, indicating a ventral shift in the ventilation. ROI 2, 3, and 4 in the SB group are significantly different from those in groups PCV and PSV (P < 0.05; MANCOVA with Sidak adjustment). AWAKE = before the induction of anesthesia; BEGIN = after the placement of the laryngeal mask airway; END = before the end of anesthesia; PACU = after arrival in the postanesthesia care unit.