Relative distribution of ZV and ZQ within ROI 1 to 4 for the left and right lung at baseline and following the application of PEEP 20. * denotes significant difference (p < 0.05) for ZQ compared with baseline. # denotes significant difference (p < 0.05) for ZV compared with baseline. Relative distribution given as a percentage. ZV = ventilation-induced change in thoracic impedance; dotted line. ZQ = perfusion-induced change in thoracic impedance; solid line. Region of interest (ROI) 1 = ventral; ROI 2 = mid-ventral; ROI 3 = mid-dorsal; ROI 4 = dorsal. BL = baseline; LL = left lung; PEEP20 = the application of 20 cmH2O of positive end-expiratory pressure; RL = right lung.