Regional variability of sequential ventilation without and with positive end-expiratory pressure (PEEP). A) 0 cmH2O PEEP; B) 8 cmH2O PEEP. Figures on the left are box plots of the logarithm of the ratio of relative ventilation at 12 ml/kg tidal volume to relative ventilation at 6 ml/kg tidal volume (log V12/V6) by lung region for one representative animal. The box defines the inter-quartile range with a line indicating the median value. Whiskers indicate the plausible range of data with potential outliers identified as individual points. Figures on the right are 3-dimensional reconstructions of the lungs viewed from a lateral position. Red boxes indicate a 10% or greater increase and blue boxes represent a 10% or greater decrease in relative ventilation at 12 ml/kg compared with 6 ml/kg tidal volumes. White boxes represent regions with < 10% change in relative ventilation with tidal volume change. Inset: Lung Divisions: Each lung was divided into five regions. The first region included all lung pieces in all ventral-dorsal sections that were adjacent to the diaphragm at any point. The remaining lung was divided into four regions as indicated based on bisecting transverse and coronal planes.