Fig. 2. For these plots, the lungs were divided into 10 sections of equal height along the dependent-to-nondependent distance. Normalized regional ventilation, blood flow, and ventilation-to-perfusion ratios per voxel were averaged within each section. Plotted values are the mean value across all individuals for each section; error bars illustrate SD for the individual values for each section. Values at the extremes of the dependent-to-nondependent distance are influenced by the edge effect (underestimation of the radiotracer concentration at the lung periphery). PEEP = positive end-expiratory pressure.