Figure 2b. Graphs show mean attenuation values as a function of cephalocaudal lung level in (a) prone and (b) supine groups. In normal lung, mean attenuation increased gradually from apex to base. At baseline after oleic acid injection, mean attenuation increased at all levels, and line became steeper than that of normal lung. In prone group (a), prone positioning reversed relationship between mean lung attenuation and cephalocaudal lung height. In prone position, mean attenuation reached maximum at 10 cm above diaphragm and decreased toward the base, thus generally decreasing from apex to base. Repositioning to supine restored cephalocaudal gradient of mean attenuation to similar pattern of baseline. However, slope became gentler than baseline. In supine group (b), graph shows similar pattern to that of baseline. DD = dome of diaphragm.