Regional lung function and heterogeneity of specific gas volume in health and emphysema

To study regional lung function by standard CT and characterize regional variations of density and specific gas volume (SVg) between different lung volumes, we studied 10 healthy and 10 severe emphysematous subjects. Correspondent CT images taken at high and low lung volumes were registered by optical flow to obtain 2-D maps of pixel-by-pixel differences of density (HU) and SVg (SVg) at slice levels near the aortic arch, carina and top diaphragm. . Published on August 9, 2012 as doi: 10.1183/09031936.00050112 ERJ Express Copyright 2012 by the European Respiratory Society. In healthy subjects, HU was higher at all levels (p<0.001) with higher variability expressed as interquartile range (p<0.001) largely due to its differences between dorsal and ventral regions. In patients, median SVg values were 3.2 times lower than healthy volunteers (p<0.001), while heterogeneity of SVg maps, expressed as quartile coefficient of variation, was 5.4 times higher (p<0.001). In all patients there were areas with negative values of SVg. In conclusion, SVg is uniform in healthy lungs and minimally influenced by gravity. The significant SVg heterogeneity observed in emphysema allows to identify areas of alveolar destruction and gas trapping and suggests that SVg maps provide useful information for evaluation and planning of emerging treatments that target trapped gas for removal.