Differences in lung attenuation gradients between supine and standing positions in healthy participants on conventional/supine and upright computed tomography.

ABSTRACT

The effect of gravity on the lungs has been evaluated using computed tomography (CT) in the supine and prone positions but not the standing position. However, as humans spend most of the daytime in the standing position, we aimed to compare lung attenuation gradients between the supine and standing positions, and to assess the correlations between the lung attenuation gradients and participant characteristics, including pulmonary function test results. Overall, 100 healthy participants underwent conventional/supine and upright CT, and lung attenuation gradients were measured. Lung attenuation gradients in anteroposterior direction were greater in the supine position than in standing position (all p values < 0.0001) in both upper lobes at the level of the aortic arch (right standing/supine, -0.02 ± 0.19/0.53 ± 0.21; left standing/supine, -0.06 ± 0.20/0.51 ± 0.21); in the right middle (standing/supine, -0.26 ± 0.41/0.53 ± 0.39), left upper (standing/supine, -0.35 ± 0.50/0.66 ± 0.54), and lower lobes at the level of the inferior pulmonary vein (right standing/supine, -0.22 ± 0.30/0.65 ± 0.41; left standing/supine, -0.16 ± 0.25/0.73 ± 0.54); and in both lower lobes just above the diaphragm (right standing/supine, -0.13 ± 0.22/0.52 ± 0.32; left standing/supine, -0.30 ± 0.57/0.55 ± 0.37). Craniocaudal gradients were greater in the standing position (right standing/supine, 0.41 ± 0.30/0.00 ± 0.16; left standing/supine, 0.35 ± 0.30/-0.02 ± 0.16, all p values < 0.0001). No moderate to very high correlations were observed between age, sex, height, weight, body index mass, or pulmonary function test results and each lung attenuation gradient. Lung attenuation gradients in anteroposterior direction, which was observed in the supine position, disappeared in the standing position. However, the craniocaudal lung attenuation gradient, which was not present in the supine position, appeared in the standing position.