Normal pulmonary geometric changes due to respiration: evaluation with inspiratory and expiratory spiral CT.

Rationale and Objectives: To investigate the pattern of physiological pulmonary geometric changes in the longitudinal direction due to respiration.
Materials and Methods: Spiral CT scans of the lung were obtained in 20 normal subjects at maximal inspiration and expiration, each with a table feed time of 10 mm/sec, collimation of 10 mm, and continuous sections of 5 mm in thickness. Utilizing the pulmonary vessels or bronchi as the reference points and comparing the points of these structures shown on the CT images taken at both respiratory phases, the distance of excursion in the longitudinal direction during respiration was examined. Excursion of pulmonary structures was examined from the upper edge of the manubrium to the top of the diaphragm in three lung zones in the coronal direction.
Results: A significant linear correlation between the distance from the upper edge of the manubrium to the structure and the distance of its excursion was found for all three lung zones (r = 0.84, p < 0.01 for the anterior zone; r = 0.89, p < 0.01 for the middle zone; r = 0.91, p < 0.01 for the posterior zone). The mean value of displacement in posterior zone was significantly greater (p < 0.01) than that in the middle zone, which was significantly greater (p < 0.01) than that in the anterior zone at each level.
Conclusion: We have described the normal longitudinal displacement patterns of the pulmonary structures due to respiration. These findings may be applied to the diagnosis of pulmonary diseases.