Comparison of inspiratory and expiratory airway volumes and luminal areas among standing, sitting, and supine positions using upright and conventional CT

Abstract

Upright computed tomography (CT) provides physiologically relevant images of daily life postures (sitting and standing). The volume of the human airway in sitting or standing positions remains unclear, and no clinical study to date has compared the inspiratory and expiratory airway volumes and luminal areas among standing, sitting, and supine positions. In this prospective study, 100 asymptomatic volunteers underwent both upright (sitting and standing positions) and conventional (supine position) CT during inspiration and expiration breath-holds and the pulmonary function test (PFT) within 2 h of CT. We compared the inspiratory/expiratory airway volumes and luminal areas on CT among the three positions and evaluated the correlation between airway volumes in each position on CT and PFT measurements. The inspiratory and expiratory airway volumes were significantly higher in the sitting and standing positions than in the supine position (inspiratory, 4.6% and 2.5% increase, respectively; expiratory, 14.9% and 13.4% increase, respectively; all P < 0.001). The inspiratory and expiratory luminal areas of the trachea, bilateral main bronchi, and average third-generation airway were significantly higher in the sitting and standing positions than in the supine position (inspiratory, 4.2‒10.3% increases, all P < 0.001; expiratory, 6.4‒12.8% increases, all P < 0.0001). These results could provide important clues regarding the pathogenesis of orthopnea. Spearman’s correlation coefficients between the inspiratory airway volume on CT and forced vital capacity and forced expiratory volume in 1 s on PFT were numerically higher in the standing position than in the supine position (0.673 vs. 0.659 and 0.669 vs. 0.643, respectively); however, no statistically significant differences were found. Thus, the airway volumes on upright and conventional supine CT were moderately correlated with the PFT measurements.

Upright CT-based evaluation of the effects of posture on skull-base reconstruction after endoscopic endonasal surgery

“…The patients underwent an upright CT scan (prototype TSX-401R; Canon Medical Systems, Otawara, Japan) in the sitting position and a conventional supine CT scan (Aquilion ONE; Canon Medical Systems) in the supine position in a prospectively randomized order. The upright CT scan was performed with 320 detector rows, and its performance was comparable to that of a conventional supine CT scan, as described previously [3,[11][12][13]. Both CT scans were performed under the same conditions at 120 kVp, with a noise index of 4 for a 5-mm slice thickness.…”