Quantitative CT-based structural alterations of segmental airways in cement dust-exposed subjects

Abstract

Background: Dust exposure has been reported as a risk factor of pulmonary disease, leading to alterations of segmental airways and parenchymal lungs. This study aims to investigate alterations of quantitative computed tomography (QCT)-based airway structural and functional metrics due to cement-dust exposure.

Methods: To reduce confounding factors, subjects with normal spirometry without fibrosis, asthma and pneumonia histories were only selected, and a propensity score matching was applied to match age, sex, height, smoking status, and pack-years. Thus, from a larger data set (N = 609), only 41 cement dust-exposed subjects were compared with 164 non-cement dust-exposed subjects. QCT imaging metrics of airway hydraulic diameter (D_h), wall thickness (WT), and bifurcation angle (θ) were extracted at total lung capacity (TLC) and functional residual capacity (FRC), along with their deformation ratios between TLC and FRC.

Results: In TLC scan, dust-exposed subjects showed a decrease of D_h (airway narrowing) especially at lower-lobes (p < 0.05), an increase of WT (wall thickening) at all segmental airways (p < 0.05), and an alteration of θ at most of the central airways (p < 0.001) compared with non-dust-exposed subjects. Furthermore, dust-exposed subjects had smaller deformation ratios of WT at the segmental airways (p < 0.05) and θ at the right main bronchi and left main bronchi (p < 0.01), indicating airway stiffness.

Conclusions: Dust-exposed subjects with normal spirometry demonstrated airway narrowing at lower-lobes, wall thickening at all segmental airways, a different bifurcation angle at central airways, and a loss of airway wall elasticity at lower-lobes. The airway structural alterations may indicate different airway pathophysiology due to cement dusts.

Keywords: Airway narrowing; Bifurcation angle; Percent emphysema; Stiffness of airway structure; Wall thickening.

Fig. 1

Flow chart of subject selection for dust-exposed subjects and non-dust-exposed subjects. FEV₁, forced expiratory volume in 1 s; FVC, forced vital capacity

Fig. 2

Labels of 26 segmental airways and 5 subgroups of lobes. BronInt, bronchus intermedius; LMB, left main bronchus; RMB, right main bronchus; sLLL, subgrouped left lower lobe including branches of LB6 and LB8 to LB10; sLUL, subgrouped left upper lobe including branches of LB1 to LB5; sRLL, subgrouped right lower lobe including branches of RB6 to RB10; sRML, subgrouped right middle lobe including branches of RB4 and RB5; sRUL, subgrouped right upper lobe including branches of RB1 to RB3; TriLUL, trifurcation of left upper lobe; TriRUL, trifurcation of right upper lobe

Fig. 3

Comparison of luminal hydraulic diameter (D_h) at TLC (a, b, and c) and FRC scans (d, e, and f) between non-dust-exposed subjects and dust-exposed subjects. Values are presented as mean (CI); *P < 0.05; **P < 0.01; ***P < 0.001. Generation zero is started from trachea. BronInt, bronchus intermedius; D_h, hydraulic diameter; FRC, functional residual capacity; LMB, left main bronchus; RMB, right main bronchus; sLLL, subgrouped left lower lobe; sLUL, subgrouped left upper lobe; sRLL, subgrouped right lower lobe; sRML, subgrouped right middle lobe; sRUL, subgrouped right upper lobe; TLC, Total lung capacity; TriLUL, trifurcation of left upper lobe; TriRUL, trifurcation of right upper lobe

Fig. 4

Comparison of wall thickness (WT) at TLC (a, b, and c) and FRC scans (d, e, and f) between non-dust-exposed subjects and dust-exposed subjects. Values are presented as mean (CI); *P < 0.05; **P < 0.01; ***P < 0.001. Generation zero is started from trachea. BronInt, bronchus intermedius; FRC, functional residual capacity; LMB, left main bronchus; RMB, right main bronchus; sLLL, subgrouped left lower lobe; sLUL, subgrouped left upper lobe; sRLL, subgrouped right lower lobe; sRML, subgrouped right middle lobe; sRUL, subgrouped right upper lobe; TLC, total lung capacity; TriLUL, trifurcation of left upper lobe; TriRUL, trifurcation of right upper lobe

Fig. 5

Comparison of airway bifurcation angle (θ) at TLC (a) and FRC (b) scans between non-dust-exposed subjects and dust-exposed subjects. Values are presented as mean (CI); *P < 0.05; **P < 0.01; ***P < 0.001. BronInt, bronchus intermedius; FRC, functional residual capacity; LMB, left main bronchus; RMB, right main bronchus; TLC, total lung capacity; TriLUL, trifurcation of left upper lobe; TriRUL, trifurcation of right upper lobe

Fig. 6

Comparison of deformation ratio of wall thickness (ε^WT) between non-dust-exposed subjects and dust-exposed subjects. Values are presented as mean (CI); *P < 0.05; **P < 0.01; ***P < 0.001. Generation zero is started from trachea. BronInt, bronchus intermedius; FRC, functional residual capacity; LMB, left main bronchus; RMB, right main bronchus; sLLL, subgrouped left lower lobe; sLUL, subgrouped left upper lobe; sRLL, subgrouped right lower lobe; sRML, subgrouped right middle lobe; sRUL, subgrouped right upper lobe; TLC, total lung capacity; TriLUL, trifurcation of left upper lobe; TriRUL, trifurcation of right upper lobe

Fig. 7

Bifurcation angle of airway in a non-dust-exposed subject at TLC (a) and FRC (b) scans and a dust-exposed subject at TLC (c) and FRC (d) scans. FRC, functional residual capacity; LMB, left main bronchus; RMB, right main bronchus; TLC, total lung capacity

Fig. 8

Parenchymal features of Emph% and fSAD% in a non-dust-exposed subject (a) and a dust-exposed subject (b)