C73-01 Quantitative CT Lung Structure-function Impairment in Normal-appearing Elderly Individuals With Absent Right Medial-basal Bronchus

Rationale Anatomical variants in airway branching, such as the presence of an accessory sub-superior branch (Acc) and absence of the right medial-basal bronchus (Abs), represent congenital variations that are associated with chronic obstructive pulmonary disease (COPD) and may influence airway and lung impairment (PMID 29339516). This study aimed to explore distinct lung structural and functional impairment in elderly people with no known prior lung disease. Methods Inspiratory (total lung capacity) and expiratory (residual volume) computed tomography (CT) images, demographic, and spirometry (baseline and 1-year follow-up) data were collected from 66 elderly healthy individuals with normal lung function (68±10 years old; FEV1%=117±22; FVC%=109±16) in Seoul National University Hospital (Seoul, Korea) between 2018 and 2022. VIDA Vision 2.2 (Coralville, IA), in-house software, and visual inspection were used for quantitative CT (qCT) analysis and airway variant identification. Demographics, spirometry, and qCT features were compared between four airway variant subgroups (Acc, Abs, Both, Neither) using Kruskal-Wallis and Dunn’s post hoc tests. Discriminative qCT features were further evaluated by SHAP (SHapley Additive exPlanations) analysis via machine learning classification. Results Individuals in the Acc/Abs/Both/Neither groups were 9%/16%/5%/70%, respectively. The Abs group had the highest air trapping (AirT%=33.4%, p = 0.009), inspiratory low attenuation area below -950 HU (LAAIN%=20.7%, p = 0.006), and functional small airways disease (fSAD%=18.4%, p = 0.034), and the lowest lung deformation index (Jacobian=1.58, p = 0.022) and relative displacement (s*=0.181, p = 0.028). Demographics, spirometry (baseline and 1-year change), and airway metrics were not significantly different. Mucus plugs were observed in 3 Neither and 1 Abs group members. SHAP analysis found LAAIN% and AirT% as the most and second-most discriminative features, which is supported by bi-serial correlation coefficient of 0.39 (p = 0.001) and 0.37 (p = 0.003), respectively. Conclusion Among elderly individuals with normal lung function on spirometry, individuals with absent right medial-basal bronchus showed worse qCT functional features of enlarged air space (hyperinflated or emphysematous) and air trapping resulting in reduced lung deformation. Airway variant identified by inspiratory CT may serve as an imaging biomarker for subclinical regional lung impairment leading to the development of COPD. This abstract is funded by: Korea Environmental Industry & Technology Institute (KEITI) grant 2018001360001, National Research Foundation of Korea (NRF) grant RS-2025-00521675, and Seoul National University Mid-Career Bridging Program grant 800-20220619