Ventilatory capacity in CLAD is driven by dysfunctional airway structure.

Background: Chronic lung allograft dysfunction (CLAD) encompasses three main phenotypes: bronchiolitis obliterans syndrome (BOS), restrictive allograft syndrome (RAS) and a Mixed phenotype combining both pathologies. How the airway structure in its entirety is affected in these phenotypes is still poorly understood.
Methods: A detailed analysis of airway morphometry was applied to gain insights on the effects of airway remodelling on the distribution of alveolar ventilation in end-stage CLAD. Ex vivo whole lung μCT and tissue-core μCT scanning of six control, six BOS, three RAS and three Mixed explant lung grafts (9 male, 9 female, 2014-2021, Leuven, Belgium) were used for digital airway reconstruction and calculation of airway dimensions in relation to luminal obstructions.
Findings: BOS and Mixed explants demonstrated airway obstructions of proximal bronchioles (starting at generation five), while RAS explants particularly had airway obstructions in the most distal bronchioles (generation >12). In BOS and Mixed explants 76% and 84% of bronchioles were obstructed, respectively, while this was 22% in RAS. Bronchiolar obstructions were mainly caused by lymphocytic inflammation of the airway wall or fibrotic remodelling, i.e. constrictive bronchiolitis. Proximal bronchiolectasis and imbalance in distal lung ventilation were present in all CLAD phenotypes and explain poor lung function and deterioration of specific lung function parameters.
Interpretation: Alterations in the structure of conducting bronchioles revealed CLAD to affect alveolar ventilatory distribution in a regional fashion. The significance of various obstructions, particularly those associated with mucus, is highlighted.
Funding: This research was funded with the National research fund Flanders (G060322N), received by R.V.
Competing Interests: Declaration of interests JK and VG and MV are junior research fellows of the Research Foundation Flanders (FWO; 1198920N and 1102020N and 1SE433N). MV received compensation from Sanofi for attending the ERS 2023 congress. GPLA is a supported by an European Respirology Society Clinical Fellowship Grant. SB is supported by the Paul Corris International Clinical Research Training Scholarship. LJDS (De Sadeleer) is supported by the European Union's Horizon Europe research and innovation programme as a Marie Sklodowska-Curie actions postdoctoral fellowship (grant agreement No. 101066289).
(Copyright © 2024 The Authors. Published by Elsevier B.V. All rights reserved.)