Using Fiji as a simplified tool for assessing alveolar chord length and septal thickness in neonatal pulmonary disease research

Bronchopulmonary Dysplasia (BPD) is a neonatal condition primarily affecting babies born prematurely, who have been exposed to invasive ventilation and/or oxygen supplementation. These therapies predispose the immature developing lungs to inflammation and injury to the alveolar epithelium resulting in loss of the alveolar epithelium and thickening of alveolar septa, the 2 important hallmarks of the pathology of BPD. The expansion and enlargement of the alveolar sacs gives the characteristic feature of alveolar simplification in BPD. To measure this alveolar abnormality, we have modified and developed a custom-made Chord Length Fiji plugin which can easily measure the Chord Length and Septal Thickness on Hematoxylin-Eosin-stained histological lung sections, thus generating an instant morphometry readout for quick interpretation. We validated this plugin in multiple animal experimental models and human neonatal lungs with BPD. We were able to differentiate the morphology under conditions of ventilation or hyperoxia exposure, when compared with untreated controls. We thus conclude that our Chord Length and Septal Thickness plugin can be used in a simplified manner following a less meticulous automated operation. To facilitate global use, we have created a DOI so that any user can access it without any restrictions to complete the morphometric measurements. This plugin will be useful for smaller research laboratories with limited budgets and require no access to complex software.