Abstract
IntroductionBronchopulmonary dysplasia (BPD) is a chronic lung disease associated with premature birth. Hallmark pathologic features of BPD include increased alveolar wall thickness and reduced pulmonary vascular cross sectional area. Measurement of mean linear intercept (MLI) is a tool used to quantify alveolar size, where a higher MLI is suggestive of reduced alveolar surface area. Previous studies have shown an increased MLI in lungs from a BPD rat model in early postnatal life. However, it is unknown if these pathological changes last into adulthood. The purpose of this study was to quantify alveolar size using the mean linear intercept (MLI) technique in lung tissue sections from 7 and 14 day and 1 year old control and BPD rats.MethodsSprague Dawley rat pups were placed in hyperoxic (HYP, 85% O2) or normoxic (NORM, 21% O2) chambers within 12 hours of birth for a total of 14 days, then were moved to room air housing. At 7 and 14 days and 1 year of age, rats (n=2 rats per time point per exposure) were sacrificed and lung tissue sections were placed on slides and stained with hematoxylin and eosin (H&E). 9 images from each lung cross section were collected and analyzed. Alveolar air space was determined using the MLI method where horizontal grids were placed on images and intersections with the tissue were counted. For each image, MLI was calculated using the following equation: Lm = number of intersections/(grid length (um) × number of lines). The 9 values were averaged, giving an MLI score for each animal. Two‐way ANOVA was used to determine the main effect for age (7, 14, 360 d), condition (NORM vs HYP), and the interaction between age and condition. Statistical significance was defined as p < 0.05.ResultsHYP rats have a significantly greater MLI (p=0.01) compared to NORM rats at all time points. At 7 days, HYP rats had a 43% increase in MLI compared to NORM. At 14 days, HYP rats had an 18.5% increase. At one year, HYP rats had a 47% increase.ConclusionMean linear intercept is significantly increased a rat model of BPD, which persists well into adulthood. Enlargement of the distal airspaces likely plays a role in the diminished gas exchange observed in BPD.Support or Funding InformationNHLBI, R01 HL115061‐03, Suppl (Eldridge) & NHLBI, R01 HL115061 (Eldridge)
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