Location-specific pathology analysis of the monopodial pulmonary vasculature in a rabbit model of bronchopulmonary dysplasia-A pilot study.

The mammalian pulmonary vasculature consists of functionally and morphologically heterogeneous compartments. When comparing sets of lungs, for example, in disease models or therapeutic interventions, local changes may be masked by the overall heterogeneity of the organ structure. Therefore, alterations taking place only in a sub-compartment may not be detectable by global analysis. In the monopodial lung, the characterization of distinct vessel groups is difficult, due to the asymmetrical branching pattern. In this pilot study, a previously established method to classify segments of the monopodial pulmonary arterial tree into homogeneous groups was employed. To test its suitability for experimental settings, the method was applied to a hyperoxia (HYX, ≥95% oxygen) rabbit model of bronchopulmonary dysplasia and a normoxic control group (NOX, 21% oxygen). The method allowed the identification of morphological differences between the HYX and the NOX groups. Globally visible differences in lumen diameter were pinpointed to specific lung regions. Furthermore, local changes of wall dimension and cell layers in single compartments, that would not have been identifiable in an unfocused analysis of the whole dataset, were found. In conclusion, the described method achieves a higher precision in morphological studies of lung disease models, compared to a common, global analysis approach.

Combination of µCT and light microscopy for generation-specific stereological analysis of pulmonary arterial branches: a proof-of-concept study.

Various lung diseases, including pulmonary hypertension, chronic obstructive pulmonary disease or bronchopulmonary dysplasia, are associated with structural and architectural alterations of the pulmonary vasculature. The light microscopic (LM) analysis of the blood vessels is limited by the fact that it is impossible to identify which generation of the arterial tree an arterial profile within a LM microscopic section belongs to. Therefore, we established a workflow that allows for the generation-specific quantitative (stereological) analysis of pulmonary blood vessels. A whole left rabbit lung was fixed by vascular perfusion, embedded in glycol methacrylate and imaged by micro-computed tomography (µCT). The lung was then exhaustively sectioned and 20 consecutive sections were collected every 100 µm to obtain a systematic uniform random sample of the whole lung. The digital processing involved segmentation of the arterial tree, generation analysis, registration of LM sections with the µCT data as well as registration of the segmentation and the LM images. The present study demonstrates that it is feasible to identify arterial profiles according to their generation based on a generation-specific color code. Stereological analysis for the first three arterial generations of the monopodial branching of the vasculature included volume fraction, total volume, lumen-to-wall ratio and wall thickness for each arterial generation. In conclusion, the correlative image analysis of µCT and LM-based datasets is an innovative method to assess the pulmonary vasculature quantitatively.

A Systematic Review of the Influence of Continuous Positive Airway Pressure on Fetal and Newborn Animal Models: Suggestions to Improve Neonatal Respiratory Care.

INTRODUCTION: Prematurely born infants regularly develop respiratory distress syndrome and require assisted ventilation. Ventilation may injure the premature lung and increase the risk of bronchopulmonary dysplasia. Continuous positive airway pressure (CPAP), a form of noninvasive ventilation, is commonly used in modern neonatology. Limited clinical data are available on the acute and long-term effect of neonatal exposure to CPAP on the lung. Given the restricted clinical data, newborn animal models have been used to study the influence of CPAP on lung structure and function. The findings of animal studies can guide neonatal care and improve the use of CPAP. METHODS: A systematic review of electronic databases (Medline, Embase, and Cinahl) was performed using the medical subject heading terms, "CPAP" or "continuous positive airway pressure" and "animals" and "newborn." Abstracts were screened for inclusion using predetermined eligibility criteria. RESULTS: In total, 235 abstracts were identified and screened for inclusion. Of these, 21 papers were included. Large (N = 18) and small (N = 3) animal models investigated the effects of CPAP. Pulmonary outcomes included gas exchange, lung structure and function, surfactant metabolism, lung inflammation and injury, and the effect of intrapulmonary therapy. Compared to mechanical ventilation, CPAP improves lung function, evokes less lung injury, and does not disrupt alveolar development. Surfactant administration combined with CPAP further improves respiratory outcomes. Of concern are findings that CPAP may increase airway reactivity. DISCUSSION/CONCLUSION: CPAP offers numerous advantages over mechanical ventilation for the immature lung. The combination of CPAP and exogenous surfactant administration offers further pulmonary benefit.

Intermittent CPAP limits hyperoxia-induced lung damage in a rabbit model of bronchopulmonary dysplasia.

A significant proportion of preterm infants develop bronchopulmonary dysplasia (BPD) leading to poor lifelong respiratory health. Limited treatment options exist with continuous positive airway pressure (CPAP) ventilation being one of the few associated with diminished BPD. However, little is known about the effect of the distending pressure of CPAP on the developing lung exposed to hyperoxia. We aimed to identify the functional and structural effects of CPAP in a preterm hyperoxia rabbit model of BPD. Premature rabbit pups were randomized to normoxia, hyperoxia (≥95% O2), or hyperoxia plus 4 h daily CPAP [fraction of inspired oxygen (FiO2) 0.95, 5 cmH2O]. On day 7 postdelivery we performed invasive pressure-volume- and forced oscillation-based pulmonary function tests, before lung harvest for histological evaluation. Alveolar and vascular morphology, airway smooth muscle content, respiratory epithelium height, extracellular matrix components, and inflammatory cytokine expression were quantified. Hyperoxia-reared pups had restrictive lungs: alveolar walls were thickened, with the lung parenchymal tissue, collagen content, and airway smooth muscle content increased. In addition, peripheral pulmonary artery wall thickness was increased. CPAP increased alveolar recruitment and limited the structural effect of hyperoxia on the respiratory epithelium and pulmonary arteries. Additionally, CPAP improved lung function, mitigating hyperoxia-associated changes to respiratory system resistance, tissue damping, and tissue elastance. Hyperoxia disrupted functional and structural lung development. Daily intermittent CPAP limited hyperoxia-associated decreased lung function and attenuated structural changes to pulmonary arteries and respiratory epithelium while having no structural alveolar consequences. The mechanism by which CPAP has these beneficial effects needs further investigation.