Airway and lung parenchyma morphology during the respiratory cycle

Describe the morphological changes that take place in the lung parenchyma and in the airways during the respiratory cycle with a view to establishing a relationship between them.

Adult Wistar rats.

The lungs were fixed at seven different points in the respiratory cycle: Inflation, 10 and 20 cm. transpulmonary pressure, total lung capacity. Deflation, 20, 15, 10 and 0 cm transpulmonary pressure.

The lungs were processed for morphometric study and bronchial and parenchymal variables, such as lung volume, number of alveoli, anatomic dead space, bronchial lumen surface and bronchial wall surface were quantified. The results were compared by analysis of variance (ANOVA) or the Kruskal-Wallis and Mann-Whitney's U tests.

The lung volume, the number of alveoli and the anatomic dead space increased with the increase of the transpulmonary pressure and decreased with the decrease of it, the obtained values in deflation being higher than those in inflation (p<0.05). The bronchial lumen and the bronchial wall surfaces generally showed higher values in inflation than in deflation (p<0.05).

The anatomic dead space was altered as a consequence of the variations in airway diameter and length. Lung parenchyma tension may have been of influence in the variations of the bronchial wall.