Reactive Changes in Pulmonary Parenchyma After Bilobectomy: A Scanning Electron Microscopic Investigation

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Abstract
Morphology of the adaptive response of the pulmonary parenchyma after resection of lung tissue is described. Rats aged 23 days were subjected to bilobectomy of the right upper and middle lobes, representing 25% of the total lung volume. On postoperative days 1, 4, 6, 9, 12, 18 and 30, the lungs were fixed by standardized intratracheal instillation of fixative, their volume determined by water displacement and pieces of the left lung prepared for scanning electron microscopy (SEM). Age-matched normal and sham-operated animals served as controls. Lung volumes of operated rats rapidly matched control values. In SEM the volume gain appeared to be achieved by a widening of the airspaces affecting primarily the alveolar ducts on postoperative day 1 and shifting later to the alveolar level (day 4). On days 4 and 6, the interalveolar septa were slightly thickened, presumably due to a proliferative response in the tissue, which is well documented in the literature. From day 9 onward, morphology of bilobectomized lungs did not differ from normal. In no instance could we detect clues for the formation of new alveoli. Several possible explanations for this structural recovery of the pulmonary parenchyma are discussed. Among these, a model is presented illustrating how the parenchymal morphology can be apparently normalized by the tissue proliferation, which renders the original widening of the airspaces unobtrusive on random sections through the respiratory tissue.