Vascular Changes in Chronic Experimental Atelectasis.

Microscopic pathology of massive atelectasis in man has received little consideration due to its associated low mortality. Reports on this subject have usually been made on autopsies where death was due to some other cause. Bergamini and Shepard 1 reported 2 cases of bilateral massive atelectasis causing sudden death. Microscopic sections of the collapsed lungs revealed cloudy swelling and indistinct outline of the cells; with a dilatation of the capillaries, arterioles and venules which were filled with blood, presenting in parts an angiomatous appearance. From experimental studies it has generally been contended that there appears to be an increased vascularity of the atelectatic tissue; that the capillaries become dilated and engorged with blood simulating a passive congestion of the lung lobe.

Recently we have studied microscopic sections of experimental atelectasis at various stages of duration. Massive atelectasis was produced in dogs by stenosis of the bronchi with a solution of silver nitrate. 2 The dogs were sacrificed at irregular intervals ranging from a few days to several months.

Atelectasis of only a few days'duration revealed complete collapse of the alveolar spaces and smaller bronchioles with some swelling of the septal cells whose outlines were indistinct. There was an apparent increase in the vascularity of the tissue due to the capillary spaces being brought much closer together. These vascular channels appeared to be engorged with blood, giving it the appearance of a passive congestion. Anthracosis was present, scattered pigment appearing throughout the tissue.

By the end of 4 months the alveolar walls were much less closely packed together and the intervening greatly dilated blood spaces more clearly outlined at this time. The blood spaces gradually become larger so that at the end of g and I I months, they were found enormously dilated; some being 2 or 3 times as large as an ordinary alveolus.