Development and regression of pulmonary arterial lesions after experimental air embolism. A light and electronmicroscopic study.

Repeated systemic venous air embolism produces pulmonary vascular lesions, the nature of which is still a subject of controversy. We investigated the pulmonary arterial lesions produced by repeated air embolism in rabbits, both at light and electron microscopic level. We found that they form a remarkable histopathological entity, consisting of initial pronounced vasoconstriction, combined with severe intimal inflammatory changes. Within 4 days after the last injection of air, peculiar sheet-like structures consisting of oedematous tissue and lined by endothelium, projected into the lumen. These structures probably resulted from the shearing stress of the blood, streaming over the severely oedematous intima. They subsequently became thinner and disappeared after two weeks. Various types of blood-borne and mesenchymal cells were present in the thickened intima and within the sheets. The origin of the latter cells remained undecided. They may originate from medial smooth muscle cells penetrating the internal elastic lamina as well as by transition from blood-borne cells into mesenchymal cells, or both.