Ultrastructural analysis of sheep lungs after increased intracranial pressure and development of pulmonary edema.

The effect of neurogenic pulmonary edema on the ultrastructure of the gas exchanging region of the mammalian lung is unclear. The present study reports a morphometric and ultrastructural analysis of the alveolar-capillary septa of the lungs of anesthetized sheep subjected to elevated intracranial pressure during hydrostatic recruitment of pulmonary microvascular surface area. In experimental animals septal interstitial thickness was increased and evidence of interstitial edema was presented. Compared to control animals, the density of endothelial plasmalemmal vesicles was nearly doubled and was associated with fluid distention of the septal interstitium. In no instance were endothelial blebs or other discontinuities characteristic of increased permeability edema observed in septal exchange vessels. The data support previous observations which suggested that pulmonary edema caused by elevated intracranial pressure is pressure rather than permeability dependent.