Effects of 100% O2 breathing on permeability of alveolar epithelium to solute.

We measured the effects of 100% O2 exposure at 1 atm for 48 (n = 5) and 63 h (n = 6) on the solute permeability of the alveolar epithelium of rabbits. We instilled 10-15 ml of saline containing trace amounts of 131I-albumin (r approximately 35 A), 125I-cytochrome c (r approximately 17 A), and [57Co]cyanocobalamin (r approximately 6.5 A) into an atelectatic segment of the right lower lobe. Egress of these tracers was determined from their change in concentration in the alveolar saline and their detection in arterial blood. All tracers left the alveolar space and appeared in the arterial blood on the 63-h O2 group, cytochrome c and cyanocobalamin in the 48-h O2 group, and only cyanocobalamin in the control (air breathing). The O2-exposed animals had PaO2 values higher than 500 Torr, normal PaCO2 and pH, and wet-to-dry lung weight ratios not different from control. We concluded that increasing the length of O2 exposure increases the solute permeability of the alveolar epithelium and this precedes the appearance of pulmonary edema.