LEAKAGE OF MACROMOLECULES IN VENTILATED AND UNVENTILATED SEGMENTS OF PRETERM LAMB LUNGS

The movement of macromolecules into and out of unventilated lung segments was evaluated in prematurely delivered and ventilated lambs. Seven lambs at 130 days gestational age had a bronchial balloon placed at birth before the first breath to obstruct the left lower lobe. Surfactant and I-131-albumin were instilled into the left lower lobe while surfactant and I-125-albumin were instilled into the remaining lung, and 70,000 molecular weight ]H-3[dextran was given into the vascular space at birth. Twenty-five percent of the lung by weight was not ventilated, and 24 % of the total leak of dextran from the vascular space was recovered in the unventilated lungs at 3 h. An epithelial leak of protein from the two lung regions was documented by the loss of 11.4 and 18.4 % of the labeled albumins in the nonventilated and ventilated lung regions, the appearance of 4.9 and 7.5 % of the airway-instilled albumin in the vascular space from the nonventilated and ventilated lung regions, and the recovery of the labeled albumins in the carcasses of the lambs. The bidirectional flux of macromolecules was larger in the ventilated than in the nonventilated lung regions, indicating that ventilation can increase the leak of protein in the preterm lung. The lung areas that were never exposed to ventilation or oxygen also demonstrated a large bidirectional flux of macromolecules, a finding not present in the fetus, full-term newborn, or adult. These findings indicate that ventilation is not solely responsible for the increased protein leak found in preterm lungs. We speculate that a mechanism independent of ventilation is acting postnatally on the preterm lung that leads to large flux of macromolecules across the alveolar epithelium. This background leak is a function of immaturity and may be compounded by excessive ventilation.