Lung inflation can cause pulmonary edema in zone I of in situ dog lungs.

We investigated whether increases in lung water can occur due to lung inflation in zone I when alveolar vessels are collapsed. Static left lower lobe alveolar pressure, pulmonary arterial pressure, and pulmonary venous pressure were controlled in living, anesthetized, open-chested dogs. The lobe was inflated with 6% CO2 in air and suspended from a strain gauge, which allowed continual weight recording. The lung was held in zone I conditions. Arterial and venous pressures were equal at either 1 or 5 cmH2O, relative to the base of the 10- to 14-cm-high lobes. Weight changes were measured for 5 min after 5-cmH2O increments of alveolar pressure from 0 or 5 to 30 cmH2O. Lung weight gain due to edema occurred with inflation to alveolar pressures above 10 cmH2O. Greater lung distension resulted in greater rates of weight gain. Weight loss occurred on deflation. The fluid may have leaked from distended extra-alveolar vessels. This mechanism could explain the increased lung water seen with mechanical ventilation and/or positive end-expiratory pressure breathing.