Edematous alveolar surface tension in situ in the lung

Edema liquid protein content is thought to inactivate surfactant and increase surface tension, T , in the lung. However, T has not been determined in situ with elevated protein content or edema. Thus, we combined fluorescent confocal imaging of the isolated rat lung with servo‐nulling liquid pressure measurement. To model alveolar edema, we filled an alveolus by microinjection with fluorescently labeled 5% albumin or 4% dextran solution. At constant inflation, we measured alveolar air pressure, P ALV , at the trachea. By servo‐null, we measured alveolar liquid‐phase pressure in an edematous or air‐filled alveolus. Concurrently, to determine interfacial radius, we used an air‐objective to obtain a z‐stack of images of the alveolar air‐liquid interface. By the Laplace relation, we calculated T . With albumin solution, inflation from P ALV of 5 to 15 cmH 2 O increased edematous alveolar T from 3.1±0.5 (n=3, mean±SE) to 13.9±1.7 (n=7) mN/m (p<0.01). At neither P ALV did T differ between edematous and air‐filled (n=3) alveoli. Further, using dextran rather than albumin solution as the model edema liquid, edematous alveolar T was marginally higher, 4.9±0.3 mN/m (n=4, p<0.05), at P ALV of 5 cmH 2 O and not different (n=3) at P ALV of 15 cmH 2 O. Our findings suggest that with liquid‐entry into the alveolus, and even with protein inclusion in the entering liquid, interfacial surface tension remains unchanged. AHA 09SDG2010097