Alveolar liquid pressures in nonedematous and kerosene-washed rabbit lung by micropuncture

We studied the relationship between alveolar interfacial pressure and lung volume in kerosene-filled lungs, nonedematous air-filled lungs on lung deflation and inflation, and air-filled lungs after washing with kerosene or the Dow Corning oil, 0.65 cs dimethyl siloxane (DC200). We used the micropipet-servonulling technique to measure alveolar liquid pressure (Pliq) in the alveolar liquid layer of isolated rabbit lungs at different airway pressures (Palv). It was not possible to measure pressure in kerosene or in DC200 by micropuncture because of its low electrical conductivity. We used the Laplace law for a spherical membrane to estimate alveolar surface tension (T). In the kerosene-filled lung, the pressure drop (delta P = Pliq - Palv) across the alveolar surfactant-kerosene interface was 1.1 cm H2O at TLC and decreased to 0.5 cm H2O at 71% TLC. These values corresponded to T values of 2.2 and 0.9 dyne/cm at TLC and 71% TLC, which were in agreement with in vitro measurements using the captive bubble technique. In the air-filled lung on inflation, delta P values were 12.7 and 15.7 cm H2O at 48% and 76% TLC. Corresponding T values were 14 and 21 dyne/cm. Thus, alveolar surface tension on lung inflation is surface area dependent. In the kerosene-washed and DC200-washed lungs, delta P values were 16 and 14.5 cm H2O at TLC and decreased to 9 and 8 cm H2O at 50-56% TLC. These values indicated a reduction of 40-60% in alveolar surface tension with lung deflation from TLC to 50% TLC. The results indicate that alveolar surface tension in both kerosene-filled and kerosene-washed air-filled lungs is surface area dependent. This is due to a surfactant-kerosene interface in the kerosene-filled lung and a surfactant-kerosene-air interface in the kerosene-washed lung.