Direct determination of surface tension in the lung.

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Abstract
The spreading behavior of small drops of several fluorocarbon fluids and silicone oil on air-liquid interfaces was used to measure the surface tension of lungs in situ. The test fluids were calibrated in a surface balance at 37.degree. C on monolayers of dipalmitoylphosphatidylcholine. At particular surface tensions characteristic of each fluid used, an increase in the tension of 1 mN/m or less caused the droplets to spread reversibly from a sphere to a lens shape. Using micropipettes, such droplets were placed on the alveolar surfaces of excised rat lungs held at functional residual capacity and 37.degree. C and it was found that the surface tension remained below 9 mN/m for at least 30 min. The surface tension-volume relationship was linear for tensions ranging from 9 to 20 mN/m.