Direct determination of surface tension in the lung.

TLDR

The authors measured lung surface tension in situ by observing the reversible spreading of calibrated fluorocarbon and silicone oil droplets on alveolar surfaces of excised rat lungs at 37 °C and functional residual capacity. Surface tension stayed below 9 mN/m for at least 30 min, and the tension–volume relationship was linear between 9 and 20 mN/m.

Abstract

We have used the spreading behavior of small drops of several fluorocarbon fluids and silicone oil on air-liquid interfaces to measure the surface tension of lungs in situ. The test fluids were calibrated in a surface balance at 37 degrees 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 we placed such droplets on the alveolar surfaces of excised rat lungs held at functional residual capacity and 37 degrees and 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.