Rapidly alternating curvature ("oil canning") as a mechanism preventing alveolar edema

This study has been designed to investigate the concept that the passage of red blood cells (clearly seen "bulging" into the air space in all scanning electron micrographs of the alveolar surface) can produce a net force tending to return any excess fluid to the interstitium. Measurements of surface tension over the time frame and probable surface area excursion incurred by a passing red blood cell show an appreciably higher value corresponding to the expanding surface, which is convex with respect to air, than when it is compressing and concave. The mean difference in surface tension of about 16 dyn/cm (mN/m) translates into a net driving force of approximately 6 mmHg induced by this rapidly alternating microcurvature reflecting the highly dynamic state of the living alveolar wall. The significance of the microcurvature of the alveolar surface is emphasized in relation to surfactant function.