Structure and surface energy of the surfactant layer on the alveolar surface

The surface energy of the alveolar surfactant laver is determined in the sc ore of a modification of the structural model of Larsson et al. [(1999) J D isp Sci Technol 20:1-12], according to which this layer is built up of a li pid monolayer adsorbed at the hypophase/air interface and supported by a ne twork of lipid bilayers immersed into the hypophase, i.e., the alveolar liq uid. Formulae are derived for the dependence of the specific surface energy of the surfactant layer on the distance between the bilayers constituting the layer. It is shown that at equilibrium this energy can have values comp arable with or less than 1 mJ/m(2) needed for normal functioning of the alv eolus during the respiration cycle. The specific surface energy of the surf actant layer with monolayer-bilayer structure can have such low values only if the layer is of optimal thickness and if the specific line energy of th e monolayer-bilayer contact lines is negative and that of the bilayer-bilay er contact lines is positive. It is found that in dynamic regime the change in the specific surface energy of the alveolar surfactant layer with bilay er-monolayer structure is in qualitative agreement with that determined exp erimentally during lung inflation and deflation.