Properties of four lung surfactants and their mixtures under physiological conditions

Surface properties of four of the most prevalent surfactants found in the lung have been studied on the Langmuir trough under simultaneously simulated physiological conditions. Surfactants studied are dipalmitoyl lecithin (DPL), L-alpha-dipalmitoyl phosphatidyl D,L-glycerol (DPPG), dipalmitoyl phosphatidyl ethanolamine (DPPE) and sphingomyelin and various mixtures of these. Studies using both the Wilhelmy and Ring methods showed that only sphingomyelin displayed any appreciable hysteresis between surface tension and surface area. All surfactants and their various mixtures reached similar minimal surface tension values of about 24-26 dyne/cm for compression to 75% of initial area and they all showed more than twice the change in surface tension with area needed to impart alveolar stability. These surfactants and their mixtures (except sphingomyelin) displayed appreciable contact angles, reaching 53 degrees for DPPE and 55 degrees C for a 1 : 1 mixture of DPL and DPPG. These mild anti-wetting properties are discussed in relation to their implications to gas transfer and fluid distribution at the alveolar wall.