Ultrasonic and jet aerosolization of phospholipids and the effects on surface activity

Surface active aerosols were produced from aqueous dispersions of mixed lipids (CLL), extracted from bovine lung lavage. Particle size distributions were measured as a function of humidity for two types of aerosol generators: ultrasonic and jet. Lipid dispersions before aerosolization were prepared by sonication in an ice bath and by mechanical vortexing. Over a range of high humidity greater than 60-70%, ultrasonic nebulization gave CLL aerosols with mass median aerodynamic diameters (MMAD) of 1.4 +/- 0.1 micron, compatible with predicted alveolar deposition fractions of 0.2-0.3 according to current deposition models. For humidities of 30-95%, jet nebulization gave MMAD values of 0.4-0.5 micron, which have lower predicted alveolar deposition. The surface pressure-time (pi - t) adsorption characteristics at 35 +/- 2 degrees C of CLL dispersions prepared initially by vortexing or sonication were not significantly affected by ultrasonic nebulization over a 1-2 h time period. In addition, the dynamic surface tension lowering of both kinds of CLL dispersion was not affected by ultrasonic nebulization (minimum surface tension less than 1 dyne/cm at 37 degrees C and 100% humidity). Current interest in the treatment of the respiratory distress syndrome (RDS) with exogenous surfactant replacement has focused largely on the delivery of surfactant replacement has focused largely on h delivery of surfactants to infants by tracheal instillation at birth. However, the ability to form multi-component surfactant aerosols with appreciable alveolar deposition fractions and high surface activity may help to expand the utility of replacement therapy to patients with aerated lungs.