Nebulisation of monodisperse latex sphere suspensions in air-jet and ultrasonic nebulisers

Therapeutic steroid suspensions are frequently administered via nebulisation to neonates and young children. We sought to investigate how the size and concentration of model-suspended particles (latex spheres) would influence the physical characteristics of the nebulised aerosol. Suspensions of monodispersed latex spheres [from 0.605 to 11.90 mu m: diluted 0.1 to 0.01% (w/v)] were nebulised in three air-jet nebulisers and one ultrasonic nebuliser. Secondary aerosol characteristics were measured with a Malvern 2600C laser diffraction sizer. The residual volumes and percentage outputs of suspension and latex spheres were determined by weight measurements and Coulter Counter analysis. The choice of nebuliser markedly influenced the size, polydispersity and output of the resultant aerosol. No specific correlation existed between the size and/or concentration of the original latex spheres and the size distribution of the nebulised droplets. There was a higher output of smaller spheres, with little or no release of the spheres whose size exceeded the typical mass median diameter of the aerosols. The latex spheres were generally concentrated in the residual fluid due to solvent evaporation, blockage of nebuliser orifice by spheres and/or the refluxing action of the suspension. The ultrasonic nebuliser was less efficient than the jet devices; it degraded the larger spheres and was unable to atomise the 1.16 mu m sphere suspensions.