Aerosol Particle Size Determinations with the R.C.I. Nebulizer Using Holographic Microscopy

Studies of the R.C.I. Nebulizer were conducted to determine the particle size distributions under variable operating conditions optional to the user, namely heating the water prior to nebulization and entrainment of room air into the aerosol-oxygen mixture when 100 per cent oxygen is undesirable for patient treatment. Holographic microscopic determinations of particle size distribution by count were made while the nebulizer was operated under the four possible combinations of conditions presented by the two variables. From these data were calculated the count median diameter, mass median diameter, geometric standard deviations, and the percentage of respirable particles (less than 5 microns diameter) by mass, the latter parameter being most indicative of aerosol efficacy for inhalation therapy. Results of the studies showed that when the nebulizer was operated in the ‘normal’ mode, that is, with no heater and with 100 per cent oxygen, 50 per cent by mass of the aerosol was respirable. As the result of either preheating the water or entraining room air, the respirable fraction increased to about 80 per cent. When preheating and air entrainment were employed simultaneously, 40 per cent respirable mass was observed.