FINE-PARTICLE FRACTION AS A MEASURE OF MASS DEPOSITING IN THE LUNG DURING INHALATION OF NEARLY ISOTONIC NEBULIZED AEROSOLS

The amount of aerosol inhaled in different fine particle definitions i s compared to the amount of aerosol depositing in the lung and alveola r regions for nearly isotonic nebulized aerosols. These comparisons ar e made using a two-way coupled hygroscopic deposition model with exper imental data obtained for over 200 different nebulizers from 19 differ ent nebulizer models nebulizing salbumatol sulphate (1 mg ml(-1) in is otonic saline). Mass depositing in the lungs and mass inhaled in parti cles with diameters 1-6 mu m are statistically different (p < 0.05). R esults are also presented for log-normally distributed aerosols as a f unction of mass median aerodynamic diameter (MMAD) ranging from 1.0 to 9.0 mu m and geometric standard deviations (GSDs) from 1.0-2.5. Fine particle fraction definitions of 0-5, 1-5, 0-6, 1-7 and 1-10 mu m are considered. For the polydisperse aerosols considered, each inhaled fin e particle mass is equal to mass depositing in the lungs at a unique c ritical MMAD. However, all of the inhaled fine particle definitions gi ve results much different from mass depositing in the lungs at MMADs a way from their critical MMADs, overestimating mass depositing in the l ungs by as much as 3.7 times and underestimating it by as much as 6.3 times. Although mass depositing in the lungs and the different fine pa rticle definitions are correlated over certain particle size ranges, n o correlation is valid over the entire particle size range considered. For reasonably polydisperse aerosols, inhaled fine particle mass stro ngly overemphasizes the benefits of MMADs in the 2-4 mu m range, since lung deposition is much less weakly dependent on MMAD than predicted by fine particle dose. (C) 1997 Elsevier Science Ltd.