087 Comparison of methods for cascade impactor data analysis to predict aérosol déposition into patient airways

Abstract

Cascade impactors are the most widely encounte-red means to measure aerosol particle size distribution produced by nebulizers. The usual method used to treat particle size data was compared to a new method (calibration method) which is not based on a specifie hypothesis, contrary to the usual method which assumes that cascade impactor collection efficiency is ideal. Four nebulizers (Multisonic ® , Sidestream ® , Aeroneb Go ® , PariLC+ ® ) were used to produce NaF aerosols, and particles size was measured with the 8-stage Marple Model 290 Personal cascade impactor. The usual method consists in plotting the mass fraction (F j ) deposi-ted on each stage us. the cut-offdiameter (De j ) corresponding to the stage. According to the European Standard (EN13544-1), a best-fit curve links the points De j , F j . This work develops another method of particle size data processing based on cascade impactor calibration, which takes into account imperfect stage collection efficiency. To calibrate the impactor, monodisperse aerosols of diameter Dcalj (i = 1 to m) were generated, and the mass fraction deposited on each stage was measured. The mass fraction of monodisperse aerosols of diameter Dcalj deposited on impactor stage De j is f i,j ;. Values of F j and f i,j j can be represented by mathematical matrix. To obtain the corrected distribution of aerosol, matrix containing f-: values is multiplied by matrix contai-ning Fj values. The curve linking the points (X-axis = Monodisperse aerosol diameters Dcal j ; Y-axis = corrected distribution) is then plotted. Values of Mass Median Aerodynamic Diameters and Respiratory Fractions (%l-5 μm) for the usual and calibration methods are summarized in the table below. The highest differences were observed for Sidestream and PariLC+ ® nebulizers. Impactor calibration must be done with many monodisperse aerosols so that calibration method gives more precise calculations of MMAD and respiratory fractions than usual method.