Low-flow cascade impaction

Low-flow cascade impaction may have other technical advantages. The MMAD is often used to predict deposition in the human lung. However, many aerosols change their aerodynamic characteristics in real time after they are generated. For example, particles from MDIs may be nuxed with volatile com-... 

A draft European Nebulizer Standard (30) has been submitted for formal approval to CEN (Comite Europeen de Normalisation European Committee for Standardization). CEN is responsible for European standardization in all fields except Electrotechnical (CENELEC) and Telecommunications (ETSl). Publication of the European Nebulizer Standard is expected during 2001. Included within the European standard are detailed descriptions of two test methods for (1) assessing nebulizer aerosol output inhaled using breath simulation similar to that described previously and (2) assessing nebulized aerosol droplet size using low-flow cascade impaction. Because this standard is expected to be adopted throughout Europe (and possibly more widely), a summary of its contents may be useful to readers. 

Aerosol Size Measurement Using Low-Flow Cascade Impaction... 

This low-flow cascade impaction method differs in a subtle but important manner from methods described earlier (Chap. 8, Fig. 7) in which the low-flow cascade is incorporated within a simulated breathing pattern. Here the cascade samples at a relatively low constant flow (2 L/min) within a sinus flow... 

A low-flow cascade impactor can be inserted into the ventilator circuit between the distal tip of the endotracheal (or tracheostomy) tube and the inhaled mass filter. Impaction experiments have repeatedly shown that the aerosols leaving the tube and entering the patient are similar to those produced by small-particle nebulizers such as the AeroTech n. Often the MMADs are about 1.0 pm (27). 

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