RESUMO
A procedure is developed that allows particles inhaled with realistic breath patterns to be sized by cascade impaction at a constant flow rate. This procedure is then used to examine the difference between particle sizes obtained with constant flow rate (step profile) versus actual-subject breath patterns for two dry powder inhalers DPIs: the Ventodisk and Spiros inhalers (delivering salbutamol sulphate). Aerosol inhaled from the DPIs by a breath simulator was combined with make-up air to provide 300 l/min. to a pair of virtual impactors. These impactors separate out particles in the nominal diameter range of 1-10 microm for sizing at 30 l/min. by a MOUDI cascade impactor, with filter collection of particles outside this range. Breathing patterns of ten subjects ranging in age from 6 to 17 years of age were measured and recorded using whole-body plethysmography while these volunteers inhaled through Ventodisk and Spiros inhalers. Particle sizes with four of these breath patterns, as well as several constant flow rate step profiles, were then obtained using the sizing apparatus with a realistic mouth throat intake. Our results show that as long as the constant flow rates were near typical values occurring in the actual-subject breaths, particle sizes obtained with constant flow rates were not significantly different (P > 0.01) from those occurring with actual-subject breath patterns. Significant differences are present if constant flow rates unrepresentative of those expected during particle uptake with the actual-subject patterns are used with the Ventodisk. These results show that judiciously chosen constant flow rates give rise to inertial particle size measurements that are equivalent to those obtained during actual-subject inhalation for the two types of DPIs tested.
