Inertial sizing of aerosol inhaled during pediatric tidal breathing from an MDI with attached holding chamber

Abstract

A procedure that allows cascade impaction to be used to measure the particle size distribution of the aerosol inhaled from a holding chamber with a square wave tidal breathing pattern is described. A constant flow rate of 28.3 l/min occurs through an Anderson impactor while tidal breathing occurs through the holding chamber by using a two-way valve system and a piston connected to a computer controlled stepper motor. Replicas of infant (7 months old) and child (4 years old) faces are used to allow collection of the aerosol at the entrance to simulated nostrils during tidal breathing at flow rates and tidal volumes near predicted values for these ages. Ventolin ® and Beclovent ® MDIs with the Space-Chamber ® holding chamber (with infant or pediatric mask) are tested. Although significantly less drug ( P<0.01) is inhaled with the infant face replica than the child face replica or the adult-mouthpiece study of Finlay et al. (1997), these differences are largely due to differences in amounts inhaled in large particles, since no significant difference is found in the amount inhaled in particles <2.1 μm for salbutamol or <3.3 μm for beclomethasone between the infant, child or adult-mouthpiece results. These results indicate that caution may be needed when evaluating holding chambers using in vitro data on total mass inhaled, since differences can be caused by differences in large particles that do not contribute significantly to lung deposition.