INERTIAL SIZING OF AEROSOL INHALED DURING PEDIATRIC TIDAL BREATHING FROM AN MDI WITH ATTACHED HOLDING CHAMBER

A procedure that allows cascade impaction to be used to measure the pa rticle size distribution of the aerosol inhaled from a holding chamber with a square wave tidal breathing pattern is described. A constant f low 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 u sed to allow collection of the aerosol at the entrance to simulated no strils during tidal breathing at flow rates and tidal volumes near pre dicted values for these ages. Ventolin(R) and Beclovent(R) MDIs with t he Space-Chamber(R) holding chamber (with infant or pediatric mask) ar e tested. Although significantly less drug (P < 0.01) is inhaled with the infant face replica than the child face replica or the adult-mouth piece study of Finlay et al. (1997, these differences are largely due to differences in amounts inhaled in large particles, since no signifi cant difference is found in the amount inhaled in particles < 2.1 mu m for salbutamol or < 3.3 mu m for beclomethasone between the infant, c hild 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 depositio n. (C) 1998 Elsevier Science B.V. All rights reserved.