In vitro deposition measurement of inhaled micrometer-sized particles in extrathoracic airways of children and adolescents during nose breathing

An in vitro study was conducted with the goal of developing empirical correlations to predict the deposition of particles with an aerodynamic diameter of 0.5-5.3 mu m in nasal airways of children with ages 4-14 years. CT images of nasal airways of thirteen healthy subjects and one with congested nasal airways were used for fabricating the replicas by rapid prototyping. Replicas included nasal airways to the level of the upper trachea as well as the face. Four physiological breathing patterns (sinusoidal waves) of children were simulated by a pulmonary waveform generator. Using an Electrical Low Pressure Impactor (ELPI) we measured deposition of sunflower oil particles generated by a Collison atomizer. Moreover, using the same setup, particle deposition in five adult replicas fabricated using MRI images was measured for direct comparison with the child replicas and in vivo data available for adults. Deposition increased by increasing particle size and flow rate, indicating impaction as the dominant deposition mechanism. Existing correlations for adults were unable to reduce the scatter in the deposition data for children. A correlation was developed for prediction of deposition including the relevant non-dimensional numbers (Stokes and Reynolds numbers) that were calculated considering the dimensions of the airways. The corrected correlations should be useful for exposure estimation of children and for efficient pediatric drug delivery using face masks. (C) 2011 Elsevier Ltd. All rights reserved.