Growth of nasal and laryngeal airways in children: implications in breathing and inhaled aerosol dynamics.

BACKGROUND The human respiratory airway undergoes dramatic growth during infancy and childhood, which induces substantial variability in air flow pattern and particle deposition. However, deposition studies have typically focused on adult subjects, the results of which cannot be readily extrapolated to children. We developed models to quantify the growth of human nasal-laryngeal airways at early ages, and to evaluate the impact of that growth on breathing resistance and aerosol deposition. METHODS Four image-based nasal-laryngeal models were developed from 4 children, ages 10 days, 7 months, 3 years, and 5 years, and were compared to a nasal-laryngeal model of a 53-year-old adult. The airway dimensions were quantified in terms of different parameters (volume, cross-section area, and hydraulic diameter) and of different anatomies (nose, pharynx, and larynx). Breathing resistance and aerosol deposition were computed using a high-fidelity fluid-particle transport model, and were validated against the measurements made with the 3-dimensional models fabricated from the same airway computed tomography images. RESULTS Significant differences in nasal morphology were observed among the 5 subjects, in both morphology and dimension. The turbinate region appeared to experience the most noticeable growth during the first 5 years of life. The nasal airway volume ratios of the 10-day, 7-month, 3-year, and 5-year-old subjects were 6.4%, 18.8%, 24.2%, and 40.3% that of the adult, respectively. Remarkable inter-group variability was observed in air flow, pressure drop, deposition fraction, and particle accumulation. The computational fluid dynamics predicted pressure drops and deposition fractions were in close agreement with in vitro measurements. CONCLUSIONS Age effects are significant in both breathing resistance and micrometer particle deposition. The image/computational-fluid-dynamics coupled method provides an efficient and effective approach in understanding patient-specific air flows and particle deposition, which have important implications in pediatric inhalation drug delivery and respiratory disorder diagnosis.