Modeling Deposition of Inhaled Particles - Aerosols: Measurement, Dosimetry, and Health Effects - page 104

5.4.8 a ge
Age can be a signiicant factor inluencing the deposition and distribution of particles in the human
lung, likely due to the differences in airway geometry and ventilation between children and adults.
Studies of airway geometry as a function of age are presented by Ménache and Graham, 241 Hofmann
et al., 242 and Martonen et al. 243 Age has also been shown to affect a percentage of nasal breathing, 244
thus affecting an amount of particulate matter that makes it to the human lung. Bennett et al. 245
showed that children have enhanced upper airway deposition of coarse particles when compared to
adults, but that total deposition amounts are comparable.
Several studies have modeled aerosol deposition as a function of human subject age. Martonen
et al. 242 found that modeled total deposition within the human lung decreased with increasing age from
7 months to 30 years. In addition, Isaacs and Martonen 246 compared modeled lung deposition results
for children with available experimental data. Using the International Commission on Radiological
Protection (ICRP) 66 model, 21 Harvey and Hamby 247 found that for 1 μm particles, deposition and
regional distribution varied by age, with extrathoracic deposition increasing signiicantly in younger
age groups (young children and infants) that have smaller respiratory airway sizes. Hofmann et al. 243
showed that particle deposition does indeed depend on lung morphology and that dose per surface
area decreases from 7 months of age to adulthood.
The U.S. EPA has also identiied children as a sensitive subpopulation requiring additional
consideration in the establishment of air quality standards. 240 Therefore, the development of particle
deposition models for children is of particular importance. A model of particle deposition in a
developing human lung has also been developed. 248 It was predicted that children may receive a
localized PM dose three times that of adults. Such models will be of great use in both inhalation
toxicology and inhalation therapy.
5.5 THEORY AND EXPERIMENT
Many different types of experimental protocols have been developed to measure particle deposition
in the respiratory system. An overview of several of these methods will be presented, and a discus-
sion of how the resulting data can be compared with particle deposition will be presented.
5.5.1 P redictions oF P article d ePosition
Simulation studies can be used to predict the deposition of inhaled particles on differing spatial
scales of resolution. Models can be developed that predict total respiratory system deposition or
deposition in each of the regional (i.e., extrathoracic, TB, or pulmonary) compartments. In addition,
models can predict deposition eficiencies in each individual airway generation or simulate the dose
to a speciic anatomical location (e.g., a carinal ridge or airway wall) within a respiratory passage.
The level of detail desired and the type of experimental data available for model validation should
govern the selection or development of an appropriate model for a given research purpose.
5.5.2 P article d ePosition M easureMents
Much work has been done in attempting to quantify the deposition of particles in respiratory air-
ways, encompassing a wide range of approaches and techniques. We provide an overview of aerosol
deposition measurements that have been performed in casts, animal models, and human subjects.
Comprehensive reviews of experimental measurements of respiratory particle deposition have been
presented by Martonen, 8 Sweeny and Brain, 249 and Kim. 250
5.5.2.1 Casts and Models
Particle deposition measurements have been performed in models and replica casts of both human
and animal lungs. Such studies provide a means of examining particle deposition airway by airway