Environmental Engineering Reference
In-Depth Information
Chronic bronchitis is characterized by excessive mucus generation and alveolar wall thickening.
The excessive mucus is a result of hypertrophied mucus glands, and causes the formation of mucus
plugs that obstruct airways and may fully occlude small bronchi. Alveolar wall thickening results in
reduced elasticity of alveolar walls, limiting regional ventilation. 117,168
5.4.7.2  Asthma
Asthma is characterized by a reduction of the airway lumen due to constriction of the bronchial air-
ways in response to a stimulus. This constriction may also in turn result in an increase in the mucus
layer thickness. Chronic asthma can result in subepithelial ibrosis. 168 Asthma stimuli may include
pollutants, allergens, or exercise. It has been noted that asthma has attained epidemic proportions
on a global scale. 223
5.4.7.3  Cystic Fibrosis
CF is a genetic disease that causes the lung's epithelial cells to produce abnormally thick, excessive
mucus. This slowly cleared mucus narrows airways and obstructs airlow making tissue vulnerable
to inlammation and recurrent infection. This inlammation and infection causes progressive respi-
ratory disease including bronchiectasis and chronic airway obstruction. 168,224 Impairment typically
begins in the small airways and progresses proximally, with ventilation increasingly shifting from
obstructed regions to healthy regions of the lung. 225
5.4.7.4  Effect of Obstructive Disease on Particle Deposition and Distribution
Several studies have investigated the effect of obstructive disease on particle deposition and dis-
tribution in the human lung. Exploring the effect on particle deposition, Kim and Kang 226 found
a marked increase in deposition of 1 μm particles in patients with COPD and asthma compared to
normal subjects. Anderson et al. 227,228 found that the deposition of ine and ultraine particles was
increased in patients with CF and obstructive disease. Brown et al. 130 found that COPD patients
had a greater dose rate for ultraine particles than healthy subjects. Also, the deposition of particles
increased with severity of obstruction or decrease in lung function. 225,229-231 Reasons for increased
deposition in patients with obstructive disease include (1) reduction of airway diameter by constric-
tion or mucus buildup, thus increasing inertial impaction on airway walls, (2) increased residence
time of particles in the alveolar region resulting from nonuniform ventilation distribution, (3) col-
lapse of airways due to low limitation, and (4) low perturbations or induced turbulence at sites of
obstruction. 225,226,228
Investigating the effect of obstructive disease on particle distribution, Brown et al. 232 found that
a signiicant number of coarse particles deposit in the poorly ventilated TB airways of CF patients,
while these particles follow regional ventilation in healthy subjects. Other studies indicate that
the deposition pattern of particles in patients with obstructive disease is heterogeneous, with an
enhancement of deposition in various local regions. 233-235
5.4.7.5  Modeling Disease
Several models of particle deposition have been developed that speciically address disease. Segal
et al. 236 modeled particle deposition in patients with COPD, using a modiied deterministic model. 7,32
This work investigated the dependence of deposition pattern on the severity of disease. In addition,
Martonen et al. simulated particle deposition in CF. This study found a proximal shift in particle
deposition with severity of obstruction. 237-239 More recently, Martonen et al. 223 have simulated the
effect of asthma on particle deposition patterns, comparing their results with data from imaging
studies of asthma patients.
The United States Environmental Protection Agency (U.S. EPA) has identiied people suffer-
ing from respiratory disease as a sensitive subpopulation needing particular consideration in risk
assessment of particulate matter and in the establishment of air pollution standards. 240 Therefore,
more advanced models of particle deposition for a variety of diseases are needed.
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