- • Cough, shortness of breath, wheezing, and chest
discomfort, often in association with triggering factors.
- • Wheezing, diminished breath sounds, hyperinflated
lung fields, hyperresonance to percussion; examination can be normal.
- • Variable degrees of airflow limitation, improvement
in airflow following bronchodilator therapy, airtrapping, and airways
Asthma is a chronic inflammatory condition of the lungs. It has
no known distinct etiology, and there are many different clinical
manifestations, making asthma a syndrome rather than a specific disease.
Asthma affects approximately 7% of the U.S. population,
both adults and children, resulting in 17 million people with asthma
in the United States, and over 100 million worldwide. The socioeconomic
burden of asthma is high, with over 11 billion dollars spent in
total costs in 1998, including billions of dollars in indirect costs
from lost productivity. The prevalence of asthma is increasing worldwide,
having risen approximately 75% over the years 1980–1994
in the United States. The reasons for this increase are likely due,
in part, to increased exposure of susceptible individuals to indoor
air pollutants or allergens, and perhaps also to a changing microbiological environment
that impacts immune system development. The National Institutes
of Health (NIH) and World Health Organization (WHO) have issued
disease management guidelines to assist in the consistent diagnosis
and treatment of asthma, but dissemination of these guidelines to
the medical community is incomplete.
The inflammation involved in asthma extends throughout the respiratory
tree (Figure 6–1). The clinical manifestations
of asthma are a consequence of the effects of this inflammation
on the airways and surrounding lung parenchyma, resulting in airway
narrowing, airflow limitation, and alterations in lung mechanics.
Overview of asthma pathophysiology. A: Biology.
The biology of asthma involves the release of mediators, cytokines,
and other signals from activated inflammatory cells, resulting in
airway smooth muscle constriction, pulmonary vascular dilation and
leakage, and mucous gland secretion. Over time, these processes
result in airway remodeling. Macs, macrophages; eos, eosinophils;
pmns, polymorphonuclear leukocytes; lymphs, lymphocytes; TH1, TH2,
T-helper cell type 1, 2. See text for details. B: Anatomy.
Airway remodeling is seen by airway wall thickening from inflammatory
cell infiltration, airway edema, increased mucus secretion, subepithelial
fibrosis and increased smooth muscle mass. In addition, there may
be a loss of the linkage between the airway wall and surrounding tethering
elements of the alveoli. C: Physiology.
The physiological effects of the narrowed, thickened airways are
airflow limitation and gas trapping, resulting in hyperinflation. D: Symptoms. The symptoms arising
from these underlying pathophysiological changes include wheezing,
cough, dyspnea, and chest discomfort.
Many patients with asthma exhibit a two-phase response when exposed
to allergen, and this response pattern serves as a useful paradigm
to characterize the inflammatory events that are thought to occur.
Initially, upon exposure to a sensitizing stimulus in a susceptible
individual, mast cells and epithelial cells within the airway are ...