Chronic Lung Disease
- Asthma is a chronic disorder of the airways that is complex and characterized by variable
and recurring symptoms, airflow obstruction, bronchial hyperresponsiveness, and an
underlying inflammation .
- Asthma is one of the most common chronic disorders affecting children, and the
prevalence (the percentage of the population that has a condition at a specific point
in time) of asthma remains at historic high levels since the late 1990s.
- Boys more commonly have asthma than girls, but during adolescence the prevalence of
asthma in girls is similar to that of boys.
- Asthma has a significant impact on children and their families.
Etiology and Pathophysiology
- Asthma is a chronic inflammatory disease of the lungs in children who are
- It is caused by the interplay of multiple factors, including indoor air contaminants
(e.g., tobacco smoke, pet dander, and cockroach feces), outdoor air pollutants,
recurrent respiratory viral infections, and allergic disease (e.g., atopic eczema, hay fever,
and food allergies).
- Protective factors that reduce the risk for asthma include a large family size, later birth
order, childcare attendance, dog in the family, and living on a farm.
- According to the hygiene hypothesis, these protective factors increase exposure to
infections in early life that enable the child’s immune system to develop along a
- Inflammation causes the normal protective mechanisms of the lungs (mucous formation,
mucosal swelling, and airway muscle contraction) to overreact in response to a
stimulus and cause an acute asthma episode (sudden onset of breathing difficulty with
cough, wheeze, or breathlessness) and airway obstruction.
- The trigger, a stimulus initiating an acute asthma episode, can be inflammatory or
- Triggers increase the frequency and severity of smooth muscle contraction
(bronchospasm), and airway responsiveness is enhanced through inflammatory
- Asthma triggers include exercise, viral or bacterial agents, allergens (mold, dust,
pollen, furry pets, birds), fragrances, food additives, pollutants, weather changes
(humidity and temperature), and emotions or stress.
- With exposure to a trigger, IgE and sensitized mast cells may be activated, leading to
the release of many inflammatory mediators (e.g., histamines, prostaglandins, and
leukotrienes). - The inflammatory mediators release pro-inflammatory cytokines, causing chronic
airway inflammation that may be associated with airway remodeling (permanent airway
damage that involves thickening of the sub basement membrane, subepithelial
fibrosis, airway smooth muscle hypertrophy and hyperplasia, blood vessel proliferation
and dilation, and mucous gland hyperplasia and hypersecretion).
- This results in decreased airway elasticity and decreased lung function. These
permanent alterations are not prevented by or fully responsive to currently available
treatments. The reactive airway responses to stimu