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What Is Asthma
Asthma is a chronic lung condition. It is
characterized by difficulty in breathing.
People with asthma have extra sensitive or
hyperresponsive airways. The airways react by narrowing or
obstructing when they become irritated. This makes it difficult for
the air to move in and out. This narrowing or obstruction can cause
one or a combination of the following symptoms:
- wheezing
- coughing
- shortness of breath
- chest tightness
This narrowing or obstruction is caused by:
- Airway inflammation (meaning that the airways
in the lungs become red, swollen and narrow)
- Bronchoconstriction (meaning that the muscles
that encircle the airways tighten or go into spasm)
The incidence of asthma has risen dramatically in the past
20 years - a period too short to reflect any significant changes in the
gene pool. This supports the important role that environmental influences
(allergy, infection, lifestyle, and diet) have on the development of
asthma. Alternatively, this can be a result of better diagnosis.
Airways are the passages that carry air to the
lungs. As the airways progress through the lungs, they become
smaller, like branches of a tree. It is currently thought that
asthma produces its effects by leading to airway inflammation and
airflow limitation. This inflammation may even be present when a
person's asthma is asymptomatic (that is, when the person does not
have any symptoms).
When asthma is under control, as in the diagram on the left, the
airways are clear, and air flows easily in and out. When asthma is
not under control, the sides of the airways in the lungs become
inflamed and swollen, as in the diagram on the right. During an
attack, muscles around the airways constrict, and less air passes in
and out of the lungs. Excess mucus forms in the airways, clogging
them even further. The attack, also called an episode or
exacerbation, can include coughing, chest tightness, wheezing, and
difficulty breathing.
Asthma can be difficult to diagnose in infants, young children, the
elderly, smokers, workers exposed to chemical inhalants, people with
seasonal allergies, and people with recurrent acute respiratory
infections. Regular physical exams that include measurements of lung
function and evaluations of a patient's allergic status can help
ensure a proper diagnosis.
Risk factors for asthma include genetic
predisposition and environmental exposures, such as:
·
house dust mites
·
environmental tobacco smoke
·
cockroach allergen
However, just
because a person is at risk for a disease does not mean that he or
she will develop that disease. Being aware of the risk factors may
help people take precautions to avoid acquiring those diseases or
conditions. Other risk factors to asthma can cause someone with the
disease to have an exacerbation (worsening) of symptoms.
Genetic
Characteristics
Atopy is a genetic factor characterized by the body's production of
immunoglobulin E after exposure to common environmental allergens. A
person with high levels of IgE in the blood is more likely to have
an allergic response when exposed to certain substances in the
environment - so high levels of IgE may predict the
future development of asthma. If a person has a parent with asthma,
he or she is three to six times more likely to develop asthma than
someone who does not have a parent with asthma.
Environmental
Exposures
In 2000, the Institute of Medicine published the report
"Clearing the Air." This report reviews the evidence about indoor
air exposures and asthma as presented in the scientific literature.
The report looked at components that affected both the development
of the disease itself and the exacerbation of symptoms in someone
who already has the disease.
Clearing the Air: Categories for
Associations of Various Elements
The committee used a uniform set of categories to summarize its
conclusions about the association between exposure to indoor agents
and asthma. Focus on the first three categories.
- Sufficient evidence
of a causal relationship.
This means that the evidence is strong enough to document
that exposure to these substances causes the disease’s onset
or exacerbation.
- Sufficient evidence
of an association.
This means that the evidence is
strong enough to document an association between the agent
and the outcome has been observed in studies in which
chance, bias, and confounding factors can be reasonably
ruled out.
- Limited or suggested
evidence of an association.
This means that the evidence
suggests an association, but chance, bias, and confounding
factors cannot be ruled out with confidence.
Indoor Air
Exposures and Asthma Development
The Institute of Medicine committee concluded evidence was
sufficient to suggest a causal relationship between exposure to
house dust mite allergen and development of asthma in susceptible
children. It also found sufficient evidence of an association
between exposure to environmental tobacco smoke - also know as ETS
or secondhand smoke - in younger children and the development of
asthma. This includes both prenatal exposure to active maternal
smoking and ETS exposure after birth. Lastly, they found some
evidence to link asthma's development with exposure to cockroach
allergen in preschool-aged children, and with infections with
respiratory syncytial virus (RSV).
Clearing the Air: Indoor Air Exposures and
Asthma Exacerbation
Four exposures are considered causes of asthma exacerbations:
exposures to cat, cockroach, and house dust mite allergen, and
exposure of young children to ETS. Four additional exposures are
associated with worsening the disease: dog allergen, fungi or molds,
rhinoviruses, and a high level of exposure to nitrous oxides.
Evidence suggests an association between asthma exacerbations and
exposure to domestic birds, ETS in older children and adults,
formaldehyde, fragrances, and several respiratory infectious agents.
Links to more sites about asthma:
The Lung association -
http://www.lung.ca/asthma/
MedicineNet.com -
http://www.medicinenet.com/asthma/focus.htm
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