What is asthma?

Causes and Symptoms

Asthma is a Greek word meaning “gasping” or “panting.” It is a
chronic obstructive pulmonary (lung) disease that involves repeated attacks in
which the airways in the lungs are suddenly blocked. Asthma attacks cause the
affected person to experience tightening of the chest, sudden breathlessness,
wheezing, and coughing. Death by asphyxiation is rare but possible. Fortunately,
the effects can be controlled with proper medication. The severity of symptoms and
attacks varies greatly among individuals, and sufferers can be categorized in one
of four classes: intermittent, mild persistent, moderate persistent, and severe
persistent. Mild persistent asthma is characterized by fewer than six minimal
attacks per year, no symptoms between attacks, and no hospitalizations and little
or no medication between attacks. Severe persistent asthma is characterized by
more than six serious attacks each year, symptoms between attacks, more than ten
missed school days or workdays, and two or more hospitalizations per year. Attacks
are typically spaced with symptom-free intervals but may also occur continuously.
Rather than focusing only on the specific attacks, one should view and treat
asthma as a chronic disease that persists over a long period of time.

A review of the path of air into the body during normal breathing helps in
understanding asthma. During inhalation, air travels into the nose and mouth and
then into the trachea (windpipe); it then divides into the two tubes called
bronchi and enters the lungs. Inside each lung, the tubes become smaller and
continue to divide. The air finally moves into the smallest tubes, called
bronchioles, and then flows into the millions of small, thin-walled sacs called
alveoli. Vital gas exchange occurs in the alveoli.

This gas exchange involves two gases in particular, oxygen and carbon dioxide.
Oxygen must cross the membrane of the alveoli into the blood and then travel to
all the cells of the body. Within the cells, it is used in chemical reactions that
produce energy. These same reactions produce carbon dioxide as a by-product that
is returned by the blood to the alveoli. This gas is removed from the body through
the same pathway that brings oxygen into the lungs.

The parts of this airway that are involved in asthma are the bronchioles. These
tubes are wrapped with smooth, involuntary muscles that adjust the amount of air
that enters. The lining of the bronchioles also contains many cells that secrete a
substance called mucus. Mucus is a thick, clear, slimy fluid produced in many
parts of the body. Normal production of mucus in the lungs catches foreign
material and lubricates the pathway to allow smooth airflow. People suffering from
asthma have very sensitive bronchioles.

Three pathological processes in the bronchioles contribute to an asthma attack.
One is an abnormal sensitivity and constriction of the involuntary muscles
surrounding the airway, which narrows the diameter of the airway. Another is an
inflammation and swelling of the tissues that make up the bronchioles themselves.
The third is an increased production of mucus, which then blocks the airways.
These three mechanisms may work in combination and are largely caused by the
activation of mast cells in the airways. The result can be extreme difficulty in
taking air into the lungs until the attack subsides. The characteristic “wheeze”
of asthma is caused by efforts to exhale, which is more difficult than inhaling.
In the most serious attacks, the airways may close down to the point of
suffocating the patient if medical help is not given.

Attacks can vary in severity at different times because of variations in tension
within the bronchiole muscles. Although there is still debate about the general
function of these muscles, they probably help to distribute the air entering the
alveoli evenly. Control of the tension in these smooth muscles is involuntary and
follows a circadian (twenty-four-hour) rhythm influenced by neurohormonal control.

Following a given asthma attack, patients are sometimes susceptible to additional,
more severe attacks. This period of high risk, called a "late-phase response,"
occurs five or six hours after the initial symptoms pass and may last as long as
several days.

The initial cause and mechanism of an asthma attack can vary from person to
person. Accordingly, asthma is usually divided into two types. One type is
extrinsic—that is, caused by external triggers that bring about an allergic
response. Allergic reactions involve the immune
system. Normal functioning of the immune system guards the body
against harmful substances. With an allergy, the body incorrectly identifies a
harmless substance as harmful and reacts against it. This substance is then called
an allergen. If the symptoms of this reaction occur in the lungs, the person has
extrinsic or allergic asthma.

Researchers have discovered that many people with asthma have elevated levels of
immunoglobulin E (IgE), a substance that indicates an allergic reaction within the
body. Allergic triggers for asthma include dust, pollens, mold, animal dander, and
other substances. Infants may have an IgE response to respiratory syncytial virus.
Improved asthma treatments may lie in substances that interfere with interleukin-4
(IL-4), which promotes IgE production in the body.

When allergens enter the body, the white blood cells make specific IgE antibodies
that can bond with the invaders. Next, the IgE antibodies attach to the surfaces
of mast cells; these cells are found all over the body and are numerous in the
lungs. The allergens attach to the IgE antibodies located on the mast cells, and
the mast cells are stimulated to produce and release chemicals called mediators,
such as histamine, prostaglandin D2, and
leukotrienes. These mediators cause sneezing, tighten the muscles in the
bronchioles, swell the surrounding tissues, and increase mucus production.

The second type of asthma is intrinsic and does not involve allergies. People who
suffer from intrinsic asthma have hyperactive airways that overreact to irritating
factors. The mechanism for this form is not clearly understood, but no IgE
antibodies for the irritant are placed on the mast cells. Examples of such
nonallergic stimuli are cigarette smoke, house dust, artificial coloring, aspirin,
ozone, or cold air. Insecticides, cleaning fluids, cooking foods, and perfume can
also trigger attacks. Also included in this category are attacks that are caused
by viral
infections (including colds and flu), stress, and exercise.
Asthma can be triggered by many different substances and events in different
people. While the symptoms are the same whether the asthma is intrinsic or
extrinsic, individuals with asthma need to identify what substances or events
trigger their attacks in order to gain control of the disease.

In addition to tightening of the chest, sudden breathlessness, wheezing, coughing,
and chest pain common to an asthma attack, symptoms of a severe attack include
rapid pulse, blue lips or skin, perspiration, anxiety, or extreme fatigue.

Why people develop asthma is not well understood. Asthma can begin at any age, but
it is more likely to arise in childhood. While it is known that heredity
predisposes an individual to asthma, the pattern of inheritance is not a simple
one. Most geneticists now regard allergies as polygenic, which means that more
than one pair of genes is involved. Exposure to particular external conditions may
also be important. Boys who develop asthma are more likely to display symptoms in
childhood, while girls are more likely to show signs of the disease at puberty
(about age twelve). Childhood asthma is also most likely to disappear or to be
“outgrown” at puberty; about half of the cases of childhood asthma eventually
disappear.

Early exposures to some triggers may be a key in the development of asthma.
Increasingly, studies indicate that air pollution is an important risk
factor for developing asthma, especially in children. Smoking by mothers during
and after pregnancy can cause children who have a genetic disposition to develop
asthma, as early exposure to secondhand smoke can cause an allergy
to develop. Early studies in this area were confusing until the data were sorted
by level of education. Lung specialist Fernando Martinez of the University of
Arizona believes that less-educated women who smoke are more likely to cause this
effect because their homes tend to be smaller and therefore expose the children to
more concentrated levels of smoke. Early exposure by genetically susceptible
children to dust and dust mites may also cause some to develop asthma. Exposure to
chemicals in utero is also a risk factor for developing asthma. Lower respiratory
infections early in life are also associated with an increased risk for asthma.
Being overweight or obese also increases the risk of developing asthma.

While attacks can cause complications, there is no permanent damage to the lungs
themselves. Complications include possible lung collapse, infections, chronic
dilation, rib fracture, a permanently enlarged chest cavity, and respiratory
failure. However, millions of days of work and school are lost as individuals
recuperate from attacks; asthma is the leading cause of missed school days. Even
though attacks can be controlled by medication, fatalities do occur. In the United
States, there are more than three thousand deaths due to asthma each year.

Treatment and Therapy

The key to gaining control of asthma is discovering the particular factors that
act as triggers for an attack in a given individual. These factors vary and at
times can be surprising; for example, one person found that a mint flavoring in a
particular toothpaste was a trigger for his asthma. Nevertheless, most common
triggers fall in the following groups: allergies; irritants, including dust,
fumes, odors, vapors, molds, mildew, and red tide; air pollution, weather and
temperature changes, and dryness; colds, flu, and other viral infections; and
stress. Even types of food may be important. Diets low in vitamin C, fish, or a
zinc-to-copper ratio, as well as diets with a high sodium-to-potassium ratio, may
increase the risk of asthma attacks and bronchitis. There have also been
correlations between low niacin levels in the diet and tight airways and wheezing.
Food
allergies and sulfites, chemical preservatives found in wine
and dried fruits, may also act as triggers.

Diagnosis of asthma is based on medical history, a physical examination, and
spirometry. Some doctors supplement their diagnosis of
asthma with a tool called the "peak flow meter," which measures peak expiratory
flow rate. The meter can also be used by patients at home to predict impending
attacks. This inexpensive device measures how quickly air can be moved out of the
lungs. Therefore, it can be discovered that airways are beginning to tighten
before other symptoms occur. The early warning allows time to adjust medications
to head off attacks. This tool can help individuals with asthma take charge of
their disease.

Various medications are available to keep the airways open and to lower their
sensitivity. In an emergency, drugs may be injected, but medications are usually
either inhaled or taken orally as pills. Because inhalation transports the
medication directly to the lungs, lower doses can be used. Individuals with asthma
should carry inhalers, which allow them to breathe in medication such as
short-acting beta agonists (SABA) during an attack. Because this action requires a
person to coordinate inhaling with the release of the spray, young children are
sometimes better off with a device that requires them to wear a mask. The choice
and dosage of medicine vary with the patient, and physicians need to determine
what is safest and most effective for each individual.

The treatment of asthma is based on a stepwise management approach. The National
Heart, Lung, and Blood Institute recommends individuals with intermittent asthma
to use SABA as needed; for exacerbations due to viral infections, individuals with
intermittent asthma may need to use SABA every four to six hours. Oral systemic
corticosteroids may also be prescribed to treat moderate to severe exacerbations.
For individuals with persistent asthma, the recommended treatment begins with
low-dose inhaled corticosteroids (ICS); subcutaneous or sublingual
immunotherapy may be considered for individuals with allergic
asthma. Low-dose ICS plus long-acting beta-2 agonists (LABAs) or medium-dose ICS
alone may be used if low-dose ICS is insufficient. High-dose ICS and LABA may be
used to treat more severe cases of asthma; omalizumab may be considered for
patients with allergies.

Some of the common prescribed drugs are bronchodilators, inflammation reducers,
and trigger-sensitivity reducers. The bronchodilators include albuterol. These are
beta-agonists that mimic the way in which the body’s nervous system relaxes or
dilates the airways. (Any drug that functions as a beta-blocker should be avoided
by people with asthma because of its opposite effects.) Cromolyn and nedocromil
act as mast-cell stabilizers and may be considered as an alternative treatment
method. Injections of omalizumab (Xolair) may be prescribed in combination with
other medications to control difficult-to-treat cases.

The use of inflammation reducers known as corticosteroids plays an important role in the treatment of
asthma. Whether administered orally or via an inhaler, these medications can both
prevent and treat the airway inflammation that leads to asthma attacks. Their
anti-inflammatory effects mean fewer symptoms and attacks, better airflow, and
airways that are less likely to react to triggers in an exaggerated or
hyperresponsive manner. Inhaled steroids are preferred for long-term management of
asthma. Inhalation delivers the medication directly to the site of inflammation
and is associated with fewer side effects, which can include osteoporosis,
thinning and easily bruised skin, cataracts, and suppression of the
adrenal
glands. However, oral steroids may also be used in the
treatment of moderate to severe persistent asthma, and short courses of oral
corticosteroids may be used during periods of sudden, life-threatening symptoms.
To minimize possible side effects, oral steroids are given every other day or in
decreasing dosage over a limited period of time. Calcium and vitamin D supplements
are used to prevent bone loss in these patients.

Individuals should not exceed their prescribed dosage when using an inhaler. An individual who feels the need to use an inhaler more often to obtain adequate relief should see a doctor. The increased need is a sign of worsening asthma, and a doctor needs to investigate and perhaps change the treatment.

Drugs that interfere with the chemical moderators such as leukotriene have also been approved for treatment. Zileuton (Zyflo) interferes with leukotriene production in the mast cells. Montelukast sodium (Singulair) blocks the actions of leukotrienes as they attach to receptors on the outside of airway cells and turn on the cellular responses that lead to the asthma reaction: contraction of the airway muscles, swelling of the airway lining, and flooding of the remaining airway space with sticky mucus.

With a doctor’s approval, regular sports and exercise may be pursued. Furthermore,
exercise may be helpful in reducing the frequency and severity of attacks. Many
athletes compete at high levels in spite of their asthma. Sports that do not
require continuous activity or exposure to cold, dry air are preferred. Swimming
is considered ideal. Doctors can help the athlete with a pre-exercise medication
plan and a backup plan if symptoms occur during or after the exercise.

Individuals with asthma are advised to avoid allergens and other asthma triggers
and to consider installing air conditioning and HEPA air filtering
units. Breathing techniques and written emotional disclosure may also offer
relief.

Perspective and Prospects

In the United States, asthma prevalence has increased from 7.3 percent in 2001 to
8.4 percent in 2010, according to the US Centers for Disease Control and
Prevention. An estimated 25.7 million persons had asthma in the United States in
2010. Asthma prevalence is higher among individuals with family incomes that are
below the poverty level. Despite the rising incidence of asthma, asthma death
rates per one thousand persons with asthma have declined from 2001 to 2009;
nevertheless, asthma deaths rates per one thousand persons with asthma were higher
for women, black persons, and the elderly.

According to the World Health Organization, an estimated 235 people worldwide
suffer from asthma, representing the most common chronic disease among children.
More than 80 percent of asthma deaths occur in low- and lower-middle-income
countries, where asthma is often underdiagnosed and undertreated.

Bibliography

American Lung Association. http://www.lung.org.

American Medical
Association. Essential Guide to Asthma. New York: Pocket,
2000. Print.

Bernstein, Jonathan A., and Mark L. Levy,
eds. Clinical Asthma: Theory and Practice. Boca Raton: CRC,
2014. Print.

Bislimi, Adelina H., and Lulezime C.
Tolka, eds. Asthma: Causes, Complications, and Treatment.
New York: Nova Science, 2012. Print.

Clark, T. J. H., et
al., eds. Asthma. 4th ed. New York: Oxford UP, 2001.
Print.

Currie, Graeme P., and John F. W. Baker.
Asthma. 2nd ed. Oxford: Oxford UP, 2012.
Print.

Haas, François, and
Sheila Sperber Haas. “Living with Asthma.” The World Book Medical
Encyclopedia. Chicago: World Book, 1988. Print.

Judd, Sandra J. Asthma
Sourcebook. 3rd ed. Detroit: Omnigraphics, 2012.
Print.

Krementz, Jill.
How It Feels to Fight for Your Life. Boston: Little,
Brown, 1989. Print.

Lockey, Richard F., and Dennis K. Ledford.
Asthma: Comorbidities, Coexisting Conditions, and Differential
Diagnosis. Oxford: Oxford UP, 2014. Print.

Lotvall, Jan, ed. Advances in
Combination Therapy for Asthma and COPD. Chichester: Wiley,
2012. Print.

Ostrow, William, and
Vivian Ostrow. All About Asthma. Morton Grove: Whitmany,
1989. Print.

Parker, James M., and
Philip M. Parker, eds. The Official Patient’s Sourcebook on
Asthma. Rev. ed. San Diego: Icon Health, 2005. Print.

Welch, Michael J., and
the American Academy of Pediatrics. American Academy of Pediatrics
Guide to Your Child’s Asthma and Allergies: Breathing Easy and Bringing
up Healthy, Active Children. New York: Random, 2000.
Print.