Asthma is an immunological
disease which causes difficulty in breathing. It is a form of
hypersensitivity in which the bronchioles in the lungs are narrowed by
inflammation and spasm of the lining of the airway wall. A person with
asthma may experience wheezing, shortness of breath and poor exercise
tolerance. Sudden attacks of breathlessness may require hospitalization and
can lead to rapid deterioration. Treatment of asthma is with medication,
inhaled or in the form of tablets.
Signs and symptoms
cardinal symptom of asthma is wheezing (shortness of breath), indicating
airway obstruction. Cough, sometimes with clear sputum may be present.
Typically the symptoms are very variable, and associated with the triggers
listed above. Symptoms are often worse during the night or on waking.
Asthma sometimes correlates with acid indigestion, especially amongst older
Signs of asthma are rapid
breathing, expiratory (breathing out) phase of breathing longer than
inspiratory (breathing in), drawing in of tissues between ribs and above
sternum & clavicles, inflation of the chest and bronchi (wheezy noises
heard with a stethoscope). In severe attacks the asthma sufferer may be
cyanosed (blue), may have chest pain and can lose consciousness. Between
attacks a person with asthma may show no signs at all.
In most cases the physician
can make the diagnosis on the basis of typical symptoms and signs. The typical
rapid changes in airway obstruction can be demonstrated by a fall in
pulmonary function tests spontaneously, after exercise or inhalation of
histamine, and subsequent improvement with an inhaled bronchodilator
medication. Many people with asthma have allergies; positive allergy tests
support a diagnosis of asthma and may help in identifying avoidable
triggers. Other tests (for example chest X-ray or chest CT scan) may be
required to exclude other lung disease.
of exposed sensory nerves e.g. C-fibers is now thought to cause initial
of mast cells by allergens causing release of large amounts of histamine
of bronchial mucosa (the lining of the airway) by lymphocytes
(oedema) of bronchial mucosa
of smooth muscle of bronchioles
(distortion) of the airway
The fundamental problem seems
to be immunological: young children in the early stages of asthma show
signs of excessive inflammation in their airways.
Epidemiology gives clues to
the pathogenesis: the incidence of asthma seems to be increasing worldwide;
asthma is more common in more affluent countries, and more common in higher
socioeconomic groups within countries.
One theory is that it is a
disease of hygiene. In nature, babies are exposed to bacteria soon after
birth, "switching on" the lymphocyte cells of the immune system
which deal with bacterial infection. If this stimulus is insufficient, then
asthma and other allergic diseases may develop. This "Hygiene
Hypothesis" may explain the increase in asthma in affluent populations.
The lymphocytes and eosinophil cells which protect us against worms are the
same cells responsible for the allergic reaction. In the Western world
these parasites are now rarely encountered but the immune response remains
and is triggered in some individuals by certain allergens.
A third theory blames the
rise on asthma on air pollution. While it is well known that substantial exposures
to certain industrial chemicals can cause acute episodes of asthma, it has
not been proven that the same is responsible for the development of asthma.
In Western Europe, most atmospheric pollutants have fallen significantly in
the last forty years while the prevalence of asthma has risen.
Typical triggers include:
allergens such as house dust mite and cockroach, grass pollen, mould spores
and pet epithelial cells.
& similar medications
Episodes of wheeze and
shortness of breath generally respond to inhaled bronchodilators which work
by relaxing the smooth muscle in the walls of the bronchi (airways). More
severe episodes may need short courses of inhaled, oral, or intravenous
steroids which suppress inflammation and reduce the swelling of the lining
of the airway.
Broncho-dilators (usually inhaled)
beta2-adrenoceptor agonists and Antimus carinics are being used today.
Older treatments which have a less selective effect on adrenergic receptors
are inhaled. Epinephrine and Ephedrine tablets; unlike other treatments
both are available over the counter in the US.
Triggers such as pets and
aspirin should be identified and managed. People with asthma who are having
symptoms most days will usually benefit from regular preventive medication.
The inhaled steroids are the most effective preventive medication.