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Causes Of Asthma
Asthma attacks are caused by airway hyper receptiveness. The most common
causes of an asthma attack are very small lightweight particles transported
through the air and inhaled into the lungs.
When they enter the airways,
these particles, which are known as environmental triggers, cause an inflammatory
reaction in the airway walls, which results in asthma attack.
Allergens
For some people environmental triggers are allergens. These
are natural substances, such as plant pollen and mould spores, animal
dander (tiny pieces of animal hair and skin), and faecal material from
dust mites and cockroaches.
Allergens produce an inflated response of
the immune system in which a specific antibody immunoglobulin E, initiates
an inflammatory response. These same allergens usually cause little
or no response in non-allergic people.
The allergens involved in asthma
are similar to those in rhinitis. The particle sizes of pollens (>20
microns) mean they are more likely to cause conjunctivitis, rhinitis
and pharyngitis as well as asthma. Allergens from faecal particles of
the house-dust mite are the most important extrinsic cause of asthma
worldwide.
Chemical Irritants
Chemical irritants trigger an inflammatory response differently to allergen-triggered
asthma.
Some people are sensitive to common chemical irritants, such as perfume,
hairspray, make-up, and household cleaners.
Other chemical irritants
include industrial chemicals and plastics, as well as many forms of
air pollution, such as exposure to high levels of ozone, car exhaust, wood
smoke, and sulphur dioxide.
Physiological Triggers
Aggravation from within the body is known as physiological
triggers and includes exercise and infections, such as the common cold.
Sometimes eating certain types of food can cause an asthma attack.
Chemicals
found in food or drugs such as aspirin and ibuprofen can be especially
problematic for many asthma sufferers. Emotions, such as expressions
of grief, shouting, or laughing, can also provoke rapid inhalation of
oxygen causing the airways to narrow which trigger an attack. Many asthmatics
are especially responsive to physical exercise in cold weather.
Causes and triggers of asthma.
Those people who readily develop antibodies of IgE class against
common materials present in the environment can also develop asthma.
Such antibodies are present in 30-40% of the western population, and
there is a link between serum IgE levels and both the prevalence of
asthma and airway responsiveness to histamine or methacholine.
Genetic
and environmental factors affect serum IgE levels and may turn out to
play a key role in the development of asthma.
Early childhood
exposure to allergens and maternal smoking can also cause IgE production.
It has been suggested growing up in a relatively clean environment can
predispose towards an IgE response to allergens. On the other hand,
growing up in a dirtier environment may allow the immune system to avoid
developing allergic responses!
Occupational sensitizers
Over 200 materials encountered in the workplace are recognized as giving
rise to occupational asthma. These are usually recognized as occupational
diseases in the western world.
Asthma sufferers in insurable employment
who can prove their workplace contributed to their condition are eligible
for statutory compensation provided they apply within 10 years of leaving
the occupation in which the asthma developed (UK).
NB. The risk of developing occupational asthma increases in smokers.
The proportion of workers developing occupational asthma depends on their exposure, so the correct enclosure of industrial processes and appropriate ventilation can greatly reduce the risk of contracting Asthma.
Non-specific factors
Characteristic feature of bronchial hyper reactivity in
asthmatics mean as well as reacting to specific antigens their airways
will also respond to a wide variety of non-specific stimuli.
Cold air and exercise
Many asthmatics may experience an attack of wheezing after
they have completed prolonged or non-stop exercise especially in a
cold environment. The attack doesn't occur during the middle of their
exercise period but towards the end. The inhalation of cold, dry air
can also cause an asthmatic attack.
Contact with cigarette smoke, car exhaust fumes, strong perfumes or high concentrations of dust in the atmosphere can be strong factors in causing an asthmatic attack.
Epidemics
Major epidemics of asthma have been recorded when large amounts
of allergens have been released into the air, (e.g. there was a soy bean
epidemic in Barcelona.)
Further insignificant epidemics of asthma have
occurred during periods of heavy atmospheric contamination in industrialized
areas, which is caused by the presence of high concentrations of sulphur
dioxide, ozone, and nitrogen dioxide in the air.
Certain foods such as wine can trigger an asthma attack.
Drugs Used with Asthma
Non-steroid anti-inflammatory drugs (NSAIDs). NSAIDs, chiefly
aspirin, have a major role in the development and precipitation of attacks
in approximately 5% of people with asthma.
Immediate asthma
This is the most common response. An attack begins within minutes
of contact with the allergen, reaches its maximum in 15-20 minutes and
subsides after 1 hour.
Late-phase reactions
Following an instantaneous reaction many asthmatics may develop
more prolonged and sustained attacks that respond inadequately to the
inhalation of bronchodilator drugs.
Dual asthmatic response
This is a combination of an early reaction followed by a late
reaction.
D evelopment of a late-phase response is associated with increases in underlying level of airway hyper reactivity that individuals can show with systematic episodes of asthma on subsequent days
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