Allergic asthma is dependent on IgE response controlled by T and B
lymphocytes and activated by the interaction of antigen with mast cells-bound
IgE molecule. Most of the allergens are airborne and to induce a state of
sensitivity, they must be reasonably abundant for considerable period of time.
Allergic asthma is frequently seasonal and it is most after observed in
children and young adults. A non-seasonal form may result from allergy to
feathers, animal dander, dust mites, molds and other antigens that are present
continuously in the environment.
2. Pharmacological stimuli
The drugs most commonly associated with the induction of acute
episodes of asthma are aspirin, colouring agents – tartazine, β- adregenic
antagonists, sulfating agent.
Aspirin – sensitive syndrome affects adults through seen in childhood.
The problem usually begins with perennial vasomotor rhinitis that is followed
by a hyper plastic rhino sinusitis with nasal polyps, progressing to asthma.
Indomethacin, fenoprofen, naprocen, zonepirae sodium, ibuprofen, mefanamic
acid and phenylbutazone are particularly important.
β- Adrenergic antagonist regularly obstructs the airway in asthmatics. In
fact, the local use of β- blockers in the eye for the treatment of glaucoma has
been associated with worsening asthma.
Sulfating agents can produce acute airway obstruction in sensitized
individuals. Exposure usually follows ingestion of food and beverages
containing these compounds. e.g. – salads, fresh fruit, potatoes, shell fish &
3. Environment and Air pollution
Environmental causes of asthma are usually related to climatic
conditions that promote the concentration of atmospheric pollutants and
antigens. These conditions tend to develop heavily industrial or densely
populated urban areas and frequently associated with thermal inversion or other
situation that cause stagnant air masses. The air pollutants known to have this
effect are ozone, nitrogen dioxide & sulphur dioxide.
4. Occupational factors
Occupation – related asthma is a significant health problem and acute
and chronic airway obstructions have been reported to follow exposure to a
large number of compounds used in many types of industrial process.
Broncho constriction can result from working with or being exposed to
metal salts, wood and vegetable dust, husk of grains, flour, castor bean, gum
acacia, karay gum, tragacanth, pharmaceutical agents e.g. antibiotics,
piperazine and cimetidine, industrial chemicals and plastics, biological
enzymes, laundry detergents and pancreatic enzymes, animal & insect dusts,
serum and secretions.
There seems to be three underlying mechanisms
1. In some cases, the offending agent results in formation of significant
2. Substances cause direct liberations of broncho constrictor substances.
3. Substances cause direct or reflex stimulation of the airway of latent of
Respiratory infections are the most common of the stimuli that evoke
exacerbations of asthma. In young children, the most important infectious
agents are respiratory syntical virus and para influenza virus. In older children
and adults rhino virus and influenza virus predominate as pathogens.
Streptococcus pneumoniae, H.influenza and viruses are responsible for
Simple colonization of the tracheo bronchial tree is insufficient to evoke
acute attacks & attack of asthma occurs only when the symptoms of an ongoing
respiratory tract infection are having been present. The mechanism by which
viruses induce exacerbations of asthma may be related to the production of T
lymphocyte derived cytokines that potentiate the infiltration of inflammatory
cell into already susceptible airways.
Exercise is one of the most common precipitating factors in acute
episodes of asthma. Exercise probably invokes broncho spasm to some extent
in every asthmatic patient, and in some it is the only trigger that produces
symptoms. The mechanisms, by which exercise produce obstruction, may be
related to a thermally produced hyperthermia and engorgement of the
microvasculature of the bronchial wall and doesn’t appear to involve smooth
7. Emotional Stress
Psychological factors can interact with the asthmatic diasthesis to
worsen or ameliorate disease process. Changes in airway caliber seem to be
mediated through modification of nasal efferent activity, but endorphins also
may play a role.
8. Food and Drink
Atopic asthmatics may occasionally notice that their symptoms are
provoked by certain foods or drinks and it is worth enquiring of all asthmatic
patients whether they have notices such as association.
The food most frequently suspected the milk, eggs, fish, cereals, nuts
and chocolates. Preservatives such as benzoates, sodium nitrite, and sodium
metabisulphite, anti oxidants, dyes such as tartarzine, flavorings may be found
in many food and may provoke asthma. Red wines contain a number of
congeners which give them their distinctive flavors but which also may
provoke attacks of asthma.
Smokers appear to be at greater risk of developing asthma and have a
higher prevalence of hyper-reactivity. Children of smokers also seem to have
an increased risk of developing wheeze.