Asthma
Asthma - sometimes called bronchial asthma - is obstruction of the airways which, at least in the early stages, is reversible. There are three components to the obstruction: inflammatory cells causing swelling of the mucous lining, increased mucus production, and constriction of the bronchial smooth muscle. The characteristic features are cough, chest tightness with shortness of breath, and wheeze. Symptoms may be worse at night, or precipitated by exercise or exposure to cold air, emotion or stress. By far the commonest cause is allergy to some environmental factor such as house dust mite or animal fur following sensitisation of inflammatory cells, called mast cells, to the presence of the allergen (the substance we’re allergic to). Allergy means altered energy, and it is an exaggeration of a normal response. Asthma in infancy and childhood is increasing in incidence in the Western world, as are allergies overall, for reasons that are obscure. Patients with sensitised mast cells are said to be atopic, and there may be other manifestations of allergy such as eczema or rhinitis. It may not be possible to avoid the agent responsible, though if it is we should do so - the family cat might have to go. Short-term measures to reduce constriction using inhalers which act to relax the bronchial smooth muscle are useful during acute attacks, but measures to reduce the inflammation are more effective in preventing deterioration.
The obstruction of the airways causes difficulty in breathing out. We can measure the effectiveness of treatment by measuring how quickly we breathe out using a peak flow meter. This can alert us to deterioration in the condition which may necessitate changes in treatment. Patients who suffer exacerbation of their asthma during infections, for example, may need to use steroids.
Aspirin induced asthma occurs in people who have a different metabolic pathway involving a chemical called arachidonic acid. Aspirin blocks an enzyme in this pathway and, rather than reducing inflammation, in these patients induces an inflammatory reaction involving leucotrienes which precipitates an asthma attack. They suffer similar attacks every time they are exposed to aspirin, or other anti-inflammatory drugs of a similar nature.
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