asthma

asthma - A lung disease in which there is intermittent narrowing of the bronchi (airways), causing shortness of breath, wheezing, and cough. The illness often starts in childhood but can develop at any age. At least 1 child in 7 suffers from asthma, and the number affected has increased dramatically in recent years. Childhood asthma may be outgrown in about half of all cases.

During an asthma attack, the muscle in the walls of the airways contracts, causing narrowing. The linings of the airways also become swollen and inflamed, producing excess mucus that can block the smaller airways. In some people, an allergic response triggers the airway changes. This allergic type of asthma tends to occur in childhood and may develop in association with eczema or certain other allergic conditions such as hay fever (see rhinitis, allergic).

Susceptibility to these conditions frequently runs in families and may be inherited. Some substances, called allergens, are known to trigger attacks of allergic asthma. They include pollen, house-dust mites, mould, and dander and saliva from furry animals such as cats and dogs. Rarely, certain foods, such as milk, eggs, nuts, and wheat, provoke an allergic asthmatic reaction. Some people with asthma are sensitive to aspirin, and taking it may trigger an attack.

When asthma starts in adulthood, there are usually no identifiable allergic triggers. The 1st attack is sometimes brought on by a respiratory infection. Factors that can provoke attacks in a person with asthma include cold air, exercise, smoke, and occasionally emotional factors such as stress and anxiety. Although industrial pollution and exhaust emission from motor vehicles do not normally cause asthma, they do appear to worsen symptoms in people who already have the disorder.

Pollution in the atmosphere may also trigger asthma in susceptible people. In some cases, a substance that is inhaled regularly in the work environment can cause a previously healthy person to develop asthma. This type is called occupation asthma and is one of the few occupational lung diseases that is still increasing in incidence.

There are currently about 200 substances used in the workplace that are known to trigger symptoms of asthma, including glues, resins, latex, and some chemicals, especially isocyanate chemicals used in spray painting. However, occupational asthma can be difficult to diagnose because a person may be regularly exposed to a particular trigger substance for weeks, months, or even years before the symptoms of asthma begin to appear.

Asthmatic attacks can vary in severity from mild breathlessness to respiratory failure. The main symptoms are wheezing, breathlessness, dry cough, and tightness in the chest. In a severe attack, breathing becomes increasingly difficult, resulting in a low level of oxygen in the blood. This causes cyanosis (bluish discoloration) of the face, particularly the lips. Untreated, such attacks may be fatal.

There is no cure for asthma, but attacks can be prevented to a large extent if a particular allergen can be identified. Treatment involves inhaled bronchodilator drugs (sometimes known as relievers) to relieve symptoms. When symptoms occur frequently, or are severe, inhaled corticosteroids are also prescribed. These drugs are used continuously to prevent attacks by reducing inflammation in the airways and are also known as preventers.

Other drug treatments include sodium cromoglicate and nedocromil sodium, which are useful in preventing exerciseinduced asthma. A new group of drugscalled leukotriene receptor antagonists may reduce the dose of corticosteroid needed to control the condition. Theophylline or the inhaled anticholinergic drug ipratropium may also be used as bronchodilators.

An asthma attack that has not responded to treatment with a bronchodilator needs immediate assessment and treatment in hospital.