Asthma Health Dictionary

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 drugs called 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.

Asthma is a common disorder of breathing characterised by widespread narrowing of smaller airways within the lung. In the UK the prevalence among children in the 5–12 age group is around 10 per cent, with up to twice the number of boys affected as girls. Among adults, however, the sex incidence becomes about equal. The main symptom is shortness of breath. A major feature of asthma is the reversibility of the airway-narrowing and, consequently, of the breathlessness. This variability in the obstruction may occur spontaneously or in response to treatment.

Cause Asthma runs in families, so that parents with asthma have a strong risk of having children with asthma, or with other atopic (see ATOPY) illnesses such as HAY FEVER or eczema (see DERMATITIS). There is therefore a great deal of interest in the genetic basis of the condition. Several GENES seem to be associated with the condition of atopy, in which subjects have a predisposition to form ANTIBODIES of the IgE class against allergens (see ALLERGEN) they encounter – especially inhaled allergens.

The allergic response in the lining of the airway leads to an in?ammatory reaction. Many cells are involved in this in?ammatory process, including lymphocytes, eosinophils, neutrophils and mast cells. The cells are attracted and controlled by a complex system of in?ammatory mediators. The in?amed airway-wall produced in this process is then sensitive to further allergic stimuli or to non-speci?c challenges such as dust, smoke or drying from the increased respiration during exercise. Recognition of this in?ammation has concentrated attention on anti-in?ammatory aspects of treatment.

Continued in?ammation with poor control of asthma can result in permanent damage to the airway-wall such that reversibility is reduced and airway-narrowing becomes permanent. Appropriate anti-in?ammatory therapy may help to prevent this damage.

Many allergens can be important triggers of asthma. House-dust mite, grass pollen and animal dander are the commonest problems. Occupational factors such as grain dusts, hard-metals fumes and chemicals in the plastic and paint industry are important in some adults. Viral infections are another common trigger, especially in young children.

The prevalence of asthma appears to be on the increase in most countries. Several factors have been linked to this increase; most important may be the vulnerability of the immature immune system (see IMMUNITY) in infants. High exposure to allergens such as house-dust mite early in life may prime the immune system, while reduced exposure to common viral infections may delay the maturation of the immune system. In addition, maternal smoking in pregnancy and infancy increases the risk.

Clinical course The major symptoms of asthma are breathlessness and cough. Occasionally cough may be the only symptom, especially in children, where night-time cough may be mistaken for recurrent infection and treated inappropriately with antibiotics.

The onset of asthma is usually in childhood, but it may begin at any age. In childhood, boys are affected more often than girls but by adulthood the sex incidence is equal. Children who have mild asthma are more likely to grow out of the condition as they go through their teenaged years, although symptoms may recur later.

The degree of airway-narrowing, and its change with time and treatment, can be monitored by measuring the peak expiratory ?ow with a simple monitor at home – a peak-?ow meter. The typical pattern shows the peak ?ow to be lowest in the early morning and this ‘morning dipping’ is often associated with disturbance of sleep.

Acute exacerbations of asthma may be provoked by infections or allergic stimuli. If they do not respond quickly and fully to medication, expert help should be sought urgently since oxygen and higher doses of drugs will be necessary to control the attack. In a severe attack the breathing rate and the pulse rate rise and the chest sounds wheezy. The peak-?ow rate of air into the lungs falls. Patients may be unable to talk in full sentences without catching their breath, and the reduced oxygen in the blood in very severe attacks may produce the blue colour of CYANOSIS in the lips and tongue. Such acute attacks can be very frightening for the patient and family.

Some cases of chronic asthma are included in the internationally agreed description CHRONIC OBSTRUCTIVE PULMONARY DISEASE (COPD) – a chronic, slowly progressive disorder characterised by obstruction of the air?ow persisting over several months.

Treatment The ?rst important consideration in the treatment of asthma is avoidance of precipitating factors. When this is a speci?c animal or occupational exposure, this may be possible; it is however more di?cult for house-dust mite or pollens. Exercise-induced asthma should be treated adequately rather than avoiding exercise.

Desensitisation injections using small quantities of speci?c allergens are used widely in some countries, but rarely in the UK as they are considered to have limited value since most asthma is precipitated by many stimuli and controlled adequately with simple treatment.

There are two groups of main drugs for the treatment of asthma. The ?rst are the bronchodilators which relax the smooth muscle in the wall of the airways, increase their diameter and relieve breathlessness. The most useful agents are the beta adrenergic agonists (see ADRENERGIC RECEPTORS) such as salbutamol and terbutaline. They are best given by inhalation into the airways since this reduces the general side-effects from oral use. These drugs are usually given to reverse airway-narrowing or to prevent its onset on exercise. However, longer-acting inhaled beta agonists such as salmeterol and formoterol or the theophyllines given in tablet form can be used regularly as prevention. The beta agonists can cause TREMOR and PALPITATION in some patients.

The second group of drugs are the antiin?ammatory agents that act to reduce in?ammation of the airway. The main agents in this group are the CORTICOSTEROIDS. They must be taken regularly, even when symptoms are absent. Given by inhalation they have few side-effects. In acute attacks, short courses of oral steroids are used; in very severe disease regular oral steroids may be needed. Other drugs have a role in suppressing in?ammation: sodium cromoglycate has been available for some years and is generally less e?ective than inhaled steroids. Newer agents directed at speci?c steps in the in?ammatory pathway, such as leukotriene receptor-antagonists, are alternative agents.

Treatment guidelines have been produced by various national and international bodies, such as the British Thoracic Society. Most have set out treatment in steps according to severity, with objectives for asthma control based on symptoms and peak ?ow. Patients should have a management plan that sets out their regular treatment and their appropriate response to changes in their condition.

Advice and support for research into asthma is provided by the National Asthma Campaign.

See www.brit-thoracic.org.uk

Prognosis Asthma is diagnosed in 15–20 per cent of all pre-school children in the developed world. Yet by the age of 15 it is estimated that fewer than 5 per cent still have symptoms. A study in 2003 reported on a follow-up of persons born in 1972–3 who developed asthma and still had problems at the age of nine. By the time these persons were aged 26, 27 per cent were still having problems; around half of that number had never been free from the illness and the other half had apparently lost it for a few years but it had returned.

n. the condition of subjects with widespread narrowing of the bronchial airways, which changes in severity over short periods of time (either spontaneously or under treatment) and leads to cough, wheezing, and difficulty in breathing. Bronchial asthma may be precipitated by exposure to one or more of a wide range of stimuli, including *allergens, drugs (such as aspirin and other NSAIDs and beta blockers), exertion, emotion, infections, and air pollution. The onset of asthma is usually early in life and in atopic subjects (see atopy) may be accompanied by other manifestations of hypersensitivity, such as hay fever and dermatitis; however, the onset may be delayed into adulthood or even middle or old age. Treatment is with *bronchodilators, with or without corticosteroids, usually administered via aerosol or dry-powder inhalers, or – if the condition is more severe – via a nebulizer. Oral corticosteroids are reserved for those patients who fail to respond adequately to these measures. Severe asthmatic attacks may need large doses of oral corticosteroids (see status asthmaticus). Selection of treatment for individual cases is made using stepped guidelines issued by respiratory organizations, e.g. the British and American Thoracic Societies and the European Respiratory Society. A new group of drug treatments, using *monoclonal antibodies to target components in the allergic response, have recently become available (see omalizumab). Avoidance of known allergens, especially the house dust mite, allergens arising from domestic pets, and food additives, will help to reduce the frequency of attacks, as will the discouragement of smoking.

Cardiac asthma occurs in left ventricular heart failure and must be distinguished from bronchial asthma, as the treatment is quite different. —asthmatic adj.