哮喘-Asthma

This leaflet gives a general overview of asthma. There are other leaflets in this series called 'Inhalers for Asthma', 'Peak Flow Meters' and 'Asthma - a Picture Summary'.

What is asthma and who does it affect?

Asthma is a condition that affects the airways (bronchi) of the lungs. from time to time the airways constrict (become narrow) in people who have asthma. This causes the typical symptoms. The extent of the narrowing, and how long each episode lasts, can vary greatly.

Asthma can start at any age, but it most commonly starts in childhood. At least 1 in 10 children, and 1 in 20 adults, have asthma. Asthma runs in some families, but many people with asthma have no other family members affected.

The common symptoms are cough and wheeze. You may also become breathless, and develop a feeling of chest tightness. Symptoms can range from mild to severe between different people, and at different times in the same person. Each episode of symptoms may last just an hour or so, or persist for days or weeks unless treated.

What are the typical symptoms if you have mild (untreated) asthma?
You tend to develop mild symptoms from time to time. For example, you may develop a mild wheeze and a cough if you have: a cold, a chest infection, in the hay fever season, or when you exercise. For most of the time you have no symptoms. A child with mild asthma may have an irritating cough each night, but is often fine during the day.

What are the typical symptoms if you have moderate (untreated) asthma?
Without treatment: you typically have episodes of wheezing and coughing from time to time. Sometimes you become breathless. You may have spells, sometimes long spells, without symptoms. However, you tend to be wheezy for some of the time on most days. Symptoms are typically worse at night, or first thing in the morning. You may wake up some nights coughing or with a tight chest. Young children may not have typical symptoms. It may be difficult to tell the difference between asthma and recurring viral chest infections in young children.

What are the typical symptoms of a severe attack of asthma?
You become very wheezy, have a 'tight' chest, and have difficulty in breathing. You may find it difficult to talk because you are so breathless. Severe symptoms may develop from time to time if you normally have moderate symptoms. Occasionally, severe symptoms develop 'out of the blue' in some people who normally have just mild symptoms.

What causes asthma?

Asthma is caused by inflammation in the airways. It is not known why the inflammation occurs. The inflammation irritates the muscles around the airways, and causes them to squeeze (constrict). This causes narrowing of the airways. It is then more difficult for air to get in and out of the lungs. This leads to wheezing and breathlessness. The inflammation also causes the lining of the airways to make extra mucus which causes cough and further obstruction to airflow.醫(yī)學(xué) 全在.線提供www.med126.com

The following diagram aims to illustrate how an episode of asthma develops.

What can make asthma symptoms worse?

Asthma symptoms may flare up from time to time. There is often no apparent reason why symptoms flare up. However, some people find that symptoms are triggered, or made worse, in certain situations. It may be possible to avoid certain triggers which may help to reduce symptoms. Things that may trigger asthma symptoms include the following.

• Infections. Particularly colds, coughs, and chest infections.
• Pollens and moulds. The hay fever season is a common time for asthma to get worse.
• Exercise. However, sport and exercise are good for you if you have asthma. If necessary, you can use an inhaler before exercise to prevent symptoms from developing.
• Certain drugs. For example, about 1 in 50 people with asthma are allergic to aspirin which can trigger symptoms. Other drugs that may cause asthma symptoms include: anti-inflammatory painkillers, and beta-blockers such as propranolol, atenolol, or timolol. This includes beta-blocker eye-drops used to treat glaucoma.
• Smoking and cigarette fumes. If you smoke and have asthma, you should make every effort to stop. See a practice nurse for help if you find it difficult. 'Passive' smoking can make asthma worse too. All children deserve to live in a smoke-free home, in particular children with asthma.
• Other fumes and chemicals. For example, fumes from paints, solvents and pollution. The increase in air pollution may be a reason why asthma is becoming more common.
• Emotion. Asthma is not due to 'nerves', but such things as stress, emotional upset, or laughing may trigger symptoms.
• Allergies to animals. Such as pet cats, dogs, and horses. Animals do not trigger symptoms in most cases, but some people notice that their symptoms become worse when close to certain animals.
• House dust mite. This is a tiny creature that lives in mattresses and other fabrics around the home. If you are allergic to it, it may make symptoms worse. It is impossible to get rid of house dust mite completely. To greatly reduce their number takes a lot of time and effort and involves: using special mattress covers, removing carpets, removing or treating soft toys, etc. However, if symptoms are difficult to control with treatment, and you are confirmed to be allergic to house dust mite, then it may be worth considering trying to reduce their number. See separate leaflet called 'Allergy to House Dust Mite and Pets'.
• Certain foods. This is uncommon, and food is not thought to be a trigger in most cases.

Some people only develop symptoms when exposed to a certain 'trigger'. Two examples are:

• Occupational asthma. Some people only develop symptoms when exposed to specific substances at work. They have no symptoms at other times.
• Exercise-induced asthma. As mentioned above, exercise can make symptoms worse for many people with asthma. But, some people only develop symptoms when they exercise, and are fine the rest of the time.

How is asthma diagnosed?

Sometimes symptoms are typical, and the diagnosis is easily made by a doctor. If there is doubt then some simple tests may be arranged. A peak flow meter is commonly used to help confirm that symptoms are due to asthma (see below). Sometimes a test called spirometry may be done to confirm the diagnosis. This involves breathing into a machine that measures the rate and volume of airflow in and out of your lungs.

What is the the peak flow meter?

This is a small device that you blow into. A doctor or nurse will show you how. It measures the speed of air that you can blow out of your lungs. No matter how strong you are, if your airways are narrowed, your peak flow reading will be lower than expected for your age, size, and sex. If you have untreated asthma, then you will normally have low and variable peak flow readings. Also, peak flow readings in the morning are usually lower than the evening if you have asthma.

You may be asked to keep a diary over two weeks or so of peak flow readings. Asthma is usually confirmed if you have low and variable peak flow readings over several days. Peak flow readings improve when the narrowed airways are opened up with treatment. Regular peak flow readings can be used to help assess how well treatment is working.

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