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| Asthma brought on by exercise |
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Written by Dr Nicola Wilson, honorary consultant paediatrician
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Asthma brought on by exercise (asthma
on exercise) happens to almost all people with asthma, or at least it would if
their treatment was reduced or stopped.
If you have never experienced asthma when exercising it may be
wise to reconsider the diagnosis. In some people it is the only symptom of
their asthma.
Since we all exercise, it is a potential problem for all those
with asthma. However, in the vast majority it can be readily controlled with
medication and other measures.
What are the symptoms of asthma on exercise?
The symptoms of asthma on exercise, either in combination or
alone, include:
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cough, but asthma is not the only cause.
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chest tightness and difficulty in breathing
(wheezing).
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shortness of breath (this is different from being unfit because
it gets worse, not better, after exercise has finished).
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symptoms usually begin after exercise has stopped, and are at
their worst about five minutes afterwards.
-
more severe attacks may start during exercise and as a result
the activity has to stop.
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wheezing or chest tightness gradually lessens over the next
10-30 minutes if the asthma attack is untreated. Recovery can take longer if
the attack is very severe.
What causes asthma on exercise?
Nobody really knows the exact reason why asthma is brought on by
exercise. The mechanism may be quite complicated and involve sensory nerves and
the redistribution of blood flow throughout the lung. The process is thought to
include the events outlined below.
When we exercise, we breathe faster and more heavily and this
leads to the following situation:
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the lining of the airways dries out, concentrating the contents
of the cells in that area. This is called increased osmotic load.
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the airways cool rapidly because of evaporative heat
loss.
In untreated, or under-treated, asthma the lining of the airway
is inflamed. The drying and perhaps the cooling of the airways act as physical
triggers to cause cells in the inflamed airways to release 'constrictor'
chemicals, which in turn cause muscles in the airways to contract and narrow,
and give rise to the typical symptoms of asthma.
Evidence for the mechanism of asthma on exercise
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Asthma on exercise can be mimicked by voluntarily increasing
the breathing rate.
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Breathing warm, humid air reduces or prevents asthma on
exercise. The reason seems to be that that there is less dryness and cooling of
the airway lining. Therefore, there is less release of constrictor chemical and
less narrowing of the airways, which leads to reduced symptoms of asthma on
exercise.
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Breathing cold, dry air increases asthma on exercise. The
dryness and increased cooling factors lead to greater release of constrictor
chemical and more narrowing of the airways resulting in the typical symptoms of
asthma.
Who gets asthma on exercise?
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Nearly everyone with under-treated asthma who
exercises.
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A few people with severe asthma, despite receiving the best
treatment.
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Children are particularly affected as they tend to run around
more than adults.
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When tested, 2.5-30 per cent of school children have evidence
of asthma on exercise 1,2. The actual number depends
on the geographical locality.
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When tested 12-15 per cent of unselected athletes reported
asthma on exercise3.
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At the 1996 Olympic games 20 per cent of athletes reported
asthma on exercise4.
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Reduced lung function may occur after exercise in some people
with hay fever (without actual diagnosed asthma). This can represent
unrecognised asthma on exercise. It occurs because the airways of people with
hay fever are often inflamed and so will respond to the effects of airway
drying5.
Severity of symptoms
The severity of the symptoms depends on:
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an individual's response (some people are more sensitive than
others). This may vary according to the situation (eg worse during colds or
when suffering from hay fever).
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how cold and dry the air is. The colder and dryer the air, the
greater the changes in the lining of the airways and the larger the stimulus
for release of constrictor chemical. This results in more severe
symptoms.
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if the exercise is continuous (eg cross-country running), in
which case the symptoms may be more severe.
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if the exercise is intermittent (eg tennis), when the problem
may be less troublesome and symptoms less severe.
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how strenuous the exercise is. The more energetic the exercise,
the greater the need to breathe heavily and the greater the degree of airway
drying and cooling, which can result in more severe symptoms.
So asthma on exercise can occur in:
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people who are very sensitive to airway drying, even after
minimal exercise.
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those who are not very sensitive to airway drying, but who
exercise very vigorously, such as amateur or professional athletes.
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people somewhere in between the two.
Can I exercise if I get asthma on exercise?
Yes! There are many athletes who have asthma on exercise and
there are many steps you can take to reduce or avoid it.
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There are effective medications such as your reliever inhaler,
eg salbutamol, terbutaline, or your sodium cromoglicate inhaler, which can be
used immediately before exercise.
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Recommended medications, such as salbutamol, terbutaline and
sodium cromoglicate, are allowed by sports councils (check with your doctor if
you take an unusual preparation, as some contain substances, such as ephedrine,
that are not allowed).
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Those with troublesome asthma may have to choose a type of
exercise that suits them, such as swimming or bowls, or avoid too much exercise
at the times of the year when their asthma is a particular problem.
It is important to remember that in some people under-treated
asthma on exercise can lead to a dangerous attack in certain situations, such
as when there are high levels of pollution in the atmosphere or very cold
days.
How can I use my medication to avoid asthma on
exercise?
There are two ways in which medication can be used to prevent
asthma on exercise:
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short-term protection
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long-term protection.
Short-term protection
This lasts three to four hours and the inhaler is used before
exercise. In general, if you need to use your reliever inhaler less than once a
day, you don't need to use a preventer as well. If you use your reliever
more than this you should also be using a preventer. Medications that can
provide short-term protection include:
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short-acting reliever inhalers, which open the airways and
are often blue, such as salbutamol (eg Ventolin) and terbutaline (eg Bricanyl). These stop airway muscles
contracting when the constrictor chemical is released.
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instead of a short-acting reliever, a long-acting one, such
as salmeterol (Serevent)
or formoterol (eg Foradil or
Oxis) taken morning and night,
will give 24-hour cover. These should only be used without a preventer in
special circumstances (for example, in a child with mild asthma on a day with a
school sports lesson, when access to inhalers at school is a
problem).
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sodium cromoglicate (eg Intal) or nedocromil sodium (Tilade) are less commonly used, but
may be useful in amateur and professional athletes.
Long-term protection
These preventers work by reducing the inflammation in the
airways that cause asthma. Overall improvement in asthma occurs, which includes
asthma on exercise. To work, the preventers have to be taken every day for long
periods of time. They do not work as a single dose before exercise and the
benefit may not be noticed for at least a week. Medications that can provide
long-term protection include:
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inhaled steroids, such as beclometasone (eg Becotide),
fluticasone (Flixotide) and budesonide (eg Pulmicort)
through an inhaler.
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leukotriene receptor antagonist tablets, such as zafirlukast (Accolate)
or montelukast (Singulair), are fairly new. It is not known how many people will benefit
from them, or for how long you need to take the tablets before they
work.
Other things I can do to reduce or avoid asthma on
exercise
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Avoid exercising outside on cold and frosty days, as cold air
holds less water vapour, and drying and cooling of your airways acts as a
stimulus for release of constrictor chemical.
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Make sure you breathe through your nose because the nose warms
and humidifies the air, which is then less of a stimulus to constrictor
mediator release.
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Before starting exercise, warm-up first, with short bursts of
exercise because this may reduce the asthma that follows on more strenuous and
prolonged exercise. The explanation for this is not quite clear, but two
factors may play a part. Firstly, small amounts of exercise may actually
improve your lung function (look at the graph, which shows an improvement in
lung function during the early part of exercise). Secondly, even though the
warm-up does not cause asthma itself, it may reduce the ability of your airway
cells to release the constrictor chemical that causes the symptoms of
asthma.
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If running is a problem, try swimming because the humid air in
the swimming bath may cause less drying of your airways. Try an intermittent
sport (eg tennis, bowls) or exercise indoors on cold days (eg gymnastics,
aerobics, badminton).
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Choose sprinting rather than cross-country running, because you
can run short distances at speed taking only a few breaths, so there is less
drying and cooling of your airways.
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Avoid exercising on days with high pollen counts if you are
sensitive to pollen, or days with high pollution, because you may inhale more
pollutants/pollen with the increased breathing needed during exercise. These
generally aggravate asthma in people who are susceptible.
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Keep fit because, as your fitness increases, you will breathe
less heavily for a given amount of exercise and so reduce the stimulus for
asthma.
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Most importantly, keep your asthma under control.
Specific problems with exercise and asthma
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Exercise anaphylaxis. This is a rare condition in which the
combination of exercise and allergy to a particular food eaten immediately
beforehand causes collapse and difficulty breathing (similar to the severe
allergic reaction to peanuts experienced by some people).
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Exercise associated with laughter and excitement (eg a birthday
party, visits by friends and relatives) can be troublesome for some children.
This should be anticipated and a reliever inhaler given beforehand.
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Occasionally, people with severe asthma experience asthma on
exercise in spite of high-dose medication. In these cases, gentler, less
provoking activities such as bowls should be chosen.
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References
Austin JB, Russell G, Adam MG, Mackintosh D, Kelsey S,
Peck DF. Prevalence of asthma and wheeze in the Highlands of Scotland. Arch Dis
Child 1994; 71: 211-216.
Jones CO, Quereshi S, Rona RJ, Chinn S. Exercise-induced
bronchoconstriction by ethnicity and presence of asthma in British 9 year olds.
Thorax 1996; 51: 1134-1136.
Weiler JM. Exercise-induced asthma: a practical guide to
definitions, diagnosis, prevalence and treatment. Allergy Asthma Proc 1996; 17:
315-325.
Weiler JM, Layton T, Hunt M. Asthma in United States
Olympic athletes who participated in the 1996 Summer Games. J Allergy Clin
Immunol 1998; 102: 722-726.
Corren J. The relationship between allergic rhinitis and
bronchial asthma. Curr Opin Pulm Med 1999; 5: 35-37.
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Last updated 01.08.2005
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