The rise and rise of asthma

Key text

What is asthma?

Whenever we take a breath, we take air into our lungs through a complicated system of tubes, called airways. These airways empty the exhaust gases from our lungs and resupply them with oxygen-rich fresh air. Asthma is a condition where the airway walls become inflamed. The airways become narrower than usual and partially blocked, and may eventually become permanently damaged.

Asthma is a long-lasting problem – doctors call it a chronic disease. Sufferers can usually lead relatively normal lives (although they may be a bit breathless and have a frequent cough). Once someone has asthma, symptoms can be set off or made worse by triggers, leading to an asthma attack.

People suffering an attack will have some or all of these symptoms:

• difficulty breathing, or feeling out of breath for no reason;
• wheezing, especially when breathing out;
• tightness in the chest;
• coughing.

During an attack, the airways narrow because the muscles in their walls are squeezing them. This is called bronchoconstriction. In addition, more and thicker mucus is secreted into the airways, and their inner lining becomes inflamed and over-sensitive to any irritants. A severe asthma attack, if not treated in time, can prove fatal.

Causes of asthma

It is hard to know exactly what causes airway inflammation and asthma. Genetic factors play a part. Some people have an underlying predisposition. There is strong evidence that exposure to allergens in early life increases their risk of developing asthma. Asthma is also more likely to occur in someone with relatives who suffer from some form of allergy. Asthma can also be caused by exposure to some occupational sensitisers.

What triggers asthma symptoms?

Once the airways are inflamed, they become twitchy and oversensitive to different triggers, such as:

• allergens;
• polluted air, including cigarette smoke;
• infections of the airways (eg, colds);
• cold air;
• exercise;
• strong emotions.

But it is not always clear what triggers an asthma attack.

Types of asthma

Not all asthma is the same. There are two general types, sometimes called extrinsic (allergic) and intrinsic (non-allergic). About two-thirds of asthmatics suffer from allergic asthma and one-third suffer from non-allergic asthma.

Both types of asthma can be made worse by polluted air, even if it is not a trigger. This is especially true if the air contains sulfur dioxide, nitrogen oxides and ozone. These gases irritate the airways (as do many components in cigarette smoke), worsening an asthmatic’s condition.

Other factors also play a part in asthma. Some studies have suggested that the way we breathe and the depth of our breathing may affect the degree of tightness of the muscles that surround the airways.

Prevention and management

Unfortunately, there is as yet no real cure for asthma. The drugs used to treat it either prevent the occurrence of an attack, or relieve the symptoms of an attack (Box 1: Treatment options). When asthma is controlled by medication, exercise can be beneficial rather than acting as a trigger. Several top athletes are asthmatics.

Incidence in Australia

Asthma has been on the rise in Australia for many years; although the rise seems to have plateaued now. We have the dubious honour of being one of the world’s asthma hot spots. About 10 per cent of Australians have a problem with the disease, and about 20 per cent of children suffer from an asthma attack at some stage. Asthma ranks among the top ten reasons for visiting a doctor.

There are many theories about why the incidence of asthma is so high here. Ideas range from changes in asthma diagnosis (conditions that used to be classified as something else are now diagnosed as asthma) to the occurrence of house dust mites or large quantities of pollen.

Most Australian cities are situated in warm, humid areas – ideal conditions for house dust mites to thrive. The mites are so small that they are invisible to the unaided eye, but they breed in dust, carpets, mattresses and pillows. The mites are harmless, but when their droppings are inhaled they can trigger a reaction that makes some people sneeze and causes asthma in others.

But house dust mites are not the whole story. The rates of asthma around the world do not follow the known extent of dust mite infestations. Asthma rates are lower in less-developed countries and one authority suggests that the reduction in childhood respiratory diseases in our medically efficient world may cause the immune system in the lungs and airways to over-react when exposed to substances that it should tolerate. The 'hygiene hypothesis' suggests that our modern hygienic lifestyles may be contributing to an increased prevalence of asthma. Because children are being exposed to fewer infectious microorganisms, their immune system may develop differently, leading them to over-react to substances like pollen and dust mites.

Australian research into asthma

Throughout Australia, doctors and scientists are studying the causes and treatment of asthma (Box 2: Australian research).

Box 1. Treatment options

Preventers can stop the airways becoming obstructed. They do this by preventing the inner lining from becoming inflamed and from producing too much mucus. These medicines are therefore called anti-inflammatory agents. Most are corticosteroids (or steroids for short). They must be used carefully because they can cause side-effects. Another type of preventer called cromolyn (or disodium cromoglycate) stops the cells lining the airways from reacting to allergens.

Relievers are a different class of drug. They are designed to relieve the symptoms once an attack is underway. They can also be used before exercise to prevent exercise-induced asthma. The majority are called bronchodilators because they dilate the airways. They do this by making the muscles around the airways relax. There are many different types. Most are inhaled so that they reach the airways immediately.

Peak-flow meters

The peak-flow meter is a way of measuring how the airways are performing. If the peak-flow reading is lower than usual, it is a sign that the airways are becoming partly blocked. In this way the asthmatic can monitor whether extra medication or a visit to the doctor is necessary.

Careful and regular use of the prescribed medication is important in asthma. In 2006, 402 Australians died from the disease, but many deaths can be prevented. Of course, an important part of asthma management is to avoid situations that are known to bring on attacks wherever possible. That is the best medicine of all.

Related sites

• Asthma Management Handbook 2002 (National Asthma Council Australia)

• Asthma medications (Kids with asthma, Australia)

Box 2. Australian research

Whilst Australia has one of the highest rates of asthma in the world, Australian researchers are uncovering more about its causes and finding potential new mechanisms with which to treat it. Finding out more about the reasons why allergic (extrinsic) asthmatics react so strongly to their allergic triggers is being studied by several Australian research teams.

One of the great mysteries of the allergic type of asthma – or indeed of any allergic condition – is why the body makes such a fuss over totally harmless airborne particles. We know that what we call allergens are simply materials mistaken for invading microbes or their products. It’s a costly mistake: the entire immune system is put on red alert to counter a non-existent threat, and the result is the gamut of symptoms that sufferers must endure. But why? Grass pollen or mite faeces should not be genuine problems for the human body; after all, the majority of people don’t react to them at all.

Asthma begins in early life

Research stemming from Perth has established that a large proportion of asthma that occurs during the school years and often continues into adulthood is a result from damage to the growing lung and airways when a person is only 2 to 3 years of age. The main culprits are allergies to airborne agents such as dust mites and respiratory viruses. Teams from the Telethon Institute for Child Health Research led by Professors Patrick Holt and Peter Sly and from the University of Western Australia Department of Pediatrics led by Professor Peter Lesouef have recently uncovered some new findings involving the inflammatory pathways that are triggered by such airborne irritants. The team have discovered that “storms” of cytokines – small cell-signaling protein molecules – are created in the airways, cause more pro-inflammatory cells to be released from the bone marrow. This in turn leads to the rapid worsening of symptoms in the airways. Understanding more about this mechanism is going a long way to explaining the annual epidemics of severe asthma that fill paediatric hospital beds around the world during autumn and winter, and is providing exciting new clues for the development of more effective asthma treatments.

Eosinophils respond to allergens in asthmatics

Researchers know that the chief culprit in causing much of the damage in an asthma attack is a fairly rare type of white blood cell called the eosinophil. Eosinophils are designed to be the ‘heavy force’ of the immune system, being equipped to deal with occasional 'big' invaders such as worms. It seems quite bizarre, but in asthmatics these cells are unleashing their strong destructive power onto the patient’s uninfected tissue without any provocation.

So why and how are the eosinophils brought into the airways and lungs by allergens? In 1985, a team in London headed by Professor Colin Sanderson discovered that interleukin (an immune system molecule) was controlling eosinophil production. His team moved to Perth in 1993 and their research has since shown that there are actually two chemical messengers involved in eosinophil control, known now as interleukin-4 (IL-4) and interleukin-5 (IL-5). These signaling molecules are secreted into the bloodstream by other cells of the immune system (T-cells), and can attract eosinophils. Researchers are now continuing to investigate how the release of these interleukins can be blocked, in order to stop the accumulation of eosinophils that may subsequently lead to an asthma attack.

MicroRNA as a new target in asthma

The genomics revolution is increasingly providing many new opportunities for asthma research. For example at the University of Newcastle Professor Paul Foster’s group are attempting to tease apart some of the complex mechanisms that underlie the body’s excessive white blood cell response to inhaled asthma triggers. It has now been revealed that specific receptors on cells of the immune system are important for detecting the molecular patterns of airborne antigens that become trapped in mucous lining the airways, causing T cell responses. Prof Fosters group have shown that purposely setting off these receptors with house dust mite allergen (a major trigger of asthma attacks) causes allergic disease, and that importantly, this process is associated with the expression of a unique subset of small molecules known as microRNAs. They have found that selectively blocking these microRNAs decreases many of the major characteristics of asthma, such as airway inflammation, sensitivity to inhaled irritants, recruitment of eosinophils, and secretion of mucus which can plug the airways during an asthma attack. Their findings point towards targeting microRNA in the airways as an exciting new approach towards developing new anti-inflammatory treatments for allergic asthma.

Smooth muscle cells as active participants as opposed to innocent bystanders in inflammatory processes in the asthmatic airways

At the University of Sydney and the Woolcock Institute of Medical Research Professor Judith Black and colleagues are changing perceptions of the role of the airway smooth muscle –which lines the airway walls and which contracts to bring about the narrowing of the airways, wheeze and shortness of breath which occurs in asthma. Traditionally believed to be one of the main targets of airway inflammation causing the symptoms of asthma, it has been found that the smooth muscle is actively involved in both the generation and regulation of local inflammatory processes in conjunction with its neighbours – the epithelial and inflammatory cells. Evidence is rapidly accumulating that the smooth muscle itself may be innately abnormal. Certainly the amount of smooth muscle in the airways of people with asthma is increased and Professor Black’s team have shown that muscle cells taken from people with asthma multiply in the lab at nearly twice the normal rate. Researchers are hoping that this recently acquired knowledge will help in the development of new asthma treatments.

Prof Judith Black’s team at the University of Sydney are studying the cellular and molecular basis of lung diseases such as asthma. Here PhD student Jade applies stain to sections of human lung tissue. (Image:Woolcock Institute of Medical Research, Sydney. Photography (c) Chris L Jones.

Lipid pathways in allergic airways inflammation

Professor Charles Mackay’s research group at the Garvan Institute of Medical Research in Sydney is also providing new insights into asthma, including the role of lipids – a naturally occurring class of molecules in the body that include fats. They have found that a fatty acid binding protein called aP2 – a molecule already known to be involved in type 2 diabetes and obesity – is present in the lung where it plays a crucial role in controlling inflammation. The aP2 binding protein helps to recruit certain white blood cells into the lungs, and even more aP2 was produced when it was exposed to cytokines often associated with allergies and asthma. Using a mouse model, researchers removed the gene controlling aP2 production, and found that mice without aP2 were subsequently protected from asthma attacks. Blocking aP2 function is now being investigated as a novel approach to treat asthma and other inflammatory lung diseases.

In a further novel twist in the lipid saga, the Mackay group have also used mice to show that the short chain fatty acids produced by the fermentation of dietary fibre by microbes in the intestine may also play a central role in reducing inflammation outside of the gastrointestinal tract, including in asthma. This finding provides a potential mechanism for earlier findings in humans which suggest that control of the microflora via regular feeding of prebiotics or probiotics can in some circumstances protect against airway inflammation, and that maintaining a “normal” gut flora seems to be important in resistance to many inflammatory diseases. Lipid metabolites of this nature may therefore play an unexpectedly important mediator role, and it is hoped that finding out more about the pathways involved may lead to novel therapies in the future for asthma and other diseases.

Related sites

• Asthma CRC Research
• Developments in asthma research (the Asthma Foundation)
• Telethon Institute for Child Health Research (Subiaco, Western Australia)
• Centre for asthma and respiratory diseases (University of Newcastle, NSW)
• Woolcock institutre of Medical Research (Glebe, NSW)
• The Garvan Institute (Darlinghurst, NSW)
• Cytokine Molecular Biology and Signalling Group (John Curtin School of Medical Research, Canberra)
• The modulation of allergic airways disease by Interleukin-4 and -5: Studies using cytokine deficient mice (McMaster University, Canada)
• Information about asthma (National Asthma Council of Australia)
• The asthma puzzle (Australia Advances, CSIRO) (requires QuickTime)

• Association of the British Pharmaceutical Industry, UK
  • Breathing and asthma – provides information and then asks a series of questions about the respiratory system and asthma.

• National Heart, Lung, and Blood Institute, National Institutes of Health, USA
  • Asthma awareness – provides a list of activities about asthma.

• Minnesota Deprtment of Health, USA
  • Asthma education: An integrated approach – provides a range of activities for teaching about asthma. Activities are aimed at primary age students but could be used with older students.

Activity 1. Structure and function of the human breathing system

1. List the main organs or components that make up the human breathing system.

2. Describe the function of each organ or component.

3. Name a structural feature of each organ or component that helps it carry out its functions.

4. During an asthma attack, which components of the respiratory system are affected? How do these changes alter the function of the breathing system?

Teachers notes

1. The main components of the breathing system are:
   
   • nasal passages;
     
   • pharynx;
     
   • larynx (voice box);
     
   • trachea (wind pipe);
     
   • bronchi;
     
   • bronchioles (lungs);
     
   • alveoli (airsacs);
     
   • capillaries with red blood cells;
     
   • thoracic cavity (including diaphragm, ribs and intercostal muscles).

2. The functions of each component are:
   • nasal passages: warm, moisten and filter air;
     
   • pharynx: channels air to lungs and food and water to the stomach;
     
   • larynx: formation of sounds;
     
   • trachea: passage-way for air (windpipe from throat to lungs);
     
   • bronchi and bronchioles: air passages;
     
   • alveoli: gas exchange (especially carbon dioxide and oxygen);
     
   • capillaries with red blood cells: gas exchange;
     
   • thoracic cavity and diaphragm: ventilation (altering the volume of the chest cavity which changes the air pressure in the lungs).

3. Structural features of components that aid them in functioning effectively:
   • Nasal passages: hairs filter large particles; an abundance of capillaries in the nasal passages help to warm the incoming air.

   • Pharynx: gland cells produce mucus to trap particles.

   • Larynx: vocal cords (elastic ligaments) vibrate when air is directed against them and make sounds. The pitch of the sound is controlled by muscles changing the tension of the cords.

   • Trachea: has reinforcing rings of cartilage to protect the airway in the neck.

   • Bronchi, bronchioles: smooth muscle in the walls of these tubes can relax and contract. Relaxation dilates the lumen of bronchioles producing a larger air passage.

   • Alveoli: these sacs have a lining of thin flattened cells and are surrounded by capillaries facilitating gas exchange between the breathing system and the blood stream.

   • Capillaries and red blood cells: capillaries have thin walls to enable gas exchange. Red blood cells contain haemoglobin that picks up oxygen.

   • Thoracic cavity and diaphragm: the muscle fibres of the diaphragm, and those connected to the ribs, expand and contract to change the volume of the chest cavity.

4. During an asthma attack the smooth muscle of the bronchioles contract. This constricts the air passage and causes breathing difficulties.

Activity 2. Measure the volume of air you can exhale

During an asthma attack the smooth muscle lining the air passages of the lungs becomes constricted and the volume of the air that can be exhaled is decreased. Using a large plastic bottle, you can approximately measure, the maximum volume of air that can be exhaled during forced breathing.

Materials (for each small group)

• 5-litre (or larger) plastic bottle with lid (bottle should be marked with 100 mL gradations);
  
• half a metre of tubing (rubber or plastic);
  
• sink or large plastic container.

Procedure

1. Fill a sink or large plastic container with water.

2. Fill the plastic bottle to the top with water and put the lid on.

3. Turn the bottle upside down in the sink and take off the lid under water.

4. Insert a length of tubing into the bottle as shown in the diagram.

   

5. Take a deep breath and expel all the air in your lungs through the tubing and into the bottle.

6. Record the volume of air you have forced into the bottle.

7. Refill the bottle and set up the apparatus as before.

8. Relax for a few minutes until your breathing pattern returns to normal.

9. Repeat the experiment twice.

10. Average the values you obtain.

Questions

1. How is oxygen used in your body?

2. When does your body need more oxygen?

3. How is the carbon dioxide that you exhale produced?

Teachers notes

Students suffering from respiratory or heart problems should not act as subjects for this activity.

Make sure students do not become competitive in their exhaling.

This activity should be done in groups of two (or more). While one student is exhaling another is needed to stabilise the bottle. Provide a new length of tubing for each student.

You may want students to calculate a class average and determine the standard deviation. Students could compare the average volume exhaled by females with that exhaled by males or they could look for a correlation between volume of air exhaled and height of the student.

Remind students the volume they are measuring is the vital capacity of the lungs which is more than that exhaled during normal breathing (tidal volume) but less than the total lung capacity. (Some air always remains in the lungs because the thorax cannot be completely collapsed.)

Students can also measure the tidal volume of their lungs using the set-up for this activity. They could use the large plastic bottle or a 500-mL cylinder. The plastic bottle will only give a very approximate reading but will show students that the tidal volume is only small compared to the vital capacity.

1. Oxygen is used for aerobic cellular respiration, the process by which sugar molecules are broken down and energy is released.

2. More oxygen is need when more energy is required. More oxygen is required during exercise.

3. During cellular respiration, carbon dioxide is produced. The general equation is:

   oxygen + sugars = carbon dioxide + water + energy.

Activity 3. The effect of exercise on breathing

Exercise can alter the rate of breathing and the carbon dioxide (CO₂ ) content of the exhaled air. This activity will measure the effect of exercise on breathing rate and CO₂ levels in exhaled air.

Materials (for each small group)

• 1 conical flask or small beaker;
  
• 1 100 mL measuring cylinder;
  
• 5 straws;
  
• 1 dropper bottle of sodium hydroxide (chemical formula NaOH);
  
• 1 dropper bottle of phenolphthalein;
  
• 1 stopwatch.

1. Place 100 mL of water in the conical flask and add five drops of phenolphthalein.

2. One member of the team (the subject) should sit quietly for 3 minutes.

3. After the first and third minute take the subject's pulse. (Count the pulse for 15 seconds then multiply by four to determine pulse rate per minute.)

4. After the second minute, test the CO₂ level in exhaled breath by having the subject breath through five straws into the solution in the conical flask for exactly 30 seconds. (The subject should keep the straws together so that as little air as possible escapes between them, and breath in through the nose and out through the straws. There is no need to open the mouth at all. At rest the subject should only take about three breaths in 30 seconds.)

5. Rinse the straws, and put them aside for later.

6. Add one drop of NaOH solution to the flask. Swirl the contents vigorously and observe the flask against a white background. Look for evidence of a pink colour.

7. If no pink colour appears, add another drop of NaOH solution, swirl vigorously and check colour again.

8. Keep a count of the number of drops used.

9. Continue adding drops until the solution in the conical flask turns pink and retains its colour for a least 15 seconds.

10. Record the number of drops used.

11. Wash out the flask and refill with another 100 mL of water and five drops of phenolphthalein.

    You now have two resting pulse measurements and one measurement of CO₂ levels in exhaled air when the subject is at rest.

12. The subject should now run on the spot or do star jumps for 2 minutes, working as hard as possible for the full time.

13. As soon as possible after the exercise stops and while the subject is seated, take a pulse measurement and have the subject breathe out into the conical flask.

14. Repeat the pulse measurement every 2 minutes and the CO₂ measurements at 4 minutes and 8 minutes during the 10 minutes of recovery time. (The subject should remain seated during the recovery period.)

15. Record your results in a table, then graph the data obtained from your subject.

Questions

1. If the average heart pumps about 80 mL of blood with each contraction, calculate the volume of blood pumped by the subject:
   • at rest;
     
   • immediately after vigorous exercise;
     
   • 10 minutes after completing exercise.
     

   (Your answers should be in mL/minute.)

2. Calculate the percentage increase in heart rate from rest to immediately after exercise.

Teachers notes

Students suffering from respiratory or heart problems should not act as subjects for this exercise.

Preparation

• It may be helpful to provide two conical flasks (or beakers) per group of students.

• If the titration is taking a long time, another CO₂ sample can be taken in the second flask.

• Five straws are the maximum needed per subject.

  Since straws vary in diameter, you should experiment with yours to determine how many are needed to give an even delivery of exhaled air into the phenolphthalein solution. (Using multiple straws to exhale through minimises bubbling.)

• Ask subjects to practise breathing out through the straws before beginning the activity.

• If you have more than one subject per group, you will need a new set of straws for each new subject.

• Phenolphthalein solution: dissolve 1 gram of solid phenolphthalein in 500 mL methylated spirits.

• NaOH solution: 0.01 M (0.4 grams NaOH made to 1 litre with water).

• Students should measure the pulse rate by using the tips of the fingers just on the outside of the major vein on the thumb side of the front side of the subject's wrist. Ask students to practise this before beginning the exercise.

Summary of data collection

At the end of the experiment students should have:

• heart rate measurements taken 3 minutes before exercise started and 1 minute before exercise started;

• heart rate measurements taken at 2-minute intervals during a 10-minute recovery period;

• CO₂ measurements taken 2 minutes before exercise started;

• CO₂ measurements taken at 4-minute intervals during an 8-minute recovery period.

CO₂ concentration is measured by titration. When CO₂ dissolves in water it forms a 'weak' acid (carbonic acid). By measuring the amount of NaOH needed to neutralise this acidic solution, a relative measure of the amount of CO₂ is obtained – the more NaOH needed, the more CO₂ has been exhaled.

Activity 4. How an asthma attack causes breathing difficulties

• Explain why this closes off the smaller airways and causes breathing difficulties.

Teachers notes

The large airways to the lungs are supported by cartilage. However, the smallest airways (bronchioles) which lead to the air sacs (alveoli) are supported only by smooth muscle. When these muscles tighten or spasm, this makes the opening of the airways much narrower than usual so it is hard to move air in and out of the air sacs. In addition to the effect of the muscles tightening, the thin linings inside the airways swell and thick mucous plugs the airways. The symptoms experienced by an asthma sufferer are: breathlessness, wheezing, chest tightness and coughing.

Further reading

16 April 2005, pages 34-39
Filthy friends and the rise of allergies (by Garry Hamilton)
Discusses the theory that commensal microbes regulate the response of the immune system to allergens.

RTD Info
May 2004
The allergy enigma
Looks at the epidemiology of allergies and sources of environmental allergens. Also includes boxed information ‘Data on plant proteins’ and ‘Apples, false friends’.

Science Daily
27 Octobert 2010
What can country of birth tell us about childhood asthma?
Compares country of birth and socioeconomic status on the prevalence of childhood asthma.

17 August 2010
Ozone and nicotine a bad combination for asthma
Outlines how second hand tobacco smoke can combine with ozone forming dangerous ultrafine particles.

5 July 2010
Ultrafine particles in air pollution may heighten allergic inflammation in asthma
Describes the role of ultrafine pollution particles in causing allergic airway inflammation.

1 June 2009
Caffeine shown as effective at reducing exercise-induced asthma symptoms as an albuterol inhaler
Ingesting caffeine within an hour of exercise may reduce the symptoms of exercise induced asthma.

9 April 2010
Traffic-related pollution near schools linked to development of asthma in pupils, study suggests
Suggests that traffic-related pollution near schools contributes to the development of asthma in children.

25 March 2010
Breathe easy: a natural fruit compound may help asthma
Natural chemicals from blackcurrants may help breathing in some types of asthma

June 2000, page 19
Asthma worldwide (by Roger Doyle)
Shows increases in the prevalence of asthma and its distribution.

Useful sites

Asthma CRC (The cooperative research centre for asthma and airways)

A joint research venture between Australian medical research institutes, universities and pharmaceutical companies
http://www.asthma.crc.org.au/

About asthma (Asthma NSW, Australia)

A wide range of information for patients to help them understand and manage their asthma.
http://www.asthmansw.org.au/content.cfm?id=2160&menulink=602&subid=0&menuid=602

National Asthma Council Australia

Up-to-date information about asthma for the general public, patients and health professionals. The Asthma Management Handbook is available on-line at this site.
http://www.nationalasthma.org.au

Asthma in Australia 2008 (Australian Institute of Health and Welfare)

Provides information on the prevalence and management of asthma in Australia, including a chapter focusing on asthma in indigenous Australians.
http://www.aihw.gov.au/publications/index.cfm/title/10584

The Lung Net: Learn about lung health (Australian Lung Foundation)

An excellent collection of fact sheets and illustrations about respiratory diseases and lung function. The fact sheets relating directly to lung function and asthma are: 'The lungs - an overview of how they work'; 'Asthma and scuba diving'; 'Asthma in exercise and sport'; 'Controlling adult asthma'; 'Controlling childhood asthma'; 'Occupational asthma'; 'Corticosteroid therapy in respiratory disorders'; and 'Lung function tests'.
http://www.lungfoundation.com.au/content/view/8/8

Australian Broadcasting Corporation (transcripts)

• Tomatoes fight asthma (Catalyst, 12 October 2006)
  Reports on two Australian studies on the prevention of asthma and a new vaccine.
  http://www.abc.net.au/catalyst/stories/s1763143.htm

• Asthma (Catalyst, 17 March 2005)
  Australia has one of the highest incidences of asthma in the world and it's on the increase. This is because current treatments, while vital, only alleviate the symptoms.
  http://www.abc.net.au/catalyst/stories/s1325779.htm

• Treatment of children with asthma (The Health Report, 6 November 2000)
  Discusses studies that compare various preventative medications for asthma.
  http://abc.net.au/rn/talks/8.30/helthrpt/stories/s209191.htm

Asthma overview (British Broadcasting Corporation, UK)

Provides information about the symptoms, causes, common triggers and treatment of asthma.
http://www.bbc.co.uk/health/conditions/asthma/

Asthma (Health System, University of Virginia, USA)

An explanation of asthma and what happens during an asthma attack.
http://www.healthsystem.virginia.edu/uvahealth/peds_respire/asthmhub.cfm

How your lungs work (How Stuff Works, USA)

Describes how you breathe, where the air goes, how breathing is controlled and diseases that affect your lungs.
http://www.howstuffworks.com/lung.htm

Glossary

airways. A general term for the system of tubes that runs from the back of the mouth and nose into the lungs. The largest is the trachea or windpipe. In the chest, the trachea divides into two smaller tubes called bronchi. Each bronchus then supplies one lung. After entering the lung, the bronchi divide further into narrower tubes called bronchioles and these supply the air sacs of the lung. The airways contain a thin lining on the inside moistened with a little mucus. Barring choking or drowning, from the moment you are born your airways are kept clear and, unless you smoke, fairly clean. Asthma sufferers find that periodically their airways narrow and they can't breathe normally. The smooth muscle is contracting and so narrowing the airway, and at the same time the inner lining becomes inflamed and reddened. It may also swell. Extra mucus is produced, sometimes thicker than usual, and it can partially clog or obstruct the airway.

allergens. An allergen is any substance that triggers an allergic reaction. Common respiratory allergens are grass pollen, mould spores or house dust mite faeces (present in dust); other allergens may affect the skin or the digestive system.

allergic reaction. Allergies are inappropriate reactions of the immune response to substances (allergens) that normally wouldn’t cause any noticeable effects. Most allergic reactions involve the allergen binding on to special immune system cells and causing these cells to release compounds that affect the surrounding tissue. One such compound is histamine. It causes itching and inflammation. Chemicals that block the effect of histamine are called antihistamines, and they are standard allergy medication. However, they are not particularly effective in asthma.

bronchodilators. (Also called 'relievers'.) These are a group of drugs that relax the smooth muscle in the airway walls and hence widen (dilate) the airways. Used to relieve the symptoms of an asthma attack.

chronic. Used to describe a medical condition that continues for a long time, often with little change. A chronic disease, such as asthma, may have acute episodes, when the situation worsens for short periods of time.

cytokine. A hormone-like molecule, produced by one cell, that has an effect on another cell. Some types of cytokines are normally produced in low concentration by the immune system as part of the body's defence mechanism. Some cytokines are toxic at high concentrations and cause disease symptoms such as fever.

eosinophil. A white blood cell that increases in number as a result of certain parasite infections and allergic diseases.

epithelium/epithelial. A tissue composed of cells that line the cavities and surfaces of structures throughout the body. In the lung, the epithelium is a thin layer of cells which lines the airway tubes in order to protect and regulate the tissue underneath.

extrinsic. External or a cause coming from outside. In this type of asthma, the cause of an attack is normally the inhalation of an allergen. Extrinsic asthma is more likely than intrinsic to start in childhood, and often the trigger(s) can be identified and dealt with. In extrinsic asthma, the reaction of the airways is like an allergic reaction, and is similar to hayfever and other allergies.

gene. The basic unit of inheritance. A gene is a segment of DNA that specifies the structure of a protein or an RNA molecule.

house dust mites. Tiny mites (about one-third of a millimetre long) that feed off human skin flakes and bodily secretions. They colonise houses, especially in warm, humid areas. They tend to live in carpets, mattresses, pillows and soft furnishings. Although quite harmless, their droppings contain substances that are allergens. Exposure to the droppings (invisible to the eye) can cause sneezing, itchy, red eyes or asthma attacks.

inflamed/inflammation. Inflammation is the process that makes living tissue swell, become painful and turn red. Inflamed tissue contains damaged cells and has a higher than normal blood flow through it – that is why it’s red and warm. It is usually ‘infiltrated’ by many cells of the immune system. Compounds released from damaged cells cause fluid and more inflammatory cells to leak out of the blood vessels in the area; this fluid accumulates and may make the tissue swell or block tubes. Inflammation is often associated with infection but it can also be caused by allergic reactions. One of the major inflammatory cells in asthma is the eosinophil, which can damage the airway lining. This can ultimately lead to permanent damage in the airways. Inflammation of the lining of the nose, for example, causes the blocked nose characteristic of colds or of hayfever. Inflammation of the airways occurs in asthma, but is not unique to it.

interleukin. A chemical messenger secreted by cells of the immune system. They act by affecting the behaviour of the rest of the immune system. For example, they may attract immune system cells to an area of the body or they may stimulate the development of some cells of the immune system.

intrinsic. Instrinsic asthma has no clear connection with allergy. It can start at any age. The triggers are usually infection, polluted air, exercise, or cold temperatures, but some attacks occur without any obvious trigger.

nitrogen oxides. Chemical formula NO_x. This covers the gases nitric oxide (chemical formula NO) and nitrogen dioxide (chemical formula NO₂ ). Both can be toxic but nitrogen dioxide is considered to be of most concern for asthmatics. The main source of the gases in urban areas are motor vehicle exhaust and gas cookers and kerosene heaters indoors. The brown haze sometimes seen over cities is mainly nitrogen oxides. These gases are also partly responsible for the generation of ozone, when acted upon by sunlight in the presence of other chemicals. Although air pollution can cause irritating symptoms and increased asthma symptoms in some people, it is unlikely to be an important cause of asthma in Australia.

microRNA. A short piece of single-stranded RNA that does not encode a protein. They have a number of functions including regulating the expression of genes.

occupational sensitisers. Chemicals or compounds that causes airway inflammation leading to asthma. These sensitisers occur in particular occupations such as carpentry (eg, western red cedar wood dust is a sensitiser) and commercial spray painting (some duco paints are sensitisers).

ozone. Ozone (O₃ ) is a form of oxygen. It is a colourless gas that has a very pungent odour. It exists naturally at low concentrations in the stratosphere where it absorbs ultraviolet radiation. In the troposphere it exists naturally at extremely low concentrations. But these concentrations increase when sunlight acts on various gases, coming mainly from vehicle exhausts, and ozone then becomes a pollutant in the troposphere. Ozone is a highly corrosive gas and is poisonous to most organisms. At concentrations as low as 0.00001 per cent (or 10 parts per hundred million) it can irritate the membranes lining the nose, throat and airways and can trigger or exacerbate asthma attacks.

prebiotics. Non-digestible carbohydrates that stimulate the activity and growth of beneficial bacteria in the digestive system.

probiotics. Cultures of live microorganisms that can be taken to improve the balance of natural microflora in the digestive tract.

protein. A large molecule composed of a linear sequence of amino acids. This linear sequence is a protein's primary structure. Short sequences within the protein molecule can interact to form regular folds (eg, alpha helix and beta pleated sheet) called the secondary structure. Further folding from interaction between sites in the secondary structure forms the tertiary structure of the protein.

Proteins are essential to the structure and function of cells. They account for more than 50 per cent of the dry weight of most cells, and are involved in most cell processes. Examples of proteins include enzymes, collagen in tendons and ligaments and some hormones. More information can be found at Protein structure and diversity (Molecular Biology Notebook, Rothamsted Research, UK).

RNA (ribonucleic acid). A nucleic acid similar to DNA. There are a number of types of RNA, the major ones being messenger RNA, transfer RNA and ribosomal RNA. RNA can serve as a messenger between DNA and proteins, as a structural molecule, as an enzyme and as regulators of gene expression. In some viruses RNA is the genetic material. For more information see Introduction to RNA and its functions (University of Newfoundland, Canada).

smooth muscle. All airways have bronchial smooth muscles in their walls. These muscles are classed as 'smooth' muscle. This means they are not under voluntary control, like the muscles of our legs and arms, but instead respond to circulating hormones and compounds released locally by damaged or inflamed tissue. Many drugs will cause changes in smooth muscle without any effects on our voluntary muscles. Smooth muscle contraction will narrow airways and can also constrict arteries and many other tubes in the body. Smooth muscle relaxation will dilate (widen) these tubes.

sulfur dioxide. Sulfur dioxide (chemical formula SO₂ ) is an acrid-smelling gas that even at low concentrations irritates the membranes of the nose and respiratory system. It is thought to exacerbate many respiratory diseases, including asthma. Sulfur dioxide is produced whenever sulfur-containing compounds are burnt. Its commonest source in Australia is power-stations burning coal containing slight sulfur impurities.

T-cell. White blood cells that are important for the body's immune response to specific antigens. Killer T-cells are like soldiers who search out and destroy invading bacteria or viruses or cancer cells.

trigger. A stimulus that causes asthma symptoms or an attack. Triggers include irritants such as fumes, cigarette smoke, allergens such as house dust mite or moulds, viral respiratory tract infections, and exercise. Not every asthmatic responds to every trigger. And not every asthmatic responds to the same trigger in the same way on each exposure. Some triggers, such as allergens, can cause worsening airway inflammation.

white blood cell. (Also known as leucocytes.) White blood cells are the immune system cells. They can be divided into many different categories on the basis of their function and appearance. Many are not found in the blood at all and those that are may have the ability to crawl out of blood vessels, squeezing between the cells of the vessel walls. While some produce antibodies, others produce cocktails of destructive chemicals, others kill virus-infected cells by punching holes in them, and a further class control the entire immune response. For more information see White blood cells (Puget Sound Blood Center, Washington).