What is asthma?
Most people know, or know of, a person with asthma – about one in every 10 people are sufferers. The word asthma usually brings to mind a picture of someone who has difficulty breathing or is breathless and wheezy. Yet, though asthma is easy to recognize, it is difficult to define.
The symptoms of asthma are caused by the narrowing of the bronchi, which are the myriad tubes in the lungs. Air is breathed into the lungs through the trachea (windpipe) which divides into two main branches, known as the major bronchi. These then divide in each lung into many smaller bronchi.
While breathing is normally a reflex action of which we are mostly unconscious, in asthma it becomes a conscious effort as the narrowed bronchi slow the movement of the air into and out of the lungs.
In asthma breathing out is usually more difficult than breathing in. The wheezing, whistly noise is the sound of air being pushed out through the narrowed airways.
There are three main causes of narrowed bronchi. The first is mucus which is normally carried upwards towards the mouth by fine hairs called cilia which line the bronchi. The airway will be narrowed if excess mucus is produced or if the cilia do not clear the mucus from the lungs efficiently.
The bronchi can also be blocked by the swelling of the tissue lining the bronchi, which is loose and swells easily. The third way the bronchi can be blocked is by contraction of the muscles which wind around them. This contraction of the muscle is called bronchospasm.
A narrowed airway can be caused by one or all three of these factors. It is not known exactly why the airways of the patient with asthma should narrow, but in each case, the airways are sensitive and irritable.
Before an attack of asthma, a patient may complain of a heavy chest and coughing. During an attack he or she may suffer from wheezing, the pulse may be rapid and the skin sweaty or clammy.
Surprisingly, the wheezing sound is often louder as an asthma attack subsides rather than during it. A cough often accompanies an attack and phlegm (a sticky, clear or whitish mucus) from the swollen bronchi may be present.
How severe is it?
The incidence of asthma differs from country to country, varying from as little as one percent of the population to as much as 20 percent. In pre-school and early age children, up to 20 percent have asthma. In adolescents, this figure drops back to less than five percent.
During childhood, more boys than girls suffer from asthma. Many develop asthma during adulthood, and this late onset of asthma is more common in women than in men.
Most children have mild asthma, with infrequent bouts of wheezing which settle without medical treatment. Those with frequent severe bouts will require medical treatment.
Doctors can determine the severity by listening over the chest with a stethoscope, which will pick up narrowing not noticed by the sufferer.
Measuring devices such as a Spirometer will also give an indication of the degree to which the airway is obstructed and are more sensitive than either the patient or the stethoscope.
A useful development in measuring the severity of asthma are home air flow meters which allow the patient to measure his asthma throughout the day. They are ideal for patients who prefer not to take regular medication, as they indicate when the lung function is decreasing and so give a warning to take medication before a severe attack occurs. Such a meter is more sensitive than reflexes and senses, as many patients are not aware of decreasing lung function.
Causes are complex
The airways of people who suffer from asthma are more sensitive than normal. Yet each asthmatic will respond to different stimuli and any factor may cause an attack one day and not the next. The stimuli that may trigger an attack differ from person to person and one might cause hay fever in one person and a severe attack of asthma in another.
Why some people have more sensitive bronchi than others and why different bronchi react to different factors is not known. Factors that can trigger asthma include head colds or influenza, exercise, weather changes, climate, emotional stress, and allergies to pollens, dust, animal dander (dandruff) and house dust mites.
Allergy is altered reactivity to foreign substances known as allergens. The first type of allergy is known as immediate because there is an almost immediate response to the allergen. The second group occurs a couple of hours after contact with the allergen.
Inhaled trigger irritants that can cause an attack of asthma include the pollens of grasses, weeds, trees and plants, fungi and molds, and also insect particles, house dust mites and animal dander.
When allergens such as these are inhaled, they enter the body through the surface layer of the airways and antibodies are formed. Antibodies cling to cells called mast cells, found clustered in the bronchi. When antibody and allergen meet, the wall of the mast cell breaks down causing chemical substances to be released.
An example of these substances is histamine which has a double action. Histamine causes fluid to leak into the lining tissues which then swell, and stimulate the bronchial muscle and cause it to contract. Use of medicine such as Intal before contact with a known allergen coats the mast cells and prevents the secretion of these substances.
Pollens: The main offending pollens come from grasses, trees and weeds. Many asthmatics have a history of hay fever from these allergens. The best way to avoid such allergens, and you can’t always avoid pollen or eradicate it, is to avoid freshly mowed lawns and country bush areas during pollen seasons. Use good air-conditioning if you spend a large amount of time indoors.
Molds: Moulds thrive on warm, moist conditions so a regular and thorough cleaning of your cupboards, floors and ceilings is necessary. Foods susceptible to mold growth include vegetables, fruit, stale bread and cheese. Keep vegetable containers, refrigerator drip trays, garbage cans, household sinks, laundry, toilet and shower areas clean. Avoid damp buildings, do not rake or burn leaves or dry grass and don’t keep indoor plants, or garden compost heaps.
House dust mites: More than 80 percent of asthmatics are sensitive to house dusts and house dust mites. House dust mites are invisible to the naked eye and thrive and breed in a temperature of about 25 degrees C.
They are not parasitic – they eat only shed human skin scales.
To minimize contact with dust mites, keep your house dust free and vacuum regularly – particularly mattresses, rugs and carpets. Cleaners with filters on them are good. Wear a gauze mask or put a wet handkerchief to your mouth while vacuuming and allow time for dust to settle before removing it.
Avoid pillows, mattresses and quilts filled with kapok, feathers or cotton. Vinyl mattresses are the best. Keep bedding and rooms in the sun as much as possible.
Weather: Weather and temperature changes can cause asthma attacks but no particular climate can be said to be better than another.
Animals: Dander (dog or horse dandruff, for instance) can trigger an attack. Some people get asthma not only from animal dander but also from animal-based products, such as furs or poultry feathers in cushions and quilts.
Role of exercise
Exercise is another common trigger to an asthma attack and it is estimated that as many as 75 percent of asthmatics will have asthma induced by prolonged exercise (6 to 8 minutes). After a running treadmill test given to 652 patients in Sydney, 81 percent had exercise-induced asthma (EIA).
EIA can be diagnosed by demonstrating a fall in the forced expiratory volume of air in one second or a peak expiratory flow rate of 10 percent or more of the pre-exercise level after 6 to 8 minutes of exercise.
In most people, this is about 80 percent of their total capacity. An asthma patient will deliver less than that, possibly as low as 20 percent of his total capacity.
Peak expiratory flow is measured by a device that locks when peak airflow is reached, normally between 400 and 600 liters a minute. In asthma, this figure may drop to 200 to 400.
For both these testing procedures measurement will vary according to height, age and sex. These methods of assessing lung function are simple to perform and usually use cheap and portable equipment.
Three factors determine EIA. The first is the type of exercise performed. Running is the exercise most provocative of asthma while swimming and walking are least likely to induce an attack.
The second factor is the duration of the exercise. A brief exercise for one or two minutes will improve lung function. In most patients, 6 to 8 minutes of exercise will induce an attack. However, research has indicated some complexities in this response.
The third factor is the intensity of exercise. Intense exercise is more likely to cause an attack and to consistently bring on asthma a patient would have to exercise to 80 percent or more of his maximum capacity.
Research now indicates that the initiating stimulus for EIA is the loss of heat and water from the respiratory tract as a result of increased ventilation during exercise. Air expired during exercise is fully saturated with water vapor and when exercise is performed for six to eight minutes up to 20ml of water can be lost from the airways.
The duration and intensity of exercise will determine the level of ventilation and the consequent loss of heat and water. Asthmatics vary in their sensitivity to this effect on the airways.
There are other stimuli that play a role in EIA and the mechanism by which exercise induces an attack is still not clear. There are two approaches to the management of EIA – it can be treated as it occurs or the patient can use a therapy to prevent it.
In most patients, EIA asthma will be reversed by the use of a beta-sympathomimetic aerosol which induces bronchodilation and has a preventative action. In sports such as swimming it may be impractical to carry an aerosol, but use directly before exercise will prevent an attack.
The aerosol treatment has several advantages over oral treatment. Firstly, it is immediately effective and may be used at short notice. Secondly, the dose is only a fraction of that which is required orally and thirdly, the medication is not dependent on gastrointestinal absorption.
Asthmatics should be encouraged to exercise. It is advisable to warm up first then exercise in short bursts rather than in prolonged stints.
Finally, they should use medication, such as a bronchodilator, immediately before exercise since the blocking effect of medication on EIA is brief.
An allergy to a food can bring on an asthma attack. Children under five often have an allergy to foods such as cows’ milk, eggs, fish, chocolate or legumes that can trigger an asthmatic response. In adults, such an allergy to food is very rare and is not a major factor in asthma.
However, sensitivity to food components, such as food additives and coloring agents, is more common. These components cause the bronchi to overreact and provoke an asthma attack. Examples of natural food components are salicylates, occurring in tea, tomatoes, many fruits, and some vegetables.
Food additives and preservatives include metabisulphite and benzoates which are mainly used in liquid and fruit-based products such as soft drinks, cordial and dried fruit. Large quantities of these can have an adverse effect.
These substances act in the following way. The pathways of inflammation are an integral part of our immune response used in combating infection. Substances such as salicylates interfere with these pathways with the result that there is a lowering of the threshold for inflammation. An allergy, therefore, could be considered to be cellular inflammation or a misfiring of our immune system.
In severe asthmatics, it is important to be aware of sensitivity to foods and food components. An allergy to a particular food is usually easy to determine and while a full exclusion diet will rarely cure asthma, recognition of individual sensitivities may decrease symptoms.
Sprays and tablets
An attack of asthma can last from a few minutes to a couple of hours. In most cases, the attack will pass naturally. Although there is no treatment or drug that will cure asthma, there are many medicines available that will ease an attack, or if used before contact with a known precipitant, will help to prevent one.
The first group of medicines are those given during an attack, called bronchodilators because they relax the muscle spasm during the attack. There are two types of bronchodilators – sympathomimetics and xanthines – which act in slightly different ways. One of each type is often administered.
Medicines in the sympathomimetic group include Alupent, Berotec, Bricanyl and Ventolin, and these are prescribed as tablets, mixtures or inhalants.
Inhalation of these drugs usually gives faster results.
However, it is important that the inhaling technique is correct as the spray won’t work if it doesn’t get into the lungs. Inhaling is not always suitable for the elderly or the very young who might not be able to coordinate their breathing with the discharge of an aerosol canister.
The second group of bronchodilators contain theophyllines and are usually taken by mouth. Drugs in this group include Androphyllin, Brondecon, Nuelin and Elixophyllin.
For severe asthma attacks, corticosteroids are often prescribed with bronchodilators. Corticosteroids are derived from cortisone and when used with bronchodilators will improve their action and effects.
Corticosteroids are a preventative medicine which, if used regularly, can prevent severe attacks from developing. Examples are Becotide and Aldecin which can be taken by inhalation using a metered aerosol.
The side effects of cortisone include obesity, acne and a puffy face but when used in small doses by aerosol the effects are minimal.
The third medicine prescribed is Intal, again a preventative medicine which helps to avert an attack if used regularly. In some patients, Intal will prevent an attack if used before contact with a known trigger factor, such as dust or pollen or exercise.
Other medicines that may be prescribed include antihistamines that combat the histamines released from allergic reactions, cough mixtures, mucolytics and expectorants which clear and thin the sputum. These are considered to have only limited value.
Antibiotics may be prescribed to treat bronchitis or chest infections to which people with asthma are more prone.
Desensitization injections can be prescribed to help build up immunity to know allergens to which a patient is particularly sensitive. But these injections may have side effects and are not particularly effective in all cases.