Asthma

Asthma explained

Asthma is a long-standing (chronicA disease of long duration generally involving slow changes.) condition of the respiratory system. The key features are:[1,2]

  • Obstruction of the airways; this varies depending on the time of day and any triggers that may be present
  • Airways obstruction that is reversible, that is, it can be relieved by medication
  • Inflammation of the airways.

In fact, it is thought that asthma is not a single disease but a group of conditions, which have different patterns of illness and development, and different causes and triggers.[1,3,4]

The symptoms of asthma may be described as episodic or persistent - that is, they may occur sporadically or may be continuous - and can vary in their severity.[3]

The World Health Organization estimates that 300 million people had asthma in 2005.[5] Asthma has been reported to be most common in the UK, Australia and New Zealand - in these countries, 15 per cent of children are affected.[6]

Symptoms and signs

The symptoms of asthma include:[1,2,7]

  • Intermittent wheezing
  • Shortness of breath
  • Chest tightness
  • Cough, with or without sputum.

Wheezing is caused by a narrowing of the small airways. This narrowing happens for three reasons: swelling of the airways with excess fluid (oedemaThe accumulation of excess fluid in the tissues of the body.), contraction of the smooth muscleA type of muscle responsible for actions in the body that we are not aware of; for example, the muscles that constrict blood vessels. within the walls of the airways, and excess mucus.[3] Narrowing of the airways makes it more difficult to take in air when breathing in.

Often, symptoms are initially experienced only when someone has a viral respiratory tractThe parts of the body that are involved in respiration. The respiratory tract includes the nasal passages, throat (pharynx), windpipe (trachea), bronchi and lungs. infectionInvasion by organisms that may be harmful, for example bacteria or parasites.. Over time these symptoms may become more persistent, however, occurring even when there is no infectionInvasion by organisms that may be harmful, for example bacteria or parasites. present.[7]

The symptoms of asthma are frequently:[2]

  • Worse at night and early in the morning
  • Brought on by exercise or exposure to allergens or cold air
  • Worsened by certain medications such as aspirin or beta-blockersA group of drugs that block beta-receptors to slow the heart rate, or constrict the airways and arteries.
  • Associated with conditions of allergic hypersensitivity (atopy) such as hay fever or eczema.

When examined by a healthcare professional, people with asthma may be found to have a widespread wheeze in the chest that can be heard with a stethoscope. Those with severe asthma may use extra muscles of respiration (called the accessory muscles) to maximise the amount of air drawn into the lungs. Many people have no physical signs of asthma at all.[2]

Exacerbations of asthma involve airway inflammationThe body’s response to injury. and obstruction and may be triggered by viral or bacterial infectionInvasion by organisms that may be harmful, for example bacteria or parasites., an allergy, or some other environmental exposure. Often, there is a combination of underlying causes.[8]

Risk factors and prevention

A family history of asthma is a clear factor in determining whether or not someone will develop the condition. However, a person's geneticRelating to the genes, the basic units of genetic material. predisposition is most likely to have an effect when combined with environmental factors such as:[4]

  • Infection
  • Poor nutrition (for example, a low intake of fish or fish oil during pregnancy)
  • Stress
  • Smoking during pregnancy (which increases the risk of the child later developing asthma)
  • Mode of delivery (having been delivered by emergency Caesarean section appears to increase a child's risk of asthma).

Additional risk factors include:[4,9]

  • Obesity
  • Sensitisation to, for example, house dust mite, cat or cockroach allergens
  • Certain occupations such as hairdressing or cleaning, or jobs that involve spray-painting.

In addition, exposure to tobacco smoke and air pollution may worsen pre-existing asthma.[4]

Tests and diagnosis

Lung function testing (spirometry) is helpful in diagnosing asthma. The key measurements taken are:[1,2,10]

  • The forced vital capacity (FVC, the maximum volume of air you can exhale)
  • The forced expiratory volume in one second (FEV1, the maximum volume of air you can exhale in one second).

From these measurements, the FEV1/FVC ratio can be calculated.[2]

Among people who do not have an obstructive lung condition such as asthma, the FEV1/FVC ratio is usually greater than 0.80.[2]

Airflow obstruction is shown to be reversible if there is an improvement in someone's FEV1 after using an inhaled beta-agonist, a type of medicine known as a bronchodilator that expands the airways, or after two weeks of using an inhaled corticosteroid or leukotriene receptor antagonist - both are types of anti-inflammatoryAny drug that suppresses inflammation medications.[1,2]

Another test that can help in the diagnosisThe process of determining which condition a patient may have. of asthma is the peak expiratory flow rate (PEFR). A peak flow meter is used to assess the fastest rate at which the person can exhale air. Variation in the PEFR indicates that the person has asthma; this is also the case if someone shows an improvement following the use of a bronchodilator.[2,3] In addition, the PEFR is helpful in assessing how well someone's asthma is controlled.[10]

Chest X-rays or computerised tomographyA scan that generates a series of cross-sectional X-ray images. (CTA scan that generates a series of cross-sectional X-ray images.) can help to rule out other conditions, and may be useful if someone is not responding to asthma therapy.[2,3] The most common feature seen on the chest X-rays of people with asthma is thickening of the airways.[1,3]

Skin prick testing is also useful because it can be used to identify any environmental allergies, so that the provoking allergens may be avoided.[2]

Many healthcare providers diagnose asthma based on whether or not asthma medication helps the person's symptoms; however, the diagnosisThe process of determining which condition a patient may have. should be confirmed with testing such as spirometry where possible.[2]

Choosing treatments

Beta-agonists are a type of medication known as bronchodilators - that is, they act to widen (dilate) the main airways by relaxing the smooth muscleA type of muscle responsible for actions in the body that we are not aware of; for example, the muscles that constrict blood vessels. in the walls of the bronchiAny of the main air pipes beyond the windpipe, or trachea, which have cartilage in their wall..

There are two main groups of beta-agonists - short-acting and long-acting. Short-acting beta-agonists are effective for 2-6 hours and are used to relieve symptoms as and when they are needed. Long-acting beta-agonists are effective for over 12 hours. They are used to improve someone's overall asthma control, allowing for prolonged dilation of the airways and protection against spasm of the bronchiAny of the main air pipes beyond the windpipe, or trachea, which have cartilage in their wall..[11]

Corticosteroids are usually inhaled by people with asthma, but may also be taken in tablet form. These medicines, which suppress airways inflammationThe body’s response to injury. and have transformed asthma therapy, should be taken in the lowest dose effective to control symptoms.[10,12,13] High doses may increase the risk of osteoporosis in adults, or lead to short-term suppression of growth in children.[10]

Research suggests that long-acting beta-agonists are best taken by people whose asthma has not responded well to inhaled corticosteroidsA group of hormones that are produced by the adrenal glands, which sit on top of the kidneys..[11]

Leukotriene receptor antagonists are another type of anti-inflammatoryAny drug that suppresses inflammation medicine that appear to be effective in preventing the recurrent wheezing associated with viral infections.[12]

Non-drug measures

Strategies to avoid allergens may include the removal of pets, using covers for mattresses, closing the windows during pollen seasons, certain cleaning measures and the reduction of humidity to kill house dust mites.[2] However, the question of whether or not such avoidance measures are beneficial is controversial.[3]

Breathing exercises may also be helpful. One example, the Buteyko method, which uses techniques that aim to slow ventilation, has been shown to improve asthma symptoms.[14]

Outlook and living with asthma

Acute complications of asthma may include:[1]

  • Pneumonia
  • Free air within the pleural space of the lung (pneumothorax) or space between the lungs (pneumomediastinum). The severity of this condition varies, depending on how serious the person's asthma is and the amount of trapped air.
  • Excess mucus blocking the small airways, with or without the collapse of a lung (atelectasis).

Although the symptoms of asthma usually begin in childhood, they may appear at any age. For those who develop asthma as children, the condition may be lifelong or there may be remission in adulthood. Factors that appear to increase the risk of childhood asthma persisting into adulthood include the severity of symptoms in childhood, poor lung function and being female.[1,4,7]

Education - on the nature of asthma, the possible triggers for exacerbations and their avoidance, and asthma therapy - has been proven to improve the outlook for those with asthma, particularly within a small-group, interactive setting.[15]

References: 
  1. Woods AQ and Lynch DA. Asthma: an imaging update. Radiol Clin N Am 2009; 47: 317-29.
  2. Kaplan AG, Balter MS, Bell AD et al. Diagnosis of asthma in adults. CMAJ 2009 181: E210-20.
  3. Townshend J, Hails S and Mckean M. Diagnosis of asthma in children. BMJ 2007; 335: 198-202.
  4. Subbarao P, Mandhane PJ and Sears MR. Asthma: epidemiology, etiology and risk factors. CMAJ 2009; 181: E181-90.
  5. Link. Last accessed 1 March 2010.
  6. International Study of Asthma and Allergies in Childhood (ISAAC) Steering Committee. Worldwide variation in prevalence of symptoms of asthma, allergic rhinoconjunctivitis, and atopic eczema: ISSAC. Lancet 1998; 351: 1225-32.
  7. Spahn JD and Covar R. Clinical assessment of asthma progression in children and adults. J Allergy Clin Immunol 2008; 121: 548-57.
  8. Sykes A and Johnston SL. Etiology of asthma exacerbations. J Allergy Clin Immunol 2008; 122: 685-8.
  9. Apter AJ. Advances in adult asthma 2006: its risk factors, course, and management. J Allergy Clin Immunol 2007; 119: 563-6.
  10. Pinnock H and Shah R. BMJ Masterclass for GPs: Asthma. BMJ 2007; 334: 847-50.
  11. Walters EH, Gibson PG, Lasserson TJ et al. Long-acting beta2-agonists for chronicA disease of long duration generally involving slow changes. asthma in adults and children where background therapy contains varied or no inhaled corticosteroid (Review). The Cochrane Library 2008; Issue 4.
  12. Townshend J, Hails S and Mckean M. Management of asthma in children. BMJ 2007; 335: 253-7.
  13. Krishnan JA, Davis SQ, Naureckas ET et al. An umbrella review: corticosteroid therapy for adults with acuteHas a sudden onset. asthma. The American Journal of Medicine 2009; 122: 977-91.
  14. Cooper S, Oborne J, Newton S et al. Effect of two breathing exercises (Buteyko and pranayama) in asthma: a randomised controlled trialA study comparing the outcomes between one or more different treatments for a disease (or in some instances, preventive measures against that disease) and no active treatment at all (the placebo group). Study participants are allocated to the various groups on a random basis. May be abbreviated to RCT.. Thorax 2003; 58: 674-9.
  15. Watson WTA, Gillespie C, Thomas N et al. Small-group, interactive education and the effect on asthma control by children and their families. CMAJ 2009; 181: 257-63.