Asthma - Cause and Effect
Asthma affects around 300 million people worldwide, making it one of the most common chronic lung diseases. Because asthma is largely a disease of polluted cities, the projected 60% growth in the urban-based population by 2025 will add a further 100 million sufferers to this total.1 The global prevalence of clinically treated asthma is 4.5% but levels vary widely by country. Australia records the highest rate (21.5%), Macau the lowest (0.7%).2
Asthma is a major cause of disability, health resource utilisation and poor quality of life. In episodes of suddenly worsening symptoms, it can be fatal - accounting for almost 1 in every 250 deaths globally. While this rate is relatively low compared to other chronic conditions, it is important to note that asthma doesn't just kill people with severe cases of the disease.
Asthma prevalence is increasing, especially among children according to the Global Initiative for Asthma (GINA) that was launched in 1993 in collaboration with the National Heart, Lung and Blood Institute, National Institutes of Health, and the World Health Organization. This major initiative is being undertaken to improve knowledge about asthma current standards of care and to produce guidelines for clinicians and information for patients.
For people with this chronic condition, exposure to trigger factors causes the lining of the airways to swell and narrow, the surrounding muscles to contract and excessive mucus to be produced. The resulting reduction in airflow causes difficult and laboured breathing. Diagnosis is typically based on a history of respiratory symptoms, evidence of variable airflow obstruction (measured using lung function tests) and the response of the airways to asthma medication.
Factors that influence the development of asthma include (primarily genetic) host factors, such as gender and obesity combined with exposure to environmental factors. Strategies to limit greenhouse gases, ozone, nitrogen dioxide and traffic-related air pollution are needed if asthma incidence is to decrease.3
One of the major barriers to combating the global burden of asthma is that almost one-quarter of sufferers smoke.4 It is known that obese asthmatics are more difficult to treat. Conventionally this has been ascribed to increased thoracic and abdominal fat causing pressure on the airways, but now evidence shows that the adipose tissue itself is metabolically active and produces mediators that act on the airways. Obesity not only complicates asthma but can be causal.5
The spectrum of disease varies but airway inflammation is a consistent feature. The inflammation and associated airway hyperresponsiveness cause recurrent shortness of breath, wheezing, chest tightness and coughing. The airflow obstruction of an asthma attack normally reverses either with, or without, medication.
The severity and the control of asthma are quite distinct features. Severity is assessed by the amount of medication required to limit the disease, whereas control is related to the presence of asthma-related symptoms. One of the best predictors of future asthma attacks is the level of symptom control. When asthma is “controlled”, there are only occasional flare-ups and severe episodes are rare.
Asthma is treated using either long-term “controller” or quick-acting “reliever” medicines, the choice of which is influenced by severity. The aim is to provide the best symptom control using the least amount of medicine. Levels of symptom control may vary over time, requiring adjustments to the medication dosage. Patients are described as “controlled”, “partly controlled” or “uncontrolled” based on the Global Initiative for Asthma (GINA) guidelines.6
1. Masoli, M, et al “Global Initiative for Asthma (GINA) Program: The Global Burden of Asthma: Executive Summary of the GINA Dissemination Committee Report”, Allergy 2004, 59(5):469-478.
2. The World Health Survey (WHS), WHO.
3. “Climate change, air pollution and extreme events leading to increasing prevalence of allergic respiratory diseases” (2013) Multidisciplinary Respiratory Medicine 2013, 8:12 doi:10.1186/2049-6958-8-12.
4. To,T. et al, “Global Asthma Prevalence in Adults: Findings From the Cross-sectional World Heath Survey”, BMC Public Health 2012, 12:204.
5. Dixon, A et al. “An official American Thoracic Society workshop report: obesity and asthma”, Proc Am Thorac Soc. Proceedings of the American Thoracic Society, (2010), p. 325 - 335.