ASTHMA AND COPD
COPD is the major killer with the unfamiliar name. Chronic Obstructive Pulmonary Disease (COPD) is the term now used to describe chronic bronchitis and emphysema. COPD is defined as a preventable and treatable disease characterised by airflow limitation that is not fully reversible and usually progressive. According to the World Health Organization, more than three million people died of COPD in 2005, 90% of them in low- and middle-income countries. By 2030, the WHO predicts that COPD will be the 3rd leading cause of death worldwide. However, data available for these estimates were limited, since COPD is frequently undiagnosed in low- and middle- income countries.
The diagnostic marker for COPD is the deterioration of lung function as shown by a decline in the forced expiratory volume of air in one second (FEV1). The Global Initiative for Chronic Obstructive Lung Disease (GOLD) classifies COPD into four stages based on the percentages of predicted FEV1 from 80% to 30% of normal. The level of FEV1 has been shown to be associated with mortality in COPD patients.
Smoking is the leading risk factor
To date, smoking is the most important risk factor for developing COPD in most countries. The growing burden of COPD is closely related to the epidemic of smoking. To reverse the epidemic of COPD, it is essential to reduce the proportion of the population who smoke. Other factors associated with COPD include specific genetic syndromes, occupational exposures, traffic and other outdoor pollution, secondhand smoke, biomass smoke and dietary factors. Chronic asthma and tuberculosis have also been shown to be associated with irreversible airflow limitation.
Asthma and COPD: Two distinct diseases or different manifestations of the same disease?
Both asthma and COPD are syndromes of airflow limitation, but with significant differences. Typical COPD patients include a high proportion of smokers or ex-smokers; their symptoms rarely develop before age 40; difficult breathing is persistent, progressive and worsens with exertion; night-time attacks of difficult breathing are uncommon; and day-to-day variability of symptoms is rare.
Among asthma patients, a high proportion are non-smokers; symptom onset prior to age 40 is common; variability of symptoms is usual; and patients may be asymptomatic between attacks.
Differences have also been noted in the pulmonary inflammation caused by asthma and COPD in terms of cells, mediators and the anatomic sites of the disease. These differences support the hypothesis that asthma and COPD are distinct diseases with different underlying mechanisms.
However, distinguishing asthma from COPD can be difficult. In reality, there is substantial overlap between them. Patients with asthma who smoke or have been exposed to air pollution may have non-reversible airflow limitation. Likewise, a substantial proportion of patients who meet the definition of COPD have reversible airflow limitation with a positive bronchodilator test, both criteria of asthma. It has been suggested that asthma and COPD are different manifestations of the same underlying disease.
Tracking the prevalence of COPD
Diagnosis of COPD requires spirometry, a test of lung function that measures both the speed and volume of air being inhaled or exhaled. However, quality-assured spirometry is usually unavailable at both primary health care and first-level referral facilities in most countries. Consequently, the majority of patients with COPD are unrecognised or under-diagnosed, especially in low- and middle-income countries.
The Burden of Obstructive Lung Disease (BOLD) Initiative developed a standardised protocol for estimating the prevalence of COPD and its risk factors in various countries around the world. Results from the initial 12 sites (Australia, Austria, Canada, China, Germany, Iceland, Norway, Philippines, Poland, South Africa, Turkey, USA) were published in 2007 and demonstrated that the prevalence of stage II or higher COPD was 10.1% overall, with 11.8% for men, and 8.5% for women.
The PLATINO study, launched in 2002, evaluated the prevalence of COPD in five large Latin American cities: Sao Paulo (Brazil), Santiago (Chile), Mexico City (Mexico), Montevideo (Uruguay) and Caracas (Venezuela). The study showed crude rates of COPD ranged from 7.8% in Mexico City to 19.7% in Montevideo, suggesting that COPD is a greater health problem in Latin America than previously realised.
Like asthma, COPD is mainly treated with inhaled bronchodilators and inhaled corticosteroids. To date, smoking cessation is the only convincing intervention that has reduced the rate of decline of the FEV1 in patients with COPD.
While it is crucial to ensure the accessibility of essential diagnostics and medicines for COPD, tobacco control and reducing exposure to other risk factors for COPD must be given high priority by all countries in their national strategy for the prevention and management of COPD.