Definition

In 2004, the UK National Institute for Clinical Excellence defined chronic obstructive pulmonary disease (COPD) as “characterised by airflow obstruction. The airflow obstruction is usually progressive, not fully reversible and does not change markedly over several months. The disease is predominantly caused by smoking.” COPD is the preferred umbrella term for the airflow obstruction associated with the diseases of chronic bronchitis and emphysema. These are closely related to, but not synonymous with, COPD.

Although asthma is associated with airflow obstruction, it is usually considered as a separate clinical entity. Some patients with chronic asthma also develop airflow obstruction that is relatively fixed (a consequence of airway remodelling) and often indistinguishable from COPD. Because of the high prevalence of asthma and COPD, these conditions coexist in many patients, creating diagnostic uncertainty. Other conditions also associated with poorly reversible airflow obstruction include cystic fibrosis, bronchiectasis, and obliterative bronchiolitis. Although these conditions need to be considered in the differential diagnosis of obstructive airways disease, they are not conventionally covered by the definition of COPD.

Prevalence of diagnosed COPD in UK men and women during 1990-7

Epidemiology

Prevalence

Estimating and comparing the prevalence of COPD in different countries is complicated by differences in its precise definition and in the level of underdiagnosis. For example, in the United Kingdom mild COPD is defined as the ratio of forced expiratory volume in 1 second (FEV₁) to the forced vital capacity (FVC) being < 0.7 and the FEV₁ being 50-80% of the expected value. Other guidelines suggest slightly different spirometric values (see third article in this series).

Prevalence of diagnosed COPD in UK men and women by age, during 1990-7

A national UK study reported an abnormally low FEV₁ in 10% of men and 11% of women aged 16-65 …