Chronic obstructive pulmonary disease and asthma

In this chapter, we will describe definitions of chronic obstructive pulmonary disease (COPD) and asthma, possible mechanisms, time trends, and population patterns of prevalence, and evidence regarding the causes of both diseases. COPD and asthma are highly prevalent non–malignant respiratory conditions that have increased dramatically in the past few decades, both in Western and non–Western societies. They have a profound impact on the quality of life for patients and their families, and COPD is also a major cause of death.

The major causal risk factor for COPD is tobacco smoke, although a substantial proportion of COPD is also caused by occupational exposures and indoor environmental exposures, particularly in middle- and low-income countries. Although cigarette smoking is the major risk factor for COPD, usually only a relatively small proportion of smokers develop COPD, a pattern which may be explained by genetic susceptibility factors. Similar to asthma, COPD prevalence differs greatly between countries and these differences are not explained by cigarette smoking alone. Nonetheless, smoking cessation is the most effective way to halt global increases in the prevalence of COPD. Improved indoor ventilation measures to reduce indoor pollutants in houses of most middle- and low-income countries are also effective ways to reduce morbidity and mortality, particularly in the developing world.

A large number of potential risk factors for asthma have been identified including genetic factors, allergen exposure, demographic parameters, diet, obesity, indoor and outdoor pollution, passive and active tobacco smoking, occupational exposures, viral infections, and the use of paracetamol (acetaminophen). However, none of these risk factors on their own appear to explain the substantial global increases in asthma prevalence observed over the last few decades. They also cannot explain the significant differences in asthma prevalence between countries. Interestingly, recent studies have shown that the increase in asthma prevalence appears to have levelled off in many high-income countries, with some even showing a decrease. The reasons for this are unclear. Understanding why these changes in prevalence are occurring, and ascertaining which elements of the ‘package’ of twentieth-century economic development and lifestyle changes are responsible, is essential in order to develop effective intervention programmes to halt the current global asthma epidemic.