COPD: Overview of Definitions, Epidemiology, and Factors Influencing Its Development: Risk Factor
In addition to cigarette smoke, occupational exposures, and arprotease inhibitor deficiency, etiologies that have been definitely linked to the development of COPD, a number of other factors are likely associated with development of COPD. These include air pollution, passive smoke exposure, respiratory virus infection, socioeconomic factors, nutrition, alcohol ingestion, age, gender, poorly defined familial factors, mucus hypersecretion, and airways hyperresponsiveness. These various factors have been reviewed in detail elsewhere. canadian drug mall
The major risk factor associated with accelerated rate of decline in FEV1 and therefore, the development of COPD, is cigarette smoking. Crosssectional data from a number of studies have suggested that quitting smoking is associated with a reduction in this accelerated rate of decline in FEV1. Thus, an ex-smoker can be expected to lose lung function at the rate of a nonsmoker, although he or she may already have experienced some respiratory compromise. To evaluate both whether smoking cessation intervention would have this effect in a population of patients followed up longitudinally and to determine if the bronchodilator ipratropium could alter rate of loss of lung function, the Lung Health Study was initiated. This study comprised nearly 6,000 patients, one third of whom were treated with usual care and two thirds of whom received an intensive smoking cessation intervention. The smoking cessation intervention group was further divided into two groups, one of which received a placebo inhaler and one of which received an inhaler of ipratropium bromide (Fig 1, top left). This permits a number of observations. For example, to evaluate the effects of smoking cessation on loss of FEV^ those individuals treated with the placebo inhaler who quit smoking at the beginning of the study and remained abstinent (approximately 22% of the study group) can be compared with those individuals who smoked throughout the study despite all attempts at cessation (approximately 50% of the study group).
Figure 1. Lung Health Study (modified from Anthonisen et al). Top left: study design; top right: effect of smoking cessation. The analysis includes only those subjects in the intervention group treated with placebo. Continuous quitters are compared with continuous abstainers. Bottom left: effect of ipratropium based on comparison of the entire group treated with ipratropium vs the entire group treated with placebo. Bottom right: intention to treat analysis assessing benefits of smoking cessation intervention. Comparison is made between the usual care group and the smoking intervention placebo group.