Not all people who smoke,develop COPD; and not all patients with COPD are smokers or have smoked in the past. There seems to be a varying susceptibility to lung damage due to cigarette smoke within the general population. Only a proportion of smokers (maybe only 10-15%) show a rate of decline of lung function over the years that is fast enough to result in the severe impairment that is typical of patients who present with breathlessness due to COPD. Susceptible subjects have an accelerated rate of decline of lung function (50-90ml of FEV1/yr compared with 20-30ml of FEV1/yr after the age of 30 in non-smokers). Subjects with COPD who stop smoking slow down the progression of disease and may return to normal levels of FEV1 decline. Unfortunately, they do not improve after they stop smoking (fig 3). By the time subjects are symptomatic with breathlessness, they will have already have severe impairment of lung function, and stopping smoking at this stage may extend their life expectancy but may not improve their symptoms.
Any occupation in which the local environment is polluted with the aforementioned gases and particulates increases the risk of developing of COPD. In addition, there is evidence that cadmium and silica also increase the risk of COPD. This is especially true if the subject smokes. Occupations at risk include coal miners, construction workers who handle cement, metal workers, grain handlers, cotton workers and workers in paper mills. However, the effect of smoking far outweighs any influences from the work environment.
Once COPD is established, repeated infective exacerbations of airflow obstruction, either viral or bacterial, may speed up the decline in lung function.

Website URL: http://hometown.aol.com/Jibaro6543/ourplace.html