Chronic bronchitis

Chronic bronchitis is defined by the Medical Research Council as:
‘The production of sputum on most days for at least three months in at least two consecutive years.’

This definition describes a set of symptoms that are extremely common, if not universal, among long-term smokers and widely recognised as the ‘smoker’s cough’. Not all smokers whose illness fits the definition of chronic bronchitis will have an accelerated decline in lung function; 80% of smokers do not, after all, develop
COPD. However, the GOLD guidelines suggest that those with a persistent cough and sputum production and a history of exposure to risk factors should be considered ‘at risk’ and should be tested for airflow obstruction even if they do not complain of breathlessness. Recent research from the Netherlands has supported this suggestion.
Random testing of smokers aged between 35 and 70 years revealed a reduced FEV1 in 18% of all smokers. The percentage with a reduced FEV1 rose to 27% in smokers with cough and to 48% of smokers over 60 years who also had a cough.

Mucus in the airways is produced by mucus glands, situated mainly in the larger airways, and by goblet cells, found mainly in the lining of the smaller airways. Mucus glands produce about 40 times more mucus than the goblet cells, and it may be that the excess mucus production in smokers not affected by progressive airflow
obstruction reflects changes in the large airways.This chronic hypersecretion of mucus with little airflow obstruction, in the absence of other reasons for chronic mucus production such as bronchiectasis,is known as ‘simple bronchitis’. However, in at-risk smokers who are developing chronic airflow obstruction, excess mucus production seems to accelerate the rate of decline of their lung function.

Chronic production of mucus is unpleasant and may predispose the sufferer to lower respiratory tract infection, but on its own is not thought to be universally associated with the development of airflow obstruction. Excess production of mucus ceases in the majority of smokers when they stop smoking, although an initial
short-term increase is a common experience in smokers when they quit.