In the past much importance has been placed on the distinction between chronic bronchitis and emphysema. In the majority of patients both conditions co-exist, usually in heavy cigarette smokers. Aetiology and prevalence Chronic bronchitis and emphysema are responsible for the personal disability and misery of tens of thousands of patients and impose a huge social and economic burden on society. Respiratory disorders are an important cause of death and of these chronic bronchitis and emphysema constitute a large proportion. Atmospheric pollution and occupational dust exposure are minor aetiological factors in chronic bronchitis and the dominant causal agent is cigarette smoke.
Smoking also causes emphysema, probably damaging the lung by the release of proteolytic enzymes.
In chronic bronchitis and emphysema the fundamental cause of reduced ventilatory capacity and breathlessness is the limitation of expiratory airflow. In emphysema a more important mechanism is the narrowing and collapse of airways during expiration as a consequence of loss of the lung elastic recoil which normally keeps airways open. Chronic bronchitis and emphysema develop over many years and patients are rarely symptomatic before middle age. Symptoms are initially minor, perhaps a morning cough productive of a little sputum. Initially breathlessness is on exertion but exercise capacity progressively and slowly deteriorates and eventually patients become respiratory cripples distressed by dyspnoea even at rest.