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. Patients with predominant bronchitis are prone to periodic infections. Patients with substantial emphysema tend to be very breathless, ventilating sufficiently to maintain normal arterial carbon dioxide and near- normal oxygen tensions. The development of cor pulmonale is a late and terminal event in these 'pink puffers' . There is evidence that optimum therapy and careful follow-up patients with cor pulmonale can produce good results.