ABSTRACT
Chronic bronchitis is defined as the presence of a cough productive of sputum (phlegm) on most days for three successive months in two consecutive years. It should be differentiated from emphysema, which is a pathological condition involving dilation of the terminal air spaces and destruction of alveolar walls. This turns the lungs from what is, in health, a very fine sponge into a very coarse sponge with loss of surface area over which gas exchange and absorption of oxygen (into the bloodstream) can occur. Both conditions may co-exist to a greater or lesser extent, with one or other predominating.
