Chronic bronchitis is associated with?

• Chronic bronchitis is defined as a persistent cough with sputum production for at least 3 months in at least 2 consecutive years, in the absence of any other identifiable cause. It is strongly associated with smoking. • The earliest feature of chronic bronchitis is hypersecretion of mucus in the larger airways, associated with hypertrophy of submucosal gland of trachea and bronchi. • Although the numbers of glands increase slightly, the major increase is in the size of mucous glands. This increase can be assessed by Reid index which is the ratio of between the thickness of the submucosal glands to that of the bronchial wall. The Reid index (normal 0.4) is increased in chronic bronchitis. • Later, small airways (small bronchi and bronchioles) are also involved and show goblet cell hyperplasia and intraluminal and peribronchial fibrosis. • In most severe cases, there may be the obliteration of lumen due to fibrosis —» Bronchiolitis obliterans. • The bronchial epithelium may undergo squamous metaplasia and dysplasia.