CHROMC BROriCMITIS



Chronic bronchitis is defined as a persistent cough resulting in sputum production for more than three months in each year over the previous three years. Diagnosis requires exclusion of other conditions associated with cough and sputum production, such as bronchiectasis. As with em­physema, cigarette smoke is the major etiologic factor, although exposure to other pollutants such as dusts may play a role by causing chronic irri­tation. The airway obstruction seen in the setting of chronic bronchitis is due to associated emphy­sema, bronchospasm, and obstruction of the pe­ripheral airways.

The findings on physical examination, pul­monary function assessment, and x-ray depend on the degree of associated airway obstruction. They range from normal to the pattern observed in em­physema, with the exception that diffusing ca­pacity remains normal. Gas exchange is worse than in patients with predominant emphysema, with hypoxemia and eventual hypercapnia in­creasing as the degree of air flow obstruction worsens. The marked hypoxemia leads to hypoxic pulmonary vasoconstriction and is responsible for the presence of pulmonary hypertension and the subsequent right-sided heart failure (cor pul­monale) often found in these patients. It also may result in significant polycythemia.

Chronic bronchitis and emphysema are marked by intermittent exacerbations that may precipitate acute respiratory failure. The underlying causes of these exacerbations include acute pulmonary infection, development of heart failure, and poor patient compliance. Until recently, an episode of acute respiratory failure in these patients was as­sociated with a poor prognosis following dis­charge (only 30 per cent survived five years), but with modern management such an episode does not appear to alter overall prognosis.