Physiologic variants of chronic obstructive lung disease.

he term chronic obstructive lung disease T ( C O L D ) is used to designate a heterogeneous group of patients \\rho have persistent irreversible a iways obstruction of uncertain et ioloa. Until recently, these patients were thought to have an unpredictable course, an uncertain prognosis, and wry variable clinical manifestations. \Ye now know that most patients follo\w a slowly progressive course and have a longevit) which is closely related to the severity of their functional impairment. It has also become apparent that much of the variability in their clinical findings is related to the nature of their underlying disease. Patients with COLD can be divided into at least hvo clinical types. Before discussing these different patient types, a fern definition5 are necessary. "Chronic bronchitis" is defined symptomatically. I t denotes a chronic productive mugh of nonspecific etiology and is present in a large fraction of the total population. particularly in cigarette smokers. (There are morphologic changes in the bronchi which accompany bronchitic symptoms, but these are not the usual criteria for diagnosis. i Emphysema is defined anatomically as a dilatation of terminal air spaces in the lung \vith destruction of their n.alls. This anatomic change is forrnd in a great many "routine" poshortern examinations. even in patients who were not aware of respiratory difficulty during life. COLD, which is defined p l i ~ s i ~ l o g i c a l l ~ , is much less prevalent than