Definitions of conditions associated with airflow obstruction

Chronic obstructive pulmonary disease (COPD)—Airflow obstruction that is usually progressive, not reversible, and does not change markedly over several months. It is predominantly caused by smoking
Chronic bronchitis—Presence of chronic productive cough on most days for 3 months, in each of 2 consecutive years, and other causes of productive cough have been excluded
Emphysema—Abnormal, permanent enlargement of the distal airspaces, distal to the terminal bronchioles, accompanied by destruction of their walls and without obvious fibrosis
Asthma—Widespread narrowing of the bronchial airways which changes its severity over short periods either spontaneously or after treatment