Chronic bronchitis, or the presence
of cough and sputum production for at least 3 months in
each of two consecutive years, remains a clinically and
epidemiologically useful term. However, it is important
to recognize that chronic cough and sputum production
(chronic bronchitis) is an independent disease entity
that may precede or follow the development of airflow
limitation and may be associated with development and/
or acceleration of fixed airflow limitation. Chronic bronchitis
also exists in patients with normal spirometry.