Chronic inflammation causes
structural changes and narrowing of the small airways.
Destruction of the lung parenchyma, also by inflammatory
processes, leads to the loss of alveolar attachments to the
small airways and decreases lung elastic recoil; in turn,
these changes diminish the ability of the airways to remain
open during expiration. Airflow limitation is best measured
by spirometry, as this is the most widely available,
reproducible test of lung function.