Pathology of COPD and asthma

Asthma and chronic obstructive pulmonary disease (COPD) are two distinct obstructive lung diseases with distinctive clinical presentations. Classically, asthma is characterised by airflow limitation that is reversible spontaneously or after adequate therapy, whereas COPD is characterised by airflow limitation that is never fully reversible and is usually progressive, regardless of adequate therapy. However, in clinical practice, the difference between the two conditions is much more complex because, with age, both asthma and COPD may cause an excess decline of lung function, and thus the development of a significant degree of irreversible airflow limitation. Since flow is the result of a driving pressure that promotes flow (elastic recoil of the lung parenchyma) and of an opposing resistance that contrasts flow (obstruction of the airways), a reduction in flow can be due either to a reduced driving pressure or to an increased resistance. When pathological changes are localised in the lung parenchyma, they reduce the driving pressure; conversely when these alterations involve the conducting airways, they increase the resistance. The present chapter will focus therefore on the pathological changes present in both conducting airways and lung parenchyma in COPD and in asthma in an attempt to highlight the possible mechanisms contributing to airflow limitation in these two conditions