Definition

The Global Initiative for Chronic Obstructive Lung Disease (GOLD) has published a working definition of chronic obstructive pulmonary disease (COPD):1 

"COPD is a common, preventable and treatable disease that is characterized by persistent respiratory symptoms and airflow limitation that is due to airway and/or alveolar abnormalities usually caused by significant exposure to noxious particles or gases”

 

Figure 1 illustrates how the chronic airflow limitation characteristic of COPD is caused by a mixture of small airway disease (obstructive bronchiolitis) and parenchymal destruction (emphysema).1 The relative contributions of these conditions to airflow limitation in COPD vary from person to person.1

Airflow limitation in COPD is caused by a combination of small airway disease and lung parenchymal destruction.

Figure 1. Airflow limitation in COPD is caused by a combination of small airway disease and lung parenchymal destruction.1

Obstructive bronchiolitis is due to chronic inflammation of the small airways (bronchiolitis). This inflammation results in scarring and remodelling of the small airways, that thickening the walls and leading to widespread narrowing.2  

Emphysema is characterised by the destruction of gas-exchanging airspaces (i.e. respiratory bronchioles, alveolar ducts and alveoli). Such destruction of parenchymal tissue is irreversible, and leads to limitation of expiratory airflow, small airway collapse and air trapping.3 

Hyperinflation is when a greater amount of air remains in the lungs following expiration. In patients with COPD, parenchymal tissue destruction also reduces the elastic recoil of the lungs and consequently the driving pressure that forces air out of the lungs.4 As a result, a large amount of energy is needed to exhale, which contributes to fatigue.5