COPD: Overview of Definitions, Epidemiology, and Factors Influencing Its Development
Despite considerable effort, the semantics regarding COPD remain confusing. As a whole, COPD is characterized by a single physiologic feature: limitation of expiratory airflow. A number of diseases can lead to this physiologic abnormality. In general, COPD embraces emphysema, chronic bronchitis, and asthma. Other conditions that may lead to limitation of expiratory airflow, for example bronchiectasis due to cystic fibrosis, are usually specifically excluded from the definition. The major conditions that may be embraced under the rubric “COPD” may be present independently or together to variable degrees in an individual patient. These relationships have been summarized by Snider and colleagues as a nonproportional Venn diagram. One of the important features of this definitional model is that the various diseases that may be included as part of COPD may be present without airflow limitation. canadian family pharmacy online
An alternative way to classify the component diseases that comprise COPD is anatomic. In this regard, asthma affects primarily the conducting airways. Emphysema is a destructive process of the alveolar structures. Chronic bronchitis affects both the large and the small airways. In the large airways, hypertrophy and hyperplasia of glandular structures and goblet cell metaplasia are prominent. In the small airways, peribronchiolar fibrosis and airway narrowing can be a prominent feature. Clearly these processes may exist independently or they may be present concurrently in a given patient. Finally, any of these processes may result in chronic airflow limitation and, therefore, they may be associated with COPD. Alternatively, these processes may be present anatomically without sufficient impairment of pulmonary function to qualify for the definition: COPD.