Definitions

COPD is an all-inclusive and nonspecific term that refers to a defined set of breathing-related symptoms: chronic cough, expectoration, varying degrees of exertional dyspnea, and a significant and progressive reduction in expiratory airflow. Most patients with COPD are smokers.1

Airflow obstruction does not show major reversibility in response to pharmacologic agents. Hyperinflation and a reduced diffusing capacity may be present. Inflammatory damage to both airways (bronchitis), and alveoli (emphysema), is found upon postmortem examination.

COPD is an umbrella term used to encompass several more specific respiratory conditions that may exist individually or in any combination. The terms chronic obstructive airways disease (COAD), chronic obstructive lung disease (COLD), chronic airflow (or airways) obstruction (CAO), and chronic airflow limitation (cal) all refer to the same disorder. The specific components of COPD are as follows:

Chronic Obstructive Bronchitis

Chronic obstructive bronchitis can be found in patients with cough, expectoration, and diminished airflow that does not improve significantly after bronchodilator inhalation. Simple chronic bronchitis, or chronic cough and expectoration with normal airflow, is not included in this definition. Simple chronic bronchitis without airflow obstruction has a good prognosis, and there is not such a severe social and economic impact on patients, their families, or society. (Chronic obstructive bronchitis is distinguished from asthmatic bronchitis, discussed below, only by its lack of reversibility in response to pharmacological agents.) Patients with pure chronic obstructive bronchitis do not have physiologic or roentgenographic evidence of hyperinflation. Diffusion tests are normal or nearly so.

Emphysema

Historically, emphysema was defined pathologically as reduced elastic recoil and the disintegration of alveolar walls due to tissue breakdown through the processes summarized in Section D. Clinically, emphysema patients exhibit varying degrees of dyspnea upon exertion and irreversible airflow obstruction. These patients also demonstrate abnormalities at the air/blood interface that manifest in decreased carbon monoxide uptake (measured by diffusion tests) and hyperinflation (judged clinically by physical examination, x-ray, and measurements of total lung capacity). Chronic bronchitis and emphysema, of course, usually coexist because both are caused by tobacco smoking. Most clinicians continue to use the term “COPD” for this reason.

Asthmatic Bronchitis

Patients with asthmatic bronchitis have pulmonary symptoms, including productive cough, exertional dyspnea, and airflow obstruction, but these symptoms and the obstruction reverse significantly in response to inhaled beta-agonists, anticholinergics, methyl-xanthines, and corticosteroids (used either alone or in combination). In these patients, progressive airflow obstruction occurs over time and becomes less reversible.

Diagnosing asthmatic bronchitis in its early stages, when airflow abnormalities are just beginning to occur, may be profoundly important. In both asthmatic and chronic bronchitis, bronchial hyperreactivity probably results from airways inflammation caused by a variety of irritants (including smoke). This hyperrespons-iveness is likely to reverse significantly if the patient stops smoking, avoids other irritants, and uses bronchodilators. The regular use of bronchodilators or inhaled corticosteroids in the early stages of disease may help forestall or prevent irreversible damage and may make impairment, disability, and death from “endstage” COPD less likely.

In their later stages, chronic obstructive bronchitis and asthmatic bronchitis may become indistinguishable. Therefore, airflow obstruction that is chronic, progressive, and partially reversible in response to bronchoactive drugs is the key indication of the bronchial component of COPD.

References

Petty TL, Hodgkin JE. Definitions and epidemiology of COPD. Chapter 1 in Hodgkin JE, Petty TL (eds). Chronic Obstructive Pulmonary Disease: Current Concepts. Philadelphia: WB Saunders, 1987. This chapter presents useful clinical definitions for COPD.

1 The definition of COPD has varied over the years. Today it includes ICD-9 codes for chronic bronchitis (491), emphasema (492), and other chronic airways obstruction (494-496). Isolated asthma, particularly reversible asthma (493), is not included.