INTRODUCTION AND EPIDEMIOLOGY
Chronic obstructive pulmonary disease (COPD) is a common, preventable, and treatable disease 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.1-6 COPD often presents with symptoms of dyspnea, chronic cough or sputum production, and/or a history of exposure to known risk factors for the disease such as cigarette smoke. The World Health Organization Global Initiative for Chronic Obstructive Lung Disease COPD definition encompasses chronic bronchitis, emphysema, bronchiectasis, and asthma, recognizing that most patients have a combination of the different diseases. COPD is the third leading cause of death in the United States, with women now accounting for >50% of COPD-related deaths.
CHRONIC COMPENSATED OBSTRUCTIVE PULMONARY DISEASE
Although tobacco smoke is the major risk factor for developing COPD, only 15% of smokers will develop COPD. Occupational dust, chemical exposure, and air pollution are other risk factors for developing COPD. α1-Antitrypsin deficiency accounts for <1% of COPD patients.
Irritants, notably tobacco smoke and air pollutants, trigger an increase in inflammatory cells in the airways, lung interstitium, and alveoli. Proteases break down lung parenchyma and stimulate mucus secretion. Mucus-secreting cells replace cells that normally secrete surfactant and protease inhibitors. These changes result in a loss of elastic recoil, narrowing, and collapse of the smaller airways. Mucous stasis and bacterial colonization then develop in the bronchi. The earliest objective changes in the evolution of COPD are often clinically imperceptible; these early changes are small increases in peripheral airway resistance or lung compliance. Because dyspnea and hypersecretion often progress insidiously, it may take decades before COPD becomes clinically evident. The Global Initiative for Chronic Obstructive Lung Disease guidelines are helpful for the early diagnosis and treatment of COPD (Table 70-1),6 although there is only a weak correlation between forced expiratory volume in 1 second (FEV1), symptoms, and health-related quality of life.6
TABLE 70-1Classification of COPD Severity2-6 |Favorite Table|Download (.pdf) TABLE 70-1 Classification of COPD Severity2-6
|Stage ||In Patients with FEV1/FVC <0.7: |
|Mild COPD ||FEV1 ≥80% predicted |
|Moderate COPD ||FEV1 between 50% and 79% predicted |
|Severe COPD ||FEV1 between 30% and 49% predicted |
|Very severe COPD ||FEV1 <30% predicted |
The central element of chronic lower airway obstruction is impedance to expiratory airflow due to increased resistance or decreased caliber of the small bronchi and bronchioles. Airflow obstruction results from a combination of airway secretions, mucosal edema, bronchospasm, and bronchoconstriction. Exaggerated airway resistance reduces total minute ventilation and increases respiratory work.
In emphysema, distortion or destruction of alveolar and capillary surfaces results in alveolar hypoventilation and ventilation–perfusion ...