Chronic obstructive pulmonary disease

The Global Initiative for Obstructive Lung Disease defines chronic obstructive lung (pulmonary) disease (COPD) as “a common preventable and treatable disease, is characterized by persistent airflow limitation that is usually progressive and associated with an enhanced chronic inflammatory response in the airways and the lung to noxious particles or gases. Exacerbations and comorbidities contribute to the overall severity in individual patients.” The definition does not include the pathologic term emphysema and the clinical and epidemiologic term chronic bronchitis.

Patients with COPD frequently have a combination of obstructive bronchiolitis or small-airway disease and parenchymal destruction or emphysema (Figure 31-1). A ratio of forced expiratory volume in 1 sec (FEV₁) to functional vital capacity (FVC) of less than 0.7 is essential to make the diagnosis of COPD. Total lung capacity, residual volume, and functional residual capacity are all increased in COPD, which is different from the pattern seen with restrictive lung disease.

Clinical features

The Global Initiative for Obstructive Lung Disease has calculated the prevalence of COPD to be 6.1% and 13.5%, respectively, after 9-year and 10-year cumulative studies. In young adults, the prevalence was found to be 2.2%, and in patients 40 to 44 years of age, it was 4.4%. The primary cause of COPD is cigarette smoking (with α₁-antitrypsin deficiency as another cause in the young). Approximately half of patients older than 60 years of age who have a smoking history of at least 20 pack-years have a spirometry result consistent with COPD. Lung parenchymal destruction leads to loss of diffusing capacity and loss of the radial traction force on the airways. Airway inflammation produces increased mucus secretions and mucosal thickening, resulting in ventilation-perfusion mismatch and, finally, hypoxemia and CO₂ retention. Airway collapse on expiration results in air trapping, leading to dynamic hyperinflation because of auto-positive end-expiratory pressure (Figure 31-2).

Signs and symptoms of COPD vary from asymptomatic to overt disease, depending on the severity of the disease (Table 31-1). Extrapulmonary symptoms include diaphragmatic dysfunction, right-sided heart failure, anxiety, depression, and weight loss with evidence of malnutrition.

Table 31-1

GOLD Classification of COPD Severity

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Severity	Spirometry Results
	FEV1/FVC	FEV1 % of predicted value
Mild	< 0.7	≥ 80
Moderate