Chronic Obstructive Pulmonary Disease

Chapter 303 | Part 7: Disorders of the Respiratory System

KEY CLINICAL POINTS

• COPD is defined by persistent respiratory symptoms and airflow obstruction, including emphysema, chronic bronchitis, and small airway disease.
• Smoking is the leading risk factor, but genetic factors like α 1-antitrypsin deficiency and environmental exposures (e.g., biomass fuels, air pollution) also contribute.
• Spirometry (FEV1/FVC < 0.7) is the gold standard for diagnosis, with severity graded by GOLD and ATS/ERS criteria.

1. DEFINITION & OVERVIEW

Chronic obstructive pulmonary disease (COPD) is a disease state characterized by persistent respiratory symptoms and airflow obstruction. It includes emphysema (alveolar destruction), chronic bronchitis (chronic cough and sputum production), and small airway disease. The Global Initiative for Chronic Obstructive Lung Disease (GOLD) defines COPD as airflow obstruction not fully reversible, typically due to environmental exposures like smoking or biomass fuels.

Table 303-1: GOLD vs. ATS/ERS Criteria for Airflow Obstruction Severity

SEVERITY	SPIROMETRY (GOLD)	SPIROMETRY (ERS/ATS)
Mild	FEV/FVC < 0.7 and FEV ‡ 80% predicted	FEV/FVC < LLN and zFEV > –1.645
Moderate	FEV/FVC < 0.7 and FEV 50–79% predicted	FEV/FVC < LLN and zFEV –1.65 to –2.5
Severe	FEV/FVC < 0.7 and FEV 30–49% predicted	FEV/FVC < LLN and zFEV –2.51 to –4
Very Severe	FEV/FVC < 0.7 and FEV < 30% predicted	FEV/FVC < LLN and zFEV < –4.1

1.1 Pathophysiology

Airflow obstruction results from airway disease (large airways), emphysema (alveolar destruction), and small airway disease. Cigarette smoke induces inflammation, protease-antiprotease imbalance, oxidative stress, and structural damage. Genetic factors like α 1-antitrypsin deficiency and HHIP gene variants also play roles.

1.2 Classification

COPD is classified into emphysema (centrilobular, panlobular, paraseptal), chronic bronchitis, and small airway disease. The GOLD classification system uses spirometry and clinical features to guide treatment.

2. EPIDEMIOLOGY

COPD is the fourth leading cause of death globally, affecting >15 million in the U.S. and projected to reach 592 million by 2050. Risk factors include smoking (pack-years), vaping, cannabis use, and genetic predispositions like α 1-antitrypsin deficiency (1 in 3000 individuals).

2.1 Demographics

Prevalence is higher in males historically, but female rates have increased. Smoking cessation reduces risk, but even ex-smokers may develop COPD. Occupational exposures (e.g., coal dust) and air pollution also contribute.

2.2 Global Impact

Globally, 480 million individuals have COPD, with significant burden in low- and middle-income countries. Tuberculosis and HIV infection are associated with COPD in non-smokers.

3. ETIOLOGY & PATHOPHYSIOLOGY

COPD arises from a combination of genetic susceptibility and environmental exposures. Key mechanisms include protease-antiprotease imbalance (e.g., α 1-antitrypsin deficiency), oxidative stress, and chronic inflammation. Small airway disease and emphysema are central to pathogenesis.

3.1 Inflammatory Pathways

Cigarette smoke activates macrophages and neutrophils, releasing proteases (e.g., neutrophil elastase) and oxidants. This disrupts extracellular matrix, leading to alveolar destruction and airway remodeling.

3.2 Genetic Factors

Variants in HHIP, FAM13A, and IREB2 genes are associated with COPD susceptibility. α 1-antitrypsin deficiency (PiZ phenotype) increases risk, especially in smokers.

4. CLINICAL FEATURES

Symptoms include chronic cough, sputum production, and dyspnea. Physical signs may include hyperinflation, barrel chest, and clubbing. Complications include respiratory infections, pulmonary hypertension, and lung cancer.

4.1 Symptomatology

Exertional dyspnea, chronic cough, and sputum production are common. Exacerbations (acute worsening) are marked by increased sputum volume, purulent sputum, and worsening breathlessness.

4.2 Physical Findings

Hyperinflation, prolonged expiration, and use of accessory muscles of respiration are noted. Cyanosis, cachexia, and clubbing may occur in advanced stages.

5. DIFFERENTIAL DIAGNOSIS

Differential diagnoses include asthma, interstitial lung disease, heart failure, and bronchiectasis. Overlap between asthma and COPD (especially in smokers) is common, but COPD is distinguished by irreversible airflow obstruction.

5.1 Asthma vs. COPD

Asthma is characterized by reversible airflow obstruction, while COPD has irreversible obstruction. Both may share airway hyperresponsiveness, but COPD is more common in smokers.

5.2 Other Conditions

Interstitial lung disease, pulmonary fibrosis, and heart failure must be excluded. Bronchiectasis and tuberculosis may mimic COPD in non-smokers.

6. INVESTIGATIONS & DIAGNOSIS

Spirometry (FEV1/FVC < 0.7) is the primary diagnostic tool. Chest CT identifies emphysema, and α 1-antitrypsin levels assess genetic risk. Arterial blood gases evaluate hypoxemia and hypercapnia.

6.1 Spirometry

Post-bronchodilator FEV1/FVC < 0.7 confirms airflow obstruction. GOLD and ATS/ERS criteria define severity based on FEV1 percentages.

6.2 Imaging

Chest CT detects emphysema patterns (centrilobular, panlobular) and airway wall thickening. Hyperinflation and bullae are common findings.

7. MANAGEMENT & TREATMENT

Management includes smoking cessation, bronchodilators (LABA, LAMA), inhaled corticosteroids, oxygen therapy, and pulmonary rehabilitation. α 1-antitrypsin augmentation is used in severe deficiency.

7.1 Pharmacologic Therapy

Dual bronchodilators (LABA + LAMA) are first-line for moderate-to-severe COPD. ICS are added for eosinophil counts > 300/µL. Roflumilast and azithromycin reduce exacerbations in severe cases.

7.2 Non-Pharmacologic Interventions

Pulmonary rehabilitation improves exercise capacity and quality of life. Oxygen therapy is indicated for resting hypoxemia (SpO2 ≤ 88%). Lung volume reduction surgery and transplantation are reserved for severe cases.

8. PROGNOSIS & COMPLICATIONS

Mortality is linked to severe airflow obstruction, hypercapnia, and complications like pulmonary hypertension and lung cancer. Exacerbations are a major driver of disease progression.

8.1 Exacerbations

Exacerbations increase mortality and hospitalization risk. Viral infections (e.g., RSV) and bacterial pathogens are common triggers. Non-pharmacologic interventions (e.g., pulmonary rehab) reduce exacerbation frequency.

8.2 Long-Term Outcomes

Annual FEV1 decline is 50–100 mL in smokers. Early intervention slows progression, but COPD is irreversible. Mortality is highest in patients with severe hypercapnia and comorbidities.

9. SPECIAL CONSIDERATIONS

Management in pregnancy, pediatrics, and the elderly requires tailored approaches. Women are increasingly affected, and COPD in the elderly is associated with frailty and comorbidities.

9.1 Pregnancy

Smoking cessation is critical. Oxygen therapy may be needed for fetal well-being. Bronchodilators are generally safe, but corticosteroids are used cautiously.

9.2 Pediatrics

Childhood respiratory infections (e.g., pneumonia) may increase COPD risk. Asthma-COPD overlap is common in smokers with a history of asthma.

10. KEY POINTS & CLINICAL PEARLS

1. Spirometry (FEV1/FVC < 0.7) is essential for diagnosis. 2. Smoking cessation is the most effective intervention. 3. Dual bronchodilators (LABA + LAMA) are first-line for moderate-to-severe COPD. 4. Oxygen therapy is indicated for resting hypoxemia. 5. α 1-antitrypsin augmentation is used in severe deficiency.