32. CHRONIC OBSTRUCTIVE AIRWAY DISEASE

Introduction

Chronic Obstructive Airway Disease (COPD) is a long-term, progressive lung disease where airflow becomes limited and is not fully reversible. According to GOLD (Global Initiative for Chronic Obstructive Lung Disease), COPD is defined as a disease state with airflow limitation that is usually progressive and caused by an abnormal inflammatory response of the lungs to harmful particles or gases.

The American Thoracic Society describes COPD as chronic airflow limitation mainly due to chronic bronchitis and emphysema. Many patients have features of both conditions, and COPD may also coexist with asthma.

Major Forms of COPD

1. Chronic Bronchitis

Defined as a productive cough (more than 30 mL sputum per day) for at least 3 months in a year for 2 consecutive years, excluding other causes of chronic cough.

It involves excessive mucus production, airway inflammation and swelling, leading to obstruction.

2. Emphysema

Characterized by permanent enlargement of air spaces beyond the terminal bronchioles and destruction of alveolar walls. This reduces the surface area for gas exchange and causes airway collapse during breathing out.

Epidemiology

  • Over 17 million Americans are affected.
  • Third leading cause of death in the USA.
  • More common in older men, but increasing in women due to rising smoking rates.
  • Asthma commonly coexists with COPD.

Etiology (Causes)

1. Cigarette Smoking (Most Common Cause)

  • Present in nearly 90% of COPD cases.
  • Smoking causes airway hyperreactivity, chronic inflammation and irreversible obstruction.

2. Alpha-1 Antitrypsin (AAT) Deficiency

  • A genetic disorder leading to early-onset emphysema.
  • AAT normally inhibits neutrophil elastase (a tissue-destroying enzyme).
  • Low AAT levels allow elastase to damage lung tissue.

3. Exposure to Irritants

  • Air pollution (sulfur dioxide), fumes, toxic gases.
  • Organic and inorganic dust exposure.
  • Smoke from biomass fuel (common in rural India).

4. Repeated Respiratory Infections

Infections weaken airway defenses and increase mucus accumulation.

5. Genetic, Social and Economic Factors

Pathophysiology

Chronic Bronchitis

  • Inflammation causes vasodilation, congestion and mucosal swelling.
  • Goblet cell hypertrophy → excessive mucus production.
  • More smooth muscle and reduced cartilage support.
  • Impaired cilia → poor mucus clearance.
  • Thick mucus blocks airways → productive cough.
  • Airways become infected with organisms like S. pneumoniae, H. influenzae, M. catarrhalis.
  • V/Q imbalance leads to hypoxemia (low oxygen) and hypercapnia (high CO2).
  • Chronic CO2 retention reduces sensitivity of brain respiratory centers.

Emphysema

  • Loss of lung elasticity due to destruction of alveolar walls.
  • Air trapping in alveoli → hyperinflation.
  • Breakdown of lung tissue and capillary beds.
  • V/Q imbalance improves by increased breathing rate; CO2 retention is less common than in chronic bronchitis.
  • Centrilobular emphysema: Common in smokers; affects respiratory bronchioles.
  • Panlobular emphysema: Seen in AAT deficiency; all lung segments affected.
  • Paraseptal emphysema: Affects lung periphery and associated with spontaneous pneumothorax.

Clinical Evaluation

Physical Findings

Chronic Bronchitis (“Blue Bloater”)

  • Onset usually after age 45.
  • Chronic productive cough, worse in the morning.
  • Progressive exertional breathlessness.
  • Obesity, wheezing, rhonchi.
  • Normal respiratory rate.
  • Right-sided heart failure in late stages (JVD, edema, hepatomegaly).
  • Cyanosis (bluish skin) may be seen.

Emphysema (“Pink Puffer”)

  • Onset usually after age 55.
  • Chronic cough with little sputum.
  • Severe breathlessness (dyspnea).
  • Weight loss, rapid breathing, pursed-lip breathing.
  • Barrel-shaped chest.
  • Hyperresonance on percussion.
  • Reduced breath sounds.

Most patients have mixed symptoms of both bronchitis and emphysema.

Diagnostic Test Results

General COPD Diagnosis

A patient is considered to have COPD if:

  • FEV1/FVC < 70% (post-bronchodilator)
  • FEV1 < 80% of predicted value

Chronic Bronchitis Findings

  • Blood test: Polycythemia due to chronic hypoxia.
  • High WBC count during infection.
  • Sputum: Thick, colored (yellow/green/white/gray).
  • ABG: Low PaO2 (45–60 mm Hg), high PaCO2 (50–60 mm Hg).
  • PFTs: Reduced FEV1/FVC, increased residual volume.
  • Chest X-ray: Hyperinflated lungs, increased bronchovascular markings.
  • ECG: Right ventricular hypertrophy.

Emphysema Findings

  • Sputum: Scanty, clear or mucoid.
  • ABG: Normal or slightly low PaO2 (65–75 mm Hg); late disease shows high PaCO2.
  • PFTs: Low FEV1/FVC, increased lung compliance, increased TLC and RV.
  • Chest X-ray: Bullae, blebs, flattened diaphragm, vertical heart, lung hyperinflation.

Detailed Notes:

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