Emphysema & Alveolar Destruction: Pathophysiology & Consequences

Emphysema: Structural Dismantling of the Gas-Exchange Surface

Emphysema is a COPD phenotype defined by permanent enlargement of airspaces distal to terminal bronchioles with destruction of alveolar walls—without significant fibrosis.

Pathologic Sequence

1. Protease-antiprotease imbalance: Smoke/pollutants → ↑ neutrophils/macrophages → release elastase, matrix metalloproteinases (MMPs). α₁-antitrypsin (A1AT) overwhelmed (genetic deficiency accelerates this).
2. Oxidative stress inactivates A1AT, damages matrix directly.
3. Alveolar wall destruction → loss of elastic recoil.
4. Coalescence into bullae (airspaces >1 cm) → ↓ surface area for gas exchange.
5. Airway collapse on expiration (loss of radial traction) → dynamic hyperinflation, air trapping.

Physiologic Consequences

• ↓ Diffusion capacity (DLCO) – hallmark.
• V/Q mismatch → hypoxemia, later hypercapnia.
• Work of breathing ↑↑ (hyperinflation flattens diaphragm → mechanical disadvantage).
• Pulmonary hypertension → cor pulmonale.
• Weight loss, cachexia (systemic inflammation, increased REE).

Clinical Presentation

• Progressive dyspnea (initially exertional, then at rest)
• Pursed-lip breathing, barrel chest, use of accessory muscles
• Quiet chest, hyperresonance, reduced breath sounds
• Chronic cough ± scant sputum (vs. chronic bronchitis)

Diagnosis

• Spirometry: FEV₁/FVC <0.70, FEV₁ ↓, poor bronchodilator response.
• CT: Centrilobular (upper lobe) or panlobular (lower lobe, A1AT) emphysema.
• DLCO markedly reduced.

Management

• Smoking cessation – only intervention slowing progression.
• Bronchodilators (LAMA/LABA), pulmonary rehab, vaccination.
• Supplemental O₂ if resting SpO₂ ≤88%.
• Lung volume reduction surgery (LVRS) / endobronchial valves for select upper-lobe predominant.
• Transplant for end-stage.
• A1AT augmentation if deficient.

Emphysema is irreversible; prevention and early intervention are paramount.