Emphysema Definition
Emphysema is defined anatomically as a permanent destructive enlargement of airspaces distal to the terminal bronchioles, without obvious fibrosis, leading to decreased lung function and impaired gas exchange. 1
Types of Emphysema
Emphysema presents in several distinct patterns, each with different pathological features and clinical implications:
Centriacinar (Centrilobular) Emphysema:
- Affects respiratory bronchioles, alveolar ducts, and alveoli at the center of the acinus
- Surrounding alveoli remain intact
- Most commonly associated with cigarette smoking
- Characterized by more small airways disease and less loss of elastic recoil 2
Panacinar Emphysema:
- Involves destruction of the entire acinus
- Results in earlier loss of lung recoil
- Often associated with alpha-1 antitrypsin deficiency 1
Paraseptal Emphysema:
- Affects areas adjacent to connective tissue septa
- Associated with lung scarring
- Often presents with subpleural bullae adjacent to areas of fibrosis 2
Pathophysiological Mechanisms
The destruction of lung tissue in emphysema occurs through several mechanisms:
- Protease-Antiprotease Imbalance: Increased proteolytic activity leads to degradation of elastin in alveolar walls 3, 4
- Oxidative Stress: Free radicals from cigarette smoke and inflammatory cells damage lung tissue 3
- Cellular Mechanisms: Programmed cell death (apoptosis), impaired autophagy, and cellular senescence contribute to tissue destruction 5
- Impaired Repair: Failure of normal lung repair mechanisms prevents restoration of damaged tissue 3
Structural and Functional Consequences
Emphysema contributes to airflow limitation through multiple mechanisms:
- Loss of Elastic Recoil: Destruction of elastic fibers reduces the lung's ability to recoil during expiration 1
- Loss of Alveolar Attachments: Reduces the tethering forces that help keep airways open 1
- Airspace Enlargement: Reduces the surface area available for gas exchange 1
- Ventilation-Perfusion Mismatch: Creates areas with high ventilation-to-perfusion ratios, contributing to hypoxemia 1
Clinical Implications
The structural changes in emphysema lead to significant clinical consequences:
- Dyspnea: Progressive shortness of breath, especially with exertion
- Reduced Exercise Capacity: Due to impaired gas exchange and increased work of breathing
- Hyperinflation: Air trapping leads to increased functional residual capacity and flattened diaphragm 1
- Intrinsic PEEP: Dynamic hyperinflation creates positive end-expiratory pressure that must be overcome during inspiration, increasing work of breathing 1
Diagnosis
CT scanning is the gold standard for identifying emphysema and its subtypes, allowing visualization of enlarged airspaces and specific patterns of destruction 2, 6. Pulmonary function tests typically show:
- Reduced FEV1 and FEV1/FVC ratio
- Increased total lung capacity and residual volume
- Decreased diffusion capacity (DLCO)
Clinical Relevance
Understanding the specific type and extent of emphysema is crucial for:
- Predicting disease progression
- Assessing risk of complications
- Determining appropriate management strategies
- Evaluating prognosis 2
The recognition of emphysema as a distinct pathological entity within COPD is important, as emphysematous COPD may respond differently to treatments compared to non-emphysematous COPD 3.