Emphysema and COPD Pathophysiology

Definitions and Pathophysiology

The European Respiratory Society defines COPD as a broader disorder characterized by reduced maximum expiratory flow and slow forced emptying of the lungs that encompasses both emphysema and airway disease components 1
COPD is characterized by reduced maximum expiratory flow and slow forced emptying of the lungs that doesn't change markedly over several months, with airflow limitation that is slowly progressive and irreversible 2
Emphysema is defined anatomically as a permanent destructive enlargement of airspaces distal to the terminal bronchioles without obvious fibrosis 3
COPD's airflow limitation results from varying combinations of airway disease and emphysema, with the relative contribution of these processes being difficult to define in living patients 1

Two major patterns of emphysema are recognized with distinct functional consequences Panacinar emphysema: involves destruction of the entire acinus 3
- Centriacinar emphysema: respiratory bronchioles, alveolar ducts, and alveoli at the center of the acinus are destroyed, but surrounding alveoli remain intact 3
An additional form is paraseptal emphysema, which affects areas adjacent to connective tissue septa 3

COPD includes several components, including emphysema: the parenchymal destruction component 1
Chronic bronchitis: defined by chronic or recurrent increases in bronchial secretions causing expectoration present on most days for at least 3 months a year, for at least two successive years 1
Small airway disease: characterized by inflammation, increased wall muscle mass, fibrosis, obliteration and airway narrowing 3

Emphysema specifically involves destruction of lung parenchyma with loss of alveolar attachments to the airway perimeter 1
COPD's airway component consists of decreased luminal diameters due to increased wall thickening, increased intraluminal mucus, and changes in the lining fluid of small airways 1
In COPD, changes also occur in pulmonary circulation, the right heart, and respiratory muscles as the disease progresses 3

Emphysema results in loss of lung recoil, which may appear early in the development of panacinar emphysema 3
In mild to moderate airflow limitation, the decrease in maximum flow could be due to either loss of recoil (emphysema) or small airway abnormalities 3
Emphysema is considered the most important factor in airflow limitation in severe COPD, while changes in small airways play a greater role in mild to moderate COPD 3

For COPD with emphysema, smoking cessation is essential, as recommended by the European Respiratory Society 1

Failing to recognize that emphysema is a component of COPD, not a separate disease entity, as stated by the European Respiratory Society 1
Not appreciating that emphysema predominantly affects lung parenchyma while COPD also involves airway disease 3

Emphysema is defined as permanent destructive enlargement of airspaces distal to the terminal bronchioles without obvious fibrosis, resulting in loss of lung elastic recoil and destruction of alveolar attachments to airway walls, causing airways to collapse during expiration, according to the American Thoracic Society 4
Mucus gland thickness relates to sputum production but not to loss of respiratory function, as noted by the European Respiratory Society 5
Airway eosinophilia is associated with measurable bronchodilator response to β-agonists and relatively less emphysema for any degree of airflow limitation, as reported by the American Thoracic Society 4

Lower diffusing capacity (DLCO) due to alveolar destruction is a characteristic of emphysema-dominant patients, as indicated by the American Thoracic Society 4
Less prominent cough and sputum production are typical of emphysema-dominant patients, according to the American Thoracic Society 5
High-resolution CT (HRCT) with quantitative analysis is the gold standard for phenotyping, as stated by the European Respiratory Society 6
DLCO is helpful in distinguishing emphysema (reduced) from pure airway disease (relatively preserved), though its value in planning treatment is less clear, as noted by the American Thoracic Society 4, 5
Static lung volume measurement documents hyperinflation degree, as reported by the American Thoracic Society 5

The presence of airway eosinophilia predicts better bronchodilator response to β-agonists, as indicated by the American Thoracic Society 4
Inflammatory cells in airways provide rationale for anti-inflammatory treatment only in some cases, specifically those with airway eosinophilia or frequent exacerbations, as noted by the American Thoracic Society 4