Obstructive Vs Restrictive Lung Disease

Obstructive and restrictive lung diseases represent two fundamentally different mechanisms of pulmonary dysfunction distinguished by pulmonary function testing (PFT) patterns. Obstructive lung diseases — including COPD (chronic bronchitis and emphysema), asthma, and bronchiectasis — are characterized by increased airway resistance that limits expiratory airflow. In chronic bronchitis, chronic inflammation of the bronchial mucosa causes goblet cell hyperplasia, mucus hypersecretion, and submucosal gland hypertrophy, narrowing the airway lumen. In emphysema, proteolytic destruction of alveolar walls (primarily by neutrophil elastase and matrix metalloproteinases unopposed by alpha-1 antitrypsin) destroys the elastic recoil that normally tethers small airways open during expiration, leading to dynamic airway collapse, air trapping, and hyperinflation. The loss of alveolar surface area also reduces gas exchange capacity, reflected in decreased diffusing capacity (DLCO). In asthma, reversible bronchospasm, airway inflammation with eosinophilic infiltration, and mucus plugging cause episodic airflow obstruction; airway remodeling with subepithelial fibrosis can develop with chronic uncontrolled disease. The hallmark PFT finding in obstructive disease is a reduced FEV1/FVC ratio below 0.70, with increased residual volume (RV) and total lung capacity (TLC) from air trapping. Restrictive lung diseases...