Obstructive vs restrictive pulmonology
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Obstructive vs. Restrictive Pulmonary Disease
These are the two fundamental physiological categories of diffuse lung disease, distinguished primarily by their patterns on pulmonary function testing (PFT).
Core Definitions
| Obstructive | Restrictive | |
|---|---|---|
| Mechanism | Increased resistance to airflow - partial or complete obstruction at any airway level | Reduced expansion of lung parenchyma - the lungs are "stiff" or the chest wall/neuromuscular apparatus limits inflation |
| Problem | Air can't get out fast enough | The lungs can't get big enough |
Robbins & Kumar Basic Pathology: "Obstructive disease [is] characterized by an increase in resistance to airflow... restrictive disease [is] marked by reduced expansion of lung parenchyma and decreased total lung capacity."
Causes
Obstructive:
- COPD (emphysema + chronic bronchitis) - most common; ~80% attributable to smoking
- Asthma - airway narrowing (reversible)
- Bronchiectasis - chronic airway dilation and inflammation
- Bronchiolitis obliterans
Restrictive - two broad categories:
- Intrinsic (parenchymal) - acute or chronic interstitial lung disease
- ARDS (acute)
- Pulmonary fibrosis (IPF), sarcoidosis, pneumoconioses, hypersensitivity pneumonitis (chronic)
- Extrinsic (extraparenchymal) - normal lungs, but restricted expansion
- Neuromuscular disease (Guillain-Barre, ALS, myasthenia gravis)
- Chest wall deformity (kyphoscoliosis)
- Severe obesity
- Pleural disease (effusion, fibrosis)
Pulmonary Function Tests (PFTs)
This is the cornerstone of differentiation:
| Parameter | Obstructive | Restrictive |
|---|---|---|
| FVC | Normal or slightly ↓ | ↓↓↓ |
| FEV₁ | ↓↓↓ | ↓↓ (proportional) |
| FEV₁/FVC ratio | ↓↓↓ (<0.70) | Normal (>0.80) |
| FEF₂₅₋₇₅% | ↓↓↓ | Normal |
| TLC | Normal or ↑ (air trapping) | ↓↓↓ (confirmatory) |
| RV | ↑ (gas trapping) | ↓ (or elevated in extraparenchymal) |
| FRC | Normal or ↑ | ↓↓↓ |
| PEFR | ↓↓ | Normal or ↓ |
| DLCO | ↓ in emphysema (alveolar destruction); normal in pure asthma/bronchitis | ↓ in ILD (thickened membrane); normal/↓ in extraparenchymal |
Bailey and Love's Short Practice of Surgery: "A low ratio indicates obstruction... A normal ratio (FVC and FEV₁ reduced to the same extent) indicates a restrictive pathology."
Key rule: TLC is the gold standard confirmatory test for restriction. Spirometry alone showing a "restrictive pattern" is confirmed only when TLC is below the lower limit of normal. In ~50% of cases where spirometry suggests restriction, lung volumes turn out to be normal (pseudorestriction from air trapping) - Murray & Nadel's Textbook of Respiratory Medicine.
Lung Volume Diagram
K.J. Lee's Essential Otolaryngology: In restrictive disease, all compartments (TLC, VC, IC, RV, FRC) are uniformly reduced. In obstructive disease - especially emphysema - TLC, RV, and FRC are all increased due to hyperinflation and air trapping.
Flow-Volume Loop Patterns
| Pattern | Shape |
|---|---|
| Normal | Triangular - rapid peak flow, gradual linear descent |
| Obstructive | Concave (scooped-out) expiratory limb - low peak flow, progressive slowing; the entire loop is shifted right (increased RV) |
| Restrictive | Narrow, tall loop - reduced volumes on both axes but the shape is preserved (no scooping); peak flow may actually be elevated relative to FVC |
Pathophysiology of Each Obstruction Mechanism
Emphysema: Permanent enlargement of air spaces distal to terminal bronchioles. Loss of elastic recoil means the airways collapse during forced expiration. The FEV₁ falls not because of intrinsic airway narrowing but because the driving pressure (elastic recoil) is lost.
Asthma: Bronchospasm + mucosal edema + mucus plugging narrows the lumen. Key distinguishing feature: reversibility - FEV₁ improves ≥12% and ≥200 mL after bronchodilator. Spirometry example from Bailey & Love: FEV₁ pre-bronchodilator 1.4 L → post-bronchodilator 2.5 L, FEV₁/FVC 40% → 71%.
Chronic Bronchitis: Hypersecretion and luminal inflammation; defined clinically (productive cough ≥3 months/year for ≥2 years).
Restrictive (ILD): Thickened alveolar walls impair gas diffusion AND reduce compliance - lungs are stiff. DLCO is the most sensitive early marker for ILD.
Mixed Defect
When both FEV₁/FVC and TLC are below the lower limit of normal, a mixed obstructive-restrictive defect is present. The FEV₁ % predicted is used to grade overall severity in these cases. - Murray & Nadel's Textbook of Respiratory Medicine
Quick Clinical Summary
| Feature | Obstructive | Restrictive |
|---|---|---|
| Prototype diseases | COPD, asthma | IPF, sarcoidosis, kyphoscoliosis |
| Symptoms | Wheeze, prolonged expiration, barrel chest (in emphysema) | Dyspnoea on exertion, dry cough, fine crackles (ILD) |
| CXR/CT | Hyperinflation, flat diaphragms (emphysema); bronchial wall thickening (chronic bronchitis) | Reticular pattern, honeycombing (ILD); reduced lung volumes |
| Bronchodilator response | May improve (especially asthma) | No improvement |
| PFT key | FEV₁/FVC < 0.70 | TLC < LLN, FEV₁/FVC normal |
Sources: Robbins & Kumar Basic Pathology; Bailey and Love's Short Practice of Surgery, 28th ed.; Murray & Nadel's Textbook of Respiratory Medicine, 2-Vol.; Barash, Cullen, and Stoelting's Clinical Anesthesia, 9e; K.J. Lee's Essential Otolaryngology.
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