🌬️ Patterns of Lung Disease
- Respiratory disease is broadly classified into obstructive (airway narrowing) and restrictive (reduced lung expansion) patterns.
- While not every case fits neatly, this division guides diagnosis and management.
- DLCO (Diffusion Capacity Test): Measures oxygen transfer across the alveolar-capillary membrane — especially valuable in interstitial lung diseases.
- Remember: PFTs are effort-dependent, so poor technique may mimic disease. ⚠️
🗂️ Restrictive vs Obstructive: Quick Comparison
| Pattern | Examples | Spirometry Findings | DLCO |
|---|---|---|---|
| Obstructive | Asthma, COPD, Bronchiectasis | ↓ FEV1, ↓ FEV1/FVC ratio (<70%) | Usually normal, ↓ if emphysema |
| Restrictive | Interstitial lung disease, Obesity, Neuromuscular weakness | ↓ FVC, Normal or ↑ FEV1/FVC ratio | ↓ in parenchymal causes (e.g. pulmonary fibrosis) |
🩻 Imaging Studies
- Chest X-ray: First-line for infections, tumours, chronic lung changes.
- CT Scan: High-resolution CT is gold standard for ILD and bronchiectasis.
- MRI: Limited role; useful for mediastinal or chest wall tumours.
- Ultrasound: Best for pleural effusions, guides thoracentesis.
📊 Pulmonary Function Tests (PFTs)
- Spirometry: Measures FEV1, FVC, FEV1/FVC — cornerstone test for asthma/COPD.
- Peak Flow: Quick outpatient test; useful for asthma monitoring.
- Body Plethysmography: Measures total lung capacity (TLC); diagnostic for restrictive disease.
🧪 Laboratory Tests
- ABG: Identifies hypoxaemia/hypercapnia.
- Sputum culture/cytology: Infections, cancer cells.
- FBC: Anaemia or infection clues.
- Allergy testing: Triggers in asthma or hypersensitivity pneumonitis.
🔍 Endoscopic Procedures
- Bronchoscopy: Direct airway view, biopsies, BAL.
- Thoracoscopy: For pleural disease, minimally invasive.
- Mediastinoscopy: Lymph node sampling, e.g., staging lung cancer.
🧵 Biopsy Procedures
- Lung Biopsy: For cancer, ILD, infections.
- Pleural Biopsy: Diagnoses TB, malignancy.
- Needle Aspiration: CT/US guided, minimally invasive.
☢️ Nuclear Medicine
- V/Q Scan: Classically for PE diagnosis (especially if CTPA contraindicated).
- PET Scan: Evaluates cancer, inflammatory foci.
🏃 Cardiopulmonary Exercise Testing (CPET)
- Assesses integrated lung, heart, and muscle function. Useful in unexplained dyspnoea or pre-surgical risk stratification.
Exam Tip: 👉 Obstructive = ↓ FEV1/FVC. 👉 Restrictive = ↓ TLC, normal or ↑ ratio. 👉 Always interpret PFTs alongside imaging and clinical history.