Step by Step
1
Obstructive lung disease — airflow OUT is blocked
Airways are narrowed, making it hard to exhale fully. FEV1 (the volume exhaled in the first second) is markedly reduced, while FVC (total forced vital capacity) is relatively preserved — giving a reduced FEV1/FVC ratio (below 70%). TLC is typically increased, due to air trapping.
2
Examples of obstructive disease
Asthma (reversible bronchospasm, treated with bronchodilators), COPD/emphysema (irreversible alveolar destruction and loss of elastic recoil), chronic bronchitis (mucus hypersecretion, associated with the "Blue Bloater" presentation), and cystic fibrosis.
3
Restrictive lung disease — lungs can't expand fully
Both FVC and TLC are reduced (the lungs simply can't hold as much air), but the FEV1/FVC ratio remains normal or even increased, since airflow itself isn't obstructed — the problem is limited lung expansion, not narrowed airways.
4
Examples of restrictive disease
Pulmonary fibrosis (stiff, scarred lungs), sarcoidosis, obesity (external restriction on lung expansion), neuromuscular disease (inability to generate the force needed to expand the lungs), pleural effusion, and pneumothorax.
Applied Walkthrough
1
A patient with long-standing emphysema undergoes spirometry. Their FEV1 is dramatically reduced, but their FVC is only mildly reduced — giving a low FEV1/FVC ratio, the hallmark of obstructive disease.
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This patient also shows an increased total lung capacity, reflecting air trapping — since damaged, less elastic airways collapse prematurely during exhalation, leaving extra air behind in the lungs.
3
A different patient with pulmonary fibrosis undergoes the same test. Both their FVC and TLC are reduced (their stiff, scarred lungs simply can't expand normally), but their FEV1/FVC ratio remains normal — since their airways themselves aren't obstructed, only their overall lung capacity is limited.
4
This contrast — reduced FEV1/FVC ratio in the emphysema patient versus a preserved ratio in the fibrosis patient, despite both having abnormal spirometry results — is exactly how these two disease categories are distinguished.
Exam Application
Exams test whether you can distinguish obstructive from restrictive lung disease based on spirometry findings (FEV1/FVC ratio and TLC), and whether you can correctly classify specific diseases (asthma, COPD, pulmonary fibrosis, etc.) into the correct category.
⚠ Common Trap
The most common trap is assuming both disease categories reduce lung capacity equally — obstructive disease often increases TLC (due to air trapping), while restrictive disease always decreases TLC (due to limited expansion) — these are opposite patterns, not the same direction of change.
✓ Quick Self-Check
1. What is the hallmark spirometry finding in obstructive lung disease?
A reduced FEV1/FVC ratio (below 70%), with FEV1 more affected than FVC.
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2. What is the hallmark spirometry finding in restrictive lung disease?
Reduced FVC and TLC, but a normal or increased FEV1/FVC ratio.
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3. Name two examples of obstructive lung disease.
Any two of: asthma, COPD/emphysema, chronic bronchitis, cystic fibrosis.
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4. Name two examples of restrictive lung disease.
Any two of: pulmonary fibrosis, sarcoidosis, obesity, neuromuscular disease, pleural effusion, pneumothorax.
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5. Why is total lung capacity often increased in obstructive disease but decreased in restrictive disease?
Obstructive disease causes air trapping (increasing TLC) due to airway collapse during exhalation; restrictive disease limits overall lung expansion (decreasing TLC).
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