Obstructive lung disease vs Restrictive lung disease
How to tell Obstructive lung disease and Restrictive lung disease apart when a board question makes them look alike.
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The first branch point is post-bronchodilator FEV1/FVC, because a ratio below 0.70 indicates obstruction.
Side by side
Post-bronchodilator FEV1/FVC below 0.70 identifies airflow obstruction.
Reduced total lung capacity below 80% predicted with preserved or high FEV1/FVC identifies restriction.
Airway narrowing or collapse increases expiratory resistance and causes air trapping.
Reduced lung or chest wall compliance limits maximal lung expansion and decreases total volumes.
Obstructive pattern: post-bronchodilator FEV1/FVC <0.70, elevated RV or RV/TLC ratio from air trapping, and reduced DLCO in emphysema but often normal in chronic bronchitis or asthma.
Restrictive pattern: TLC <80% predicted, often reduced FVC with normal or elevated FEV1/FVC, and DLCO low in interstitial lung disease but near normal in obesity or neuromuscular causes.
The trap
Low FVC is often mislabeled as restriction without lung volumes. The resolving clue is TLC measurement: true restriction requires low TLC, while severe obstruction can lower FVC from air trapping with high RV.
The repair move
Next best step: obtain complete pulmonary function testing with bronchodilator response, lung volumes, and DLCO before labeling the pattern. If obstruction is confirmed, initiate inhaled bronchodilator therapy and risk-factor modification such as smoking cessation. If restriction is confirmed, direct testing toward interstitial, neuromuscular, or chest wall causes and treat the underlying driver.
Try a free question
CoreA 58-year-old woman has chronic dyspnea. Post-bronchodilator spirometry shows FEV1/FVC 0.62 and FEV1 58% predicted. What is the most likely physiologic pattern?
Show answer and explanation
Answer: A. Obstructive lung disease. A post-bronchodilator FEV1/FVC below 0.70 defines obstructive ventilatory physiology.
Why the other choices are tempting
- B. Restriction requires low TLC, which is not provided and cannot be inferred from ratio below 0.70.
- C. These values are abnormal and not consistent with normal mechanics.
- D. A diffusion defect alone does not explain the reduced ratio.
- E. Upper airway obstruction has different flow-volume loop features rather than this classic obstructive ratio pattern.
Flashcards
Tap a card to flip it.
Which spirometric cutoff defines obstructive physiology after bronchodilator testing?
FEV1/FVC below 0.70 defines airflow obstruction.
What additional test confirms restrictive physiology when FVC is low?
Lung volume measurement showing TLC below 80% predicted confirms restriction.
Quick answers
What is the fastest way to tell Obstructive lung disease from Restrictive lung disease?
The first branch point is post-bronchodilator FEV1/FVC, because a ratio below 0.70 indicates obstruction.
What is the key clue for Obstructive lung disease?
Post-bronchodilator FEV1/FVC below 0.70 identifies airflow obstruction.
What is the key clue for Restrictive lung disease?
Reduced total lung capacity below 80% predicted with preserved or high FEV1/FVC identifies restriction.
What is the common trap with Obstructive lung disease vs Restrictive lung disease?
Low FVC is often mislabeled as restriction without lung volumes. The resolving clue is TLC measurement: true restriction requires low TLC, while severe obstruction can lower FVC from air trapping with high RV.