Chart — Pulmonary Function Testing
Flow-Volume Loop Patterns
A flow-volume loop tells you a great deal at a glance, because each pattern distorts the shape in its own way. Read the expiratory limb first — scooped means obstruction, tall and narrow means restriction — then look for the plateaus that flag an upper-airway lesion.
Written by Apex Respiratory Editorial Team
Educational use only. This material supports respiratory therapy education and exam review. It is not medical advice and is not a substitute for clinical judgment, institutional protocols, or physician orders. Always follow facility policies and current provider orders, and verify calculations independently before clinical use.
The Patterns
| Pattern | Loop Appearance | Hallmark | Typical Cause |
|---|---|---|---|
| Normal | Sharp peak, straight or convex expiratory limb, rounded inspiratory limb | Full volume, brisk flow | Healthy lungs |
| Obstructive | Concave (“scooped” / coved) expiratory limb, reduced peak flow | Scooped-out, prolonged expiration | COPD, asthma, emphysema (steeple in severe disease) |
| Restrictive | Tall, narrow loop; the shape is preserved but the volume is small | Shrunken FVC, witch’s-hat | Pulmonary fibrosis / ILD, chest-wall, neuromuscular |
| Fixed upper-airway obstruction | Plateau on BOTH the inspiratory and expiratory limbs | Both limbs flattened | Tracheal stenosis, large goiter |
| Variable extrathoracic obstruction | Plateau on the INSPIRATORY limb | Inspiratory flattening | Vocal cord dysfunction or paralysis, extrathoracic mass |
| Variable intrathoracic obstruction | Plateau on the EXPIRATORY limb | Expiratory flattening | Intrathoracic tracheal tumor, tracheomalacia |
How to Use This Chart
- Read the expiratory limb first: scooped means obstruction; tall and narrow means restriction.
- A plateau means an upper-airway (large-airway) lesion, and which limb flattens localizes it — extrathoracic hits inspiration, intrathoracic hits expiration, and a fixed lesion hits both.
- Confirm the shape with a clean, reproducible effort before interpreting it.
Related Resources
Sources
- Kacmarek RM, Stoller JK, Heuer AJ. Egan's Fundamentals of Respiratory Care. 12th ed. Elsevier; 2021. Flow-volume loop chapters.
- Pellegrino R, Viegi G, Brusasco V, et al. Interpretative strategies for lung function tests. Eur Respir J. 2005;26(5):948-968.