Spirometry Calculator
Calculate FEV1/FVC ratio and interpret pulmonary function test (PFT) results. Classify lung disease pattern: obstructive (FEV1/FVC < 0.70), restrictive (low TLC), or mixed. Essential for COPD and asthma diagnosis.
Formula & Reference
| Variable | Symbol | Formula | Units |
|---|---|---|---|
| Spirometry Calculator | — | FEV1/FVC < 0.70 = obstruction | percent |
Step-by-Step Examples
FEV1=1.8L, FVC=3.2L, predicted FEV1=3.2, predicted FVC=3.8.
- FEV1/FVC = 1.8/3.2 = 56.3% (<70% = obstructive)
- FEV1 % predicted = 1.8/3.2 = 56.3%
- GOLD Stage 2 (Moderate COPD)
- Post-bronchodilator needed for diagnosis
FEV1=2.2L, FVC=2.5L, predicted FVC=4.0.
- FEV1/FVC = 2.2/2.5 = 88% (normal or high)
- FVC % predicted = 2.5/4.0 = 62.5% (low)
- Pattern suggests restriction — measure TLC
- TLC < 80% predicted confirms restriction
FEV1=3.2, FVC=4.0 (predicted both similar).
- FEV1/FVC = 80% (normal)
- Both values near predicted
- No obstructive or restrictive pattern
Real-World Applications
Common Mistakes to Avoid
GOLD guidelines require post-bronchodilator FEV1/FVC < 0.70 for COPD diagnosis. Pre-bronchodilator values may show reversible obstruction (asthma).
Spirometry requires maximal effort. Poor effort gives falsely low FEV1 and FVC. Trained technician and criteria for acceptability are essential.
Low FVC alone is not restrictive — obstruction also reduces FVC (air trapping). Restrictive requires low TLC measured by plethysmography.