How to Calculate FEV1 Spirometry
What is FEV1 Spirometry?
FEV1 (Forced Expiratory Volume in 1 second) is the volume of air expelled in the first second of a forced breath out. FEV1/FVC ratio (Tiffeneau index) < 0.70 is diagnostic of obstructive lung disease. FEV1 < 80% predicted indicates airflow limitation.
Step-by-Step Guide
- 1FEV1/FVC < 0.70 → obstruction (COPD, asthma)
- 2FEV1 ≥ 80% predicted = normal
- 3FEV1 70–79% = mild obstruction
- 4FEV1 50–69% = moderate · FEV1 < 50% = severe
Worked Examples
Input
FEV1=2.5L · FVC=3.2L · predicted FEV1=3.5L
Result
FEV1/FVC=0.78 → obstruction · 71% of predicted → moderate
Both ratio and % predicted needed for staging
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