Lung Volumes & Spirometry Reference Calculator
Calculate predicted lung volumes and spirometry reference values based on your age, height, and sex. Understand what spirometry results mean.
Lung Volumes and Spirometry Guide
Key Spirometry Measurements
FVC (Forced Vital Capacity): total volume of air that can be forcibly exhaled after a maximal inhalation. FEV1 (Forced Expiratory Volume in 1 second): the volume exhaled in the first second of a forced exhalation. FEV1/FVC ratio: the percentage of the FVC exhaled in the first second — normally above 70-75%. TLC (Total Lung Capacity): total air in lungs at full inflation. RV (Residual Volume): air remaining after maximal exhalation (~1.2L). These measurements require a spirometer and follow a sta
Obstructive vs Restrictive Patterns
Obstructive pattern (asthma, COPD, bronchiectasis): FEV1/FVC < 70%. FVC may be normal or mildly reduced. FEV1 is significantly reduced. The airways are narrowed — air cannot flow out rapidly in the first second but can eventually escape. COPD is graded by FEV1 as % predicted: Mild (GOLD 1) ≥80%, Moderate (GOLD 2) 50-79%, Severe (GOLD 3) 30-49%, Very severe (GOLD 4) <30%. Restrictive pattern (pulmonary fibrosis, obesity, kyphoscoliosis): FVC significantly reduced, FEV1 reduced proportionally, FEV
Reference Values and Ethnicity
Predicted lung volumes are based on population reference values from the European Respiratory Society (ERS/GLI 2012 equations). Predicted values vary significantly with sex, age, and height. A person's measured FEV1 is expressed as % predicted — below 80% is considered below normal limit. Ethnicity: Black African/Caribbean individuals have lung volumes approximately 10-15% lower than White Europeans of the same height and age. South Asian individuals approximately 5-10% lower. Reference equation
Spirometry in Clinical Practice
Spirometry is the gold standard for diagnosing and monitoring obstructive lung disease (asthma, COPD). NICE guidelines: spirometry should be performed to confirm COPD diagnosis — clinical features alone are insufficient. Reversibility testing: FEV1 improvement ≥12% and ≥200mL after bronchodilator suggests asthma (reversible obstruction) rather than COPD (less reversible). Peak expiratory flow rate (PEFR): a simpler bedside test — useful for asthma monitoring but less accurate than full spirometr
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