• Home
• Understanding
• Diagnosis
• Management of CF
• Management of CF Lung Disease
• Resources
• Glossary
• References

Measuring Lung Function

Pulmonary Function Tests^37,38

Pulmonary function tests (PFTs) use a spirometer to evaluate how well the lungs work, measuring the rate at which air moves into and out of the lungs. PFTs are used to detect lung diseases, to distinguish between different lung diseases, or to monitor the progression of a particular lung disease, such as cystic fibrosis. Normal PFT values are expressed as a percentage of the predicted value based on the person’s age, gender, ethnicity, and height.

Normal PFT values are based on the age, height, ethnicity, and gender of the person being tested. Results are expressed as a percentage. A value is usually considered normal if it is greater than 80% of the predicted value for that person.

Minute Ventilation

• Minute ventilation measures the total amount of air breathed in 1 minute.
• Most adults take 12 breaths per minute, moving 500 mL of air with each breath for a minute ventilation of about 6 litres per minute.

FEV₁

• FEV₁ is an abbreviation for forced expiratory volume in 1 second.
• FEV₁ measures the volume of air exhaled in the first second after a deep inhalation.
• A value>80% of the predicted value for a healthy person is considered normal.

FVC

• FVC is an abbreviation for forced vital capacity.
• FVC measures the amount of air exhaled with force after inhaling as deeply as possible.
• On average, FVC is 3 to 6 litres.

FEV₁/ FVC ratio

• The FEV₁/FVC ratio is the forced expiratory volume in 1 second as a percent of the FVC.
• The ratio helps show if the lungs are normal or exhibit an obstructive or restrictive disease pattern.
• If the ratio is >80% of the predicted value for the person tested, it is considered normal.

FEF_25-75

• FEF_25-75 is the force expiratory flow at 25% to 85% of vital capacity.
• It is considered a more sensitive measure of small-airway narrowing than FEV₁
• Its wide range of normality can make it difficult to interpret

References:
37. Tortora GJ, Derrickson B. The Respiratory System. In: tortora GJ, Derrickson B, editors. Principles of Anatomy and Physiolgy. 11th ed. Hoboken: John Wiley & Sons, Inc.; 2006. p. 846-94.
38. Marieb EN. The Respiratory System. In: Marieb EN, editor. Human Anatomy and Physiology. 5th ed. San Francisco: Benjamin Cummings; 1999. p. 834-80.