Forced Expiratory Volume in Adults

The Forced Expiratory Volume in 1 second (FEV₁, the volume of air a person is able to forcefully blow out in a second) is considered the best indicator of lung function in patients with CF since it correlates tightly with life expectancy and quality of life. This measurement is typically expressed as the percent from the normal reference values. In this case a number above 100% will represent lung function above normal and a value below 100% will represent lung function below normal.

Thus, the higher the number the healthier the lungs and the more likely the patient will experience better quality of life and less complications.