PFT results have taken on greater importance as new therapies are tested and evaluated. One component of the PFT is the FEV1 value (the amount of air exhaled in one second). Physicians, families and patients keep track of the FEV1 values and decreases are investigated carefully and addressed with treatment modification, if necessary. Many industry-sponsored and CF Foundation-sponsored protocols use FEV1 values in their exclusion and inclusion criteria for studies involving patients with CF. FEV1 is used to judge the efficacy of most investigational treatments. (In many studies, change in FEV1 is the only primary endpoint measured.)