A PFT is a special computer designed test to measure the force of air exhaled and inhaled into the lungs. There are three measurements that are especially important when measuring lung functions. The Forced Vital Capacity (FVC) measures the total amount of air, in liters, in the lungs. The Forced Expiratory Volume (FEV1) measures the amount of air expelled in the first second the air is forced out of your lungs, this is usually restricted in asthmatics. The last measurement, and perhaps the most important in detecting asthma, is the Forced Expiratory Flow (FEF 25-75). This assesses the amount of air in the small airways, or bronchioles, which are usually narrowed in asthma.