Figure 1.02. A Forced Ventilatory Capacity (FVC) recording on which the volumes expired at the end of 0.5, 1, 2 and 3 seconds are indicated (FEV0.5, FEV1.0, FEV2.0, FEV3.0).
Figure 1.02. A Forced Ventilatory Capacity (FVC) recording on which the volumes expired at the end of 0.5, 1, 2 and 3 seconds are indicated (FEV0.5, FEV1.0, FEV2.0, FEV3.0).
Forced Expiratory Volume is greatest after 1/2 second and progressively decreases as expiration continues. The percentage of air expired at the end of the 1st, 2nd, and 3rd seconds as a percentage of the FVC are 83%, 94%, and 97%.
Air flow falls off as the lungs are emptied because as the lungs collapse, the air tubes are squeezed shut, raising resistance to flow.