How useful is the FEV1%?

The ability of the forced expiratory volume for 1 second expressed as a percentage of the forced vital capacity (FEV1%) in identifying early airway narrowing was compared with that of the forced expiratory flow in the middle half of the forced vital capacity (FEF 25-75%), in two populations, young smokers and subjects with allergic rhinitis who are known to have early airway narrowing. FEV1% appears to be more sensitive, in differentiating these groups and in identifying abnormality. Among smokers, FEV1% detected abnormality in 19% while FEF 25-75% only in 7% and among the allergic subjects the former detected abnormality in 25% while the latter only in 19%. In longitudinal studies, the decline in pulmonary function in smokers is identified almost equally well by both parameters. Critical ratios (t) were 2.85 and 3.86 after 1 to 2 years and 7.32 and 3.97 after 3 to 4 years for FEV1% and FEF 25-75% respectively. A high degree of correlation exists between these two measurements in all the subjects. These findings indicate the usefulness of FEV1% in the detection of early airway narrowing and are of special interest to those engaged in a busy clinical practice, as the FEV1% is a quicker measurement to make, than the FEF 25-75%.