Study objectives: The guidelines of the National Lung Health Education Program for COPD screening proposed a shorter FVC maneuver (forced expiratory volume at 6 s of exhalation [FEV6]). Although reference values for FEV6 are available from the third National Health and Nutrition Examination Survey, forced expiratory flow between 25% and 75% of FVC (FEF25–75%) reference values for the shorter 6-s maneuver are not available and are needed. In particular, calculation of largest observed volume during the first 6 s of an FVC maneuver (FVC6), from a shortened FVC maneuver, is necessary because the FEF25–75% measurement is based on a percentage of FVC or, for a shorter maneuver, FVC6.
Design: We reanalyzed the raw volume-time curves from the third National Health and Nutrition Examination Survey to calculate FVC6, forced expiratory volume at 0.5 s of exhalation, forced expiratory volume at 3 s of exhalation, ratio of the FEV1 to largest observed volume during the first 6 s of an FVC maneuver expressed as a percentage (FEV1/FEV6%), and forced expiratory flow between 25% and 75% of the largest observed volume during the first 6 s of an FVC maneuver (FEF25–75%6) in addition to the previously reported values for FEV1, FEV6, and FEV1/FEV6%.
Patients or participants: Using the same normal, asymptomatic, nonsmoking reference population from a previous study, reference values for these parameters were derived from best values.
Results: A total of 2,261 white, 2,564 African-American, and 2,666 Mexican-American subjects aged 8 to 80 years were included in the analysis. Fifty-four subjects from the previous study were not included due to missing raw volume-time curves.
Conclusions: These reference values, utilizing the FVC6, provide investigators with the means of evaluating the relative merits of using the shorter FVC maneuver as a surrogate for the traditional FVC. They are needed particularly for calculating FEF25–75%, as statistically significant differences were observed between the FEF25–75% and FEF25–75%6.