Discriminating Measures and Normal Values for Expiratory Obstruction: Results
A total of 1,167 (ie, the sum of values from lines b to n, Table 3) of 3,570 smokers had abnormal patterns. Eight hundred one smokers had expiratory obstruction; 66% of smokers (530 of 801 smokers) [lines d to f, Table 3] had both early and late expiratory obstruction with or without possible restriction; 16% of smokers (130 of 801 smokers) [lines g to i, Table 3] had late expiratory obstruction with or without possible restriction; and 18% of smokers (141 of 801 smokers) [lines j to l, Table 3] had early expiratory obstruction with or without possible restriction. www.canadian-familypharmacy.com
Many smokers with expiratory obstruction had probable false-negative FEF25-75 test results. A total of 683 smokers (lines d, e, g, h, j, and k, Table 3) had expiratory obstruction but without restriction, 42% of whom (287 of 683 smokers) had normal and probable false-negative FEF25-75 test results. These results included 40% of smokers (114 of 268 smokers) with both abnormal FEV1/FVC and FEV3/FVC values (line d, Table 3) and 84% of smokers (90 of 107 smokers) with abnormal FEV3/FVC values (line g), with both groups being older (mean ages, 59 and 54 years, respectively). But, 64% of smokers (67 of 104 smokers) [line j, Table 3] with abnormal FEV1/ FVC values with normal and probable false-negative FEF25-75 test results tended to be younger. Thus, measurements of FEF25-75 especially in older individuals, often disagree with other spirometric measurements with less inherent variability.
This study introduces the concept of the 1 — FEV3/FVC fraction and gives data confirming the utility of the FEV3/FVC ratio in assessing expiratory airway obstruction We took advantage of the NHANES III-verified spirometric and demographic data that were available from a large and diverse US population, and expand on the prior excellent analyses of Hankinson et al by adding normal reference values for FEV3/FVC in white, black, and Latin men and women, 20 to 80 years of age (Table 2). We confirm the use of polynomial formula for FVC and FEV1 by Hankinson et al, and offer our linear regressions for FEV1/FVC and FEV3/FVC values over a broad age and height range for each gender and ethnic group. Variability in group and individual values for FEV1/FVC, FEV3/FVC, and FEF25-75, and our findings in current smokers confirm our hypothesis that FEF25-75 poorly discriminates normal values and those for expiratory obstruction (Fig 1, 2, Table 3). In contrast, FEV3/FVC correlates even better with age than FEV1/FVC and is an excellent measure of late expiratory obstruction (Fig 3, Table 3).