Discriminating Measures and Normal Values for Expiratory Obstruction: Physiologic Defects in Current Smokers
Figure 2 shows marked differences in the variability of FEV1/FVC, FEV3/FVC, and FEF25-75 in never-smokers and current smokers for each fifth percentile of the respective populations when plotted against the percentage of the mean predicted values. The legend emphasizes misclassifications that would result if 80% of mean values was used as the threshold.
Figure 3 shows, for each gender of never-smokers and current smokers, the mean first spirometric fractions of forced expiratory maneuvers (ie, FEV1/ FVC) and last spirometric fractions (ie, 1 — FEV3/ FVC). Over this 60-year span for never-smokers, the average FEV1/FVC percentage decreases from 85.8 to 74.2%, while the average 1 — FEV3/FVC percentage increases from 2.2 to 12.6%. The absolute changes in FEV1/FVC and 1 — FEV3/FVC are nearly similar, whereas the relative changes are much larger for 1 — FEV3/FVC (Fig 3). There are minimal gender differences and even fewer ethnic differences. Thus, the proportion of flow occurring after the third second, while relatively small at age 20 years, increases markedly in association with older age.
The mean fraction of air expelled during the second and third second of forced expiration remains quite stable from ages 20 to 80 years (13 ± 4%). The fact that the correlations of FEV3/FVC with age are higher than those for FEV1/ FVC is noted in the legend of Figure 3. Importantly, current smokers have further significant decreases in FEV1/FVC and increases in 1 — FEV3/FVC (the SE for each point averages < 0.5%). By middle age, the fractions of FVC for current smokers are equivalent to those of never-smokers who are 20 years older. Table 3 shows the spirometric patterns (normal, expiratory obstruction, possible restriction, combinations, and uncertain) found in individual current smokers and indicates in what groups FEF25-75 values might be either confirmatory or suggest inappropriate interpretations. Fewer than 15 smokers (21 of 2,403 smokers) had exclusively abnormal and probably false-positive FEF25-75 (line a, Table 3). These 12 men and 9 women had average ages of 29 and 35 years, respectively. read only
Figure 2. The distribution of spirometric values as percentage of mean normal values. Top, A: FEV3/FVC. Middle, B: FEV1/FVC. Bottom, C: FEF25-75. Individuals are grouped by fifth percentiles above, at, and below mean normal values (using gender, age, height, and ethnicity) of 5,938 individual adult never-smokers from NHANES III data. Values for 3,570 adult current smokers are similarly grouped. In each graph, symbols extend laterally until the incidence is zero. The breadth of the distributions differs markedly, with least for FEV3/FVC and the most for FEF25-75. Vertical dashed lines separate those < 80% of predicted and > 80% of predicted means, and demonstrate the irrationality of using < 80% of predicted spirometric parameters to identify abnormal values. Using the 80% criterion, 0.0% of never-smokers and 1.5% of current smokers would have abnormal FEV3/FVC values; 0.6% of never-smokers and 7.9% of current smokers would have abnormal FEV1/FVC values; and 25.3% of never-smokers and 46.1% of current smokers would have abnormal FEF25-75 values.
Figure 3. Association of spirometric fractions with age and smoking. The values depicted were derived from NHANES III data for FEV1/FVC (top left and top right) and 1 — FEV3/FVC (bottom left and bottom right), for men (top left and bottom left) and women (top right and bottom right) from ages 20 to 80 years, and for 5,938 never-smokers and 3,570 current smokers. For never-smokers, the absolute changes in FEV1/FVC and 1 — FEV3/FVC are approximately equivalent but in opposite directions. FEV3/FVC correlations with age (never-smokers: men, r2 = 0.449; women, r2 = 0.437) are much higher than those of FEV/FVC (never-smokers: men, r2 = 0.220; women, r2 = 0.290). Relatively, 1 — FEV3/FVC changes more than FEV1/FVC with aging and cigarette smoking. The average SEM for current smokers is < 0.5%. By middle age, the spirometric values for average current smokers are similar to those of never-smokers who are approximately 20 years older.
Table 3—Spirometric Patterns for Normal, Expiratory Obstruction, Possible Restriction, or Combinations in 3,570 Current Smokers
Line and Spirometric Pattern | Test Result | No. | |||||
FVC | FEV1/FVC | FEV1/ FVC | FEV3/FVC | Total | ^^5-75 | ||
N | A | ||||||
(a) Normal | N | N | N | N | 2403 | 2382 | 21TI |
(b) Possible restriction | A | A | N | N | 167 | 105 | 62 |
(c) Possible restriction | A | N | N | N | 156 | 155 | 1 |
(d) Expiratory obstruction | N | N | A | A | 268 | 114 | 154 |
(e) Expiratory obstruction | N | A | A | A | 170 | 10§ | 160 |
(f) Obstruction ± possible restriction | A | A | A | A | 92 | 4§ | 88 |
(g) Late expiratory obstruction | N | N | N | A | 107 | 90 | 17 |
(h) Late expiratory obstruction | N | A | N | A | 12 | 2§ | 10 |
(i) Late expiratory obstruction ± possible restriction | A | A | N | A | 11 | 2 | 9 |
(j) Early expiratory obstruction | N | N | A | N | 104 | 67 | 37 |
(k) Early expiratory obstruction | N | A | A | N | 22 | 4§ | 18 |
(l) Early expiratory obstruction ± possible restriction | A | A | A | N | 15 | 1 | 14 |
(m) Uncertain | N | A | N | N | 39 | 21 | 18 |
(n) All other | 4 | 2 | 2 | ||||
(o) Total | 3,570 | 2,959 | 611 |